Transactions
of THE
Illuminating Engineering
Society
VOL. X
JANUARY-DECEMBER
1915
Subject Index and Index to Authors
ILLUMINATING ENGINEERING SOCIETY
29 WEST THIRTY-NINTH STREET
NEW YORK
7p
100
J
SUBJECT INDEX.
* Pages following the numbers given should also be consulted in
referring to a topic or subject.
PAGE
Accidents and poor illumination 868
Animals :
Experiments on vision of 502
Arc lamps: (See also Lamps)
Photometry 1
Armory and gymnasium lighting 747
Data on various installations 1186
Art and science in home lighting 55
Artificial daylight units, some data on 219
Atmospheric pressure, effect on candlepower of various flames 843
Automobiles, headlights 920, 926, 928, 1017, 1022, 1035
Barometric pressures in various cities in the United States 863
Bibliography 222, 314, 561
Car lighting problems 245
Mercury-vapor lighting 902
Photometry 318
School lighting 199
Vision in animals 513
Books on illumination 222
Brightness :
Defined 374, 643
Measurements 773
Normal, defined 644
Specular 359
Calculation :
Illumination 555, 587, 593
Of daylight 615
Candlepower :
Effect of atmospheric pressure on various flames 843
Mean spherical, mean hemispherical, mean horizontal, mean
zonal, defined 646
Car lighting:
Street, a practical study of 227, 546
Central stations :
How can gas and electric companies under one management
render the best service ? 793
Code of lighting for factories, mills and other work places 605
IV TRANS. I. E. S. VOL. X
Color : PAGE
Edridge-Green theory of vision 578
Esthetic value of yellow light 1024
Preferences 1036
Vision 576, 577
Vision theories 259
Yellow light, its importance in lighting 1015
Color music and lighting 5°°
Colored light photometry: (See also Photometry)
Application of Crova's method of colored light photometry to
modern incandescent illuminants 716
Compensated test-plate for illumination photometers 727
Crova's method of colored light photometry 716
Daylight :
Artificial units, some data on 219
Calculations of 615
Requirements for factories, mills, etc 609
Definitions (see Nomenclature)
Diffusion 353
Efficiency (defined) 364
Integrating instruments and methods 368
Interior furnishings 397
Optical properties of diffusing media 353, 366
Optical properties of photographic papers 388
Papers and inks 379
Pure and partial 362
Selective instruments and methods 371
Specular 354, 361, 364
Theory of 360
Disease :
Light in the treatment of disease 137
Edridge-Green theory of color vision 578
Efficiency :
Diffusion 364
Eye 448
Luminous 559
Efficiency of the eye (see Eye)
Electric and gas lighting companies :
How can best light service be rendered under one manage-
ment 793
Eye:
After images 1004
A resume of the physical, physiological, and psychic phases
of vision 562
Colors of light preferred 1036
Color vision 576
SUBJECT INDEX V
Eye {continued) pace
Disorders of 1007
Effect of glare on vision 1000
Effect of motion pictures on efficiency 491
Efficiency under different conditions of lighting; effect of
varying distribution factors and intensity 407
Experiments on vision of animals 502
Fatigue, influence of lights of different color 1020
Further experiments on the efficiency of the eye under differ-
ent conditions of lighting 448
Light intensity 407
Purkinj e phenomenon 575
Retinal phenomena 1002
Safeguarding eyesight of school children 181
Some experiments on the eye with inverted reflectors of
different densities 1097
Tests for efficiency under different systems of illumination.. 408
Ultra-violet radiation, effect of 932
Vision and yellow glasses 1019
Vision: (See also heading Vision)
mechanical theory of 576
physical, physiological and psychic phases 562
Visual acuity 573
and monochromatic light 1017
Factory lighting (see Industrial lighting)
Fixtures :
Progress in manufacture 548
Flame arc lamps (see Lamps)
Flashlights 530
Flicker photometry (see Photometry)
Foundry lighting (see Industrial lighting)
Gas and electric lighting companies :
How can best light service be rendered under one manage-
ment ? 793
Gas lighting:
Atmospheric pressure effect on flames 843
Automatic clock lighting attachment 1083
Automatic lighters 518
Burners 517
Heating value 519
How can a company render best light service, 793
Lamps :
candlepower variations with barometric pressure 843
high pressure (see Street lighting)
pilot flame ignition 670
rating of 556, 647, 649
VI TRANS. I. E. S. VOL. X
Gas lighting {continued) PAGE
Panama-Pacific Exposition 1083
Pilot flame ignition 670
Piping for works 296
Streets (see Street lighting)
Variation in candlepower with atmospheric pressure of several
types of burners 852
Glare :
Brightness 397
Contrast 397
Definitions 992
Diffusing media, optical properties of 353, 366, 388
Effect on vision IOOO
From automobile headlights 1017
From illuminants 401
From typewriter papers 385
From walls and wall coverings 398
From writing papers 384
Furniture and fixtures 400
General report on, by I. E. S. committee 987
Interior furnishings 397
Legislation 557
Papers and inks 379
Photographic papers 388
Veiling 398, 1012
Window envelopes 394
Glassware :
Glass, manufacture of for lighting 1086
Recent developments 548
Gymnasium lighting 746
Headlights :
Automobile 920, 926, 928, 1022
Incandescent 271
Legislation 558
Locomotive 919
Parabolic mirror 914
Recent developments 528
Hering theory of color vision 577
Heterochromatic photometry (see Photometry)
High pressure gas lighting (see Street lighting)
Home lighting 55
Illuminating engineering:
As a branch of technical instruction 321
Definitions and terminology 642
SUBJECT INDEX Vll
Illumination: (See also Lighting) PA°E
A flux method of obtaining average illumination 593
And one year's accidents 868
Books on < 222
Calculations 555, 587, 593, 615
Daylight 2I9
Effect of good lighting on industrial production 617
Lighthouse 2°9
Measurements (see Photometry)
Principles and theory, books on 22"
Problems special, and small incandescent lamps 1171
Progress, report of committee 5X5
Small interiors 303
Use of portable photometers 766
Incandescent lamps (see Lamps)
Industrial lighting:
Accidents and illumination 868
Clothing factories 898
Code of °°5
Cotton mills 894
Daylight °°9
Effect of good lighting on production 617
Glass factories 899
Intensities required °°°
Machine shops 886
Maintenance °3°
Metal working plants 885
Motion picture studios 900
Newspaper and printing plants 896
Old and new lamps for 6l9
Paper mills 898
Power houses 898
Safety and illumination 619
Silk mills • S02
Skylights 614
calculation for 0I°
Systematic procedure for remodeling poor installations 630
Warehouses 9°°
Window glasses for daylighting 6l3
With mercury-vapor lamps 883
Wood working plants 892
Woolen mills ^
Integrating sphere: (See also Photometry)
Notes on the integrating sphere and arc lamp photometry... I
Interior lighting (see Lighting)
Lambert, defined 555, 644
Vlll TRANS. I. E. S. VOL. X
Lamps : PAGE
Arc :
photometry I
street lighting 4°5
use in photography 951
Arc (flame) 405
recent developments 525
use in photography 951. 959
Arc, magnetite 4°5
Characteristic, performance, horizontal distribution and ver-
tical distribution curves, defined 645
Efficiency of 647
Elliott kerosene :
variation in candlepower with barometric pressure... 856
Hefner :
variation of candlepower with barometric pressure... 844
Gas 671
Incandescent: (See also Lamps by name)
life testing of Bureau of Standards 814
Life tests of 647
Mercury-vapor :
for industrial lighting 883
use in photography 951
Miner's 528
Oil 520
Old and new for industrial lighting 619
Pentane :
variation of candlepower with barometric pressure . . . 844
Photographic and visual efficiencies of various illuminants . . . 963
Proj ection 527
Rating 5*4
Small incandescent and special illumination problems 11 71
Spherical reduction factor 646, 674
Tungsten:
application in photography 149
Tungsten, blue glass bulb :
use in photography 95*
Tungsten (gas-filled) :
physics 522
recent developments 520
Tungsten, vacuum :
recent developments 522
use in photography 951
Type C (see Tungsten, gas-filled)
Lamp-posts (see Street lighting)
SUBJECT INDEX IX
PAGE
Legislation 557
Glare 557
Lighting code °°5
Safety lighting 558
Light: (See also Photometry)
Artificial daylight 2I9
Cold, theory of 289
Colors preferred I03°
Esthetic value of yellow light 1024
Physics of :
books on 222
Projection, new developments 38
Uses in the treatment of disease *35
Yellow, a discussion of its importance in lighting 1015
Lighthouse illumination 2°9
Lighting: (See also Illumination and Industrial lighting)
Accidents and illumination 868
Armories 746, 1 186
Art and science in home lighting 55
Books on 222
Calculations (see Illumination)
Car 227> 546
Clock tower 547
Code for factories, mills and other work places 605
Color and music 500
Definitions and terminology °42
Diffusion :
interior furnishings 397
papers and inks 379
photographic papers 388
optical properties of 353. 366
Efficiency of the eye under different conditions of lighting,
and effect of varying the distribution factors and
intensity 407, 448
Eye:
efficiency under different conditions of lighting. . .407, 448
Factory, code of °°5
Fixtures, progress in manufacture of 548
Flood 543
Gas (see Gas lighting)
Glass, manufacture of I086
Gymnasium 740
Home:
art and science in 55
Hospitals 546
X TRANS. I. E. S. VOL,. X
Lighting {continued) page
Hotel 545
How can gas and electric companies under one management
render the best light service? 793
Industrial (see Industrial lighting)
Kerosene lamp, light of 1034
Knowns and unknowns in the lighting of small interiors.. .. 303
Legislation 557, 605
Lighthouse 209
Locker-room 751
Measurement of lighting (see Photometry)
Modern street car 82
Municipal buildings 546
Nomenclature and standards 642
Offices 546, 651, 659, 600
Panama-Pacific Exposition 534
Passenger boats and steamers 681
Photometry (see Photometry)
Railway cars 82, 227, 546
Residence (see Home lighting)
Rifle ranges 750
School 181
Semi-direct, office 691
Service of companies to customers 793
Small interiors 303
Street 281, 405, 537, 1039
Street car 82, 227, 546
Symbols 648
Tennis courts 544
War 530
Lighting code 605
Literature :
Bibliographies 199, 222, 314, 318, 561, 902
New books 561
Lumen, defined 643
Luminous efficiency of various light sources 559
Luminous flux defined 642
Luminous intensity defined 642
Luminous point-source 126
Lux, defined 643
Machine shop lighting (see Industrial lighting)
Mazda lamps (see Lamps)
Mercury-vapor lamps (see Lamps)
Mill lighting (see Industrial lighting)
Mirror, parabolic, theory of 905
Motion pictures, effect on the efficiency of the eye 491
SUBJECT INDEX XI
Newspaper plant lighting (see Industrial lighting) page
Nomenclature and standards 315, 555, 642
Office lighting 651
Downtown buildings 659
Semi-direct in the Edison building of Chicago 690
Specification for purchasing glassware for semi-indirect
fixtures 698
State, war, and navy department building 651, 659
Panama-Pacific Exposition :
Gas lighting 1083
Lighting 534
Parabolic mirror 005
Passenger boat and steamer lighting 680
Phot, defined 643
Photography :
Application of the new high efficiency tungsten lamps 149
Artificial illuminants, their uses in 947
Light sources 556
Submarine 403
Visual efficiency of various illuminants 03
Photometers: (See also Photometry)
Brightness 366
Compensated test-plate for illumination photometers 726
Errors of test-plates 729, 743
Maintenance of 774
Physical 101
Portable photometers 766
Portable, hints on use of 776
Photometry: (See also Illumination)
Approximate uniform point source 126
Arc lamps I
Books on 225
Colored light 717
Colored lights (see Heterochromatic photometry below)
Compensated test-plate for illumination photometers 727
Definitions 315
Flicker 259
a method of correcting abnormal color vision and its
application to the flicker photometer 551
Heterochromatic 551
application of Crova's to modern incandescent illumi-
nants 716
choice of a group of observers for measurements.... 203
experiments on colored absorbing solutions 253
Integrating sphere 1, 552
paint 31, 32
Xll TRANS. I. E. S. VOL. X
Photometry {continued) PAGE
Methods 3*5. 768
Of gas-filled tungsten lamps 553
Pentane, standard 554
Photo-electric cell 554
Practical hints on the use of portable photometers 766
Proposal as to methods and standards 315
bibliography 318
Purkinje phenomenon 575
Secondary standards 550
Standards 3*5
Theory of diffusion 373
Physical photometry IOI
Pilot flame ignition of incandescent gas lamps 670, 675
Piping:
Gas lighting (see Gas lighting)
Point-source :
Luminous 126
Projectors (see also Headlights) 271
Purkinj e phenomenon 575
Radiation 555
Specific luminous, defined 643
Ultra-violet (see Ultra-violet radiation)
Railway car lighting 82, 227, 546
Reflection :
Coefficients 399, 548
Diffuse (defined) 356, 364, 645
From inks and papers 383
From window envelopes 394
Interior furnishings 397
Parabolic mirror 905
Photographic papers 388
Regular, defined 645
Specular 353, 360
Total and mean (defined) 364, 370
Turbidity 364
Reflectors :
Functions and uses 631
Glass and metal compared 633
Maintenance 636
Recent developments 549
Rifle range lighting 749
Safeguarding the eyesight of school children 181
School lighting:
Safeguarding the eyesight of school children 181
SUBJECT INDEX Xlll
Searchlights: (See also Headlights) page
Recent developments 527
Semi-direct lighting: (See also Lighting)
Fixtures : •' 699. 7°°> 703
Office 6°o. °°7
Specification for purchase of glassware 608
Shop lighting (see Industrial lighting)
Signal lights 529, 53i
Spectrometer 300
Standards, primary, representative and working, defined 645
Steam lighting 68°
Street car lighting 82- 227> 546
Street lighting 405
Chicago, 111 281. 540
Classification of streets I04!
Color of light J034, 1057, 1060
Data on installations of various cities 1064
Data on street illuminants I050
Effective illumination of streets 1039
Gas
1080
High pressure gas 530, 1083
Influence of pavements I059» Jo02
Investigations 54s
Lamp posts, gas I0°2
Large versus small illuminants 1051
Mounting height of illuminants 1055
New York 541
Progress and installations in various cities 537
Silhouette effect I043
Size of lighting units and spacing intervals 1051
Uniformity of design of posts 1063
Swimming-pool lighting 754
Testing :
Lamps 8l4
Test-plates (see Photometry)
Textile mill lighting (see Industrial lighting)
Tungsten lamps (see Lamps)
Turbidity (see Reflection)
Type C lamps (see Lamps)
Ultra-violet radiation and the eye 932
Vision: (See also Eye)
Acuity and yellow light ioi6
Acuity in reading under lights of different color 1036
Animals 502
Brightness, its influence 985
Color 576, 577
XIV TRANS. I. E. S. VOL. X
Vision {continued) page
Color theories 259
Colors preferred 1036
Conditions for comfortable vision 988
Edridge-Green color theory 578
Effect of glare on 1006
Mechanical theory of 576
Phases of (see Eye)
Physical, physiological and psychic phases 562
Visual acuity (see Vision)
Window envelopes:
Tests for reflection, glare and contrast 394
Young-Helmholtz theory of color vision 576
INDEX TO AUTHORS.
The letter d indicates discussion.
PAGE
Alger, E. M. d— Light in the treatment of disease 144
Anderson, Earl A. d— Photometric measurements 783
Atkinson, A. A. d — Illuminating engineering education 344
Bailey, P. S. Incandescent headlights and projectors 271
Baldwin, Allen T. d— Street lighting 1067
Bancroft, Wilder D. The theory of cold light 289
Barrows, G. S. d— Illumination and accident prevention 879
d— Office lighting • 668
Barrows, W. E. d— Illuminating engineering education 346
Benford, Frank A., JR. The parabolic mirror 905
BenFord, F. A., Jr., and H. E. Mahan. A flux method of obtaining
average illumination 593
Black, Nelson M. A resume of the physical, physiological and
psychic phases of vision 5°2
d— Efficiency of the eye "39
Bond, C. O. d— Light in the treatment of disease 144
Bostock, Edgar H. Sheet glass in lighting 1086
Brinckerhoff, Frank M. d— Railway car lighting 249, 250
Burge, W. E. Ultra-violet radiation and the eye 932
Burrows, Robert P. Small incandescent lamps and special illumina-
tion problems ll7l
Burrows, S. B. d— Selling illumination 7*5
Cady, F. E. d— The integrating sphere, accuracy and use 33
Cassidy, George W. Art and science in home lighting 55
Chadbourn, R W., A. E. Kennelly and G. D. Edwards. An ap-
proximate uniform photometric point-source 126
Chamberlain, G. N. d— Street lighting 1078
Chaney, N. K., and E. L. Clark. Notes on the integrating sphere
and lamp photometry J
Chapman, W. E. Artificial lighting of typical offices in the state,
war and navy department building 651
Chillas, R. B. d— The integrating sphere 34
Clark, E. L., and N. K. Chaney. Notes on the integrating sphere
and lamp photometry *
CLEWELL, C. E. Illuminating engineering as a branch of technical
instruction 321
Cobb, Percy W. d— Light in the treatment of disease 143
d — Test for efficiency of the eye "44
Committees on Lighting Legislation and Factory Lighting 1184
Committee on Glare. Reports 353, 366, 379, 388, 394, 397, 987, 1000
xvi TRANS. I. E. S. VOL. X
PAGE
Committee on Nomenclature and Standards of the Illuminating
Engineering Society. (191 5 Report) 642
Committee on Progress. Report 5*5
Cravath, J. R. Knowns and unknowns in the lighting of small
interiors 303
d— Brightness and glare in office lighting 7*3
d — Automobile headlights 921
d— Efficiency of the eye 1130, H33, "39
Crittenden, E. C, E. B. Rosa and A. H. Taylor. Effect of atmos-
pheric pressure on the candlepower of various flames. . . 843
Dicker, Alfred O., and James J. Kirk. Lighting in downtown office
buildings °59
Doane, L. C. Modern street car lighting 82
Durgin, W. A. d— Use of portable photometers 779
d — Color preference I030
Durgin, W. A., and J. B. Jackson. Semi-direct office lighting in the
Edison building of Chicago 690
Edwards, G. D., A. E. Kennelly and R. W. Chadbourn. An ap-
proximate uniform photometric point-source 126
Ely, R. B. d— Light in medical practise 145
Evans, W. A. D. d— The mercury-vapor lamp in photography 170
Industrial lighting with mercury-vapor lamps 883
FERREE, C. E-, and Gertrude Rand. The efficiency of the eye under
different conditions of lighting 407
Further experiments on the efficiency of the eye under differ-
ent conditions of lighting 448
Some experiments on the eye with inverted reflectors of differ-
ent densities I097
Flowers, Alan E. d— Illuminating engineering education 347
Gage, H. P. d— Parabolic mirror and automobile headlights 926
d — Infra-red radiation 944
Gilpin, F. H. d— Candlepower of gas flames 864
Gove, W. G, and L. C. Porter. A practical study of car lighting
problems 227
Harrison, Ward, d— Photometric reading errors 742
Haskell, Raymond. Lighthouse illumination 209
Haynes, Pierre E. Street lighting in Chicago 281
Hibben, S. G. d— Street car lighting 99
d— School lighting 201
d— Railway car lighting 246
Hoadley, George A. d— Photography, lenses and plates 178
Hodgson, M. B., L. A. Jones and Kenneth Huse. Relative photo-
graphic and visual efficiencies of illuminants 963
Hunter, G. H. d— Home lighting 76
Hurley, W. P. Street lighting with modern arc lamps 405
INDEX TO AUTHORS XV11
PAGE
Huse, Kenneth, M. B. Hodgson and L. A. Jones. Relative photo-
graphic and visual efficiencies of illuminants 963
Hutchinson, F. R. Gas street lighting 1080
Hyde, E. P. d— Automobile headlights 922
d — Ultra-violet radiation 943
HvER, Z. M. d— Selling lighting service 806
d— Combination gas and electric lighting systems 809
Ives, Herbert E. Physical photometry 101
Proposals relative to definitions, standards and photometric
methods 3*5
Ives, Herbert E., and Edwin F. Kingsbury. On the choice of a
group of observers for heterochromatic measurements . . 203
Additional experiments on colored absorbing solutions for use
in heterochromatic photometry 253
A method of correcting abnormal color vision and its applica-
tion to the flicker photometer 259
The application of Crova's method of colored light photometry
to modern incandescent illuminants 716
Jackson, Dugald C. d— Street lighting 1060
Jackson, J. B., and W. A. Durgin. Semi-direct office lighting in the
Edison building of Chicago 690
Johnson, H. M. Some recent experiments on vision in animals 502
Jones, L. A., M. B. Hodgson and Kenneth Huse. Relative photo-
graphic and visual efficiencies of illuminants 963
Jordan, C. W. d — Errors in integrating sphere readings 35
Pilot flame ignition of incandescent gas lamps 670
Junkersfeed, Peter, d — Street lighting 1066
Kenneley, A. E., R. W. Chadbourn and G. D. Edwards. An ap-
proximate uniform photometric point-source 126
Kingsbury, Edwin F., and Herbert E. Ives. On the choice of a
group of observers for heterochromatic measurements.. 203
Additional experiments on colored absorbing solutions for use
in heterochromatic photometry 253
A method of correcting abnormal color vision and its applica-
tion to the flicker photometer 259
The application of Crova's method of colored light photometry
to modern incandescent illuminants 716
Kirk, James J., and Aefred O. Dicker. Lighting in downtown office
buildings 659
Lacombe, Charees F. d— Street lighting 1073
Lancaster, Walter B. d— The efficiency of the eye 1140
LEPAGE, C. B. d— Illuminating engineering education 350
LEWinson, L. J. d— Photometry of electric incandescent lamps 837
Litle, T. J., Jr. d— Gas pilots 678
d— Combination gas and electric lighting systems 808, 810
XV111 TRANS. I. E. S. VOL. X
PAGE
Uttle, W. F. d — Integrating sphere, accuracy 28
Practical hints on the use of portable photometers 766
Little, W. F., and Clayton H. Sharp. Compensated test-plate for
illumination photometers 727
LiTTLEFiELD, C. A. d — Education of lighting solicitors 805
Luckiesh, M. d— Home lighting 73
The application of the new high-efficiency tungsten lamp to
photography 149
Safeguarding the eyesight of school children 181
d — Application of the tungsten lamp in photography 956, 983
Yellow light 1015
McAllister, A. S. Simplification of illumination calculations 587
Macbeth, Norman, d — Illuminating engineering education 341
d — Photometric readings and equipment 785
d — Selling lighting service 807
d — Automobile headlights 928
Magdsick, H. H. d— Street lighting 1064
Mahan, H. E., and F. A. Benford, Jr. A flux method of obtaining
average illumination 593
MEES, C. E. K. d — Use of the tungsten lamp in photography 173
d — Testing electric incandescent lamps 841
d — Automobile headlights 920
Artificial illuminants for use in practical photography 947
Middlekauff, G. W. d — The integrating sphere, screens ; paint . . 32, 33
Middlekauff, G. W., B. Mulligan and J. F. Skogland. Life test-
ing of incandescent lamps at the Bureau of Standards . . 814
Millar, Preston S. d — Illuminating engineering education 342
d — Errors of photometric test plates ; photometric data 744, 787
d — Lighting company service 802
d — Testing electric incandescent lamps 839
The effective illumination of streets 1039
Minick, J. L. d — Photometry of electric incandescent lamps 839
d — Locomotive headlights 919
Mortimer, J. D. d— Street lighting 1069
MoTT, W. R. d — Light in the treatment of disease 147
d — Ultra-violet radiation 939
d — The flame arc lamp in photography 959, 960
MouLTON, W. R. d — Lighting of passenger boats 688
d — Lighting company service 804
d— Street lighting 1061
Mulligan, B., G. W. Middlekauff and J. F. Skogland. Life test-
ing of incandescent lamps at the Bureau of Standards.. 814
Nichols, G. B. d — Armory lighting 760
d — Combination gas and electric lighting systems 810
Nordstrum, L. D. d — Street lighting 1068
INDEX TO AUTHORS XIX
PAGE
Oday, A. B. and A. L. Powell. Present practise in the lighting of
armories and gymnasiums with tungsten filament lamps 746
Owens, H. Thurston, d— Sale of semi-indirect fixtures 715
Piatt, F. C. d— Street lighting 1070
Pierce, R. ff. d — Design of fixtures and glassware 713
Porter, L. C. New developments in the projection of light 38
d — Home lighting 75
d — Passenger steamer lighting 688
d — Gymnasium lighting , 762
d — Photometric measurements 781
d — Combination gas and electric lighting systems 809
d — Automobile headlights 924
d — Uses of miniature electric incandescent lamps.. 1182
Porter, L. C, and W. G. Gove. A practical study of car lighting
problems 227
Potter, N. H., and A. B. Spaulding. How can gas and electric
companies under one management render the best light
service ? 793
Powell, A. L. d — Home lighting 70
Powell, A. L., and A. B. Oday. Present practise in the lighting of
armories and gymnasiums with tungsten filament lamps 746
Priest, I. G. d — Ultra-violet radiation 942, 944
Pratt, W. H. d— Street lighting 1065
Rand, Gertrude, and C. E. Ferree. The efficiency of the eye under
different conditions of lighting 407
Further experiments on the efficiency of the eye under different
conditions of lighting 448
Some experiments on the eye with inverted reflectors of differ-
ent densities 1097
Regar, G. Bertram, d — Lighting company service 880
Richtmyer, F. K. d — Illuminating engineering education 349
Rolph, T. W. d — Railway car lighting 245
d — Illumination and the eye 1 132
Rosa, E. B. d — Candlepower of pentane lamps 865
Rosa, E. B., E. C. Crittenden and A. H. Taylor. Effect of atmos-
pheric pressure on the candlepower of various flames. . . 843
Rose, S. L. E. d — Measuring light dispersed by jewels; the inte-
grating sphere, accuracy 31, 32
d — Recording photometric data 783
Rowland, Arthur J. d — Illuminating engineering education 343
SCHERESCHEWSKY, J. W. d — Ultra-violet radiation 941, 945
d — The eye and lights of different colors 1033, 1036
d — Tests for eye efficiency 1131
Scott, Charles F. d — Illuminating engineering education 338
Serrill, William J. d — Illuminating engineering education 340
XX TRANS. I. E. S. VOL. X
PAGE
Sharp, Clayton H. d — The integrating sphere 28, 35
Some data on artificial daylight units 219
d — Illuminating engineering education 348
Sharp, Clayton H., and W. F. Little. Compensated test-plate for
illumination photometers 727
Simpson, R. E. d — Illuminating engineering education 345
Illumination and one year's accidents 868
Skogland, J. F., G. W. Middlekauff and B. Mulligan. Life test-
ing of incandescent lamps at the Bureau of Standards.. 814
Spaulding, H. T. The lighting of a passenger steamer 680
Spaulding, A. B., and N. H. Potter. How can gas and electric
companies under one management render the best light
service ? 793
Steinmetz, Charles P. d — Effect of color of light on sight 1036
Stephens, C. E. d— Street lighting 1078
Stickney, G. H. d— Home lighting 79
d — Railway car lighting 248
d— Office lighting 668
d — Photometric test-plates 744
d — Photometric errors 783
d — Effects and application of lights of different colors 1034
d— Street lighting 1058
Sterrett, H. R. Piping houses for gas lighting 296
Taylor, A. H. d — Photometric errors 789
Taylor, A. H., E. C. Crittenden and E. B. Rosa. Effect of atmos-
pheric pressure on the candlepower of various flames. . . 843
Titus, E. C. Some uses of light in the treatment of disease 135
Vaughn, F. A. d — Combination gas and electric lighting systems. . . 810
Whitehead, John B. d — Street lighting 1065
Williamson, J. E. Submarine photography 403
TRANSACTIONS
OF THE
Illuminating Engineering Society
Vol. X
NUMBER 1 1915
NOTES ON THE INTEGRATING SPHERE AND ARC
LAMP PHOTOMETRY.*
BY N. K. CHANEY AND E. L. CLARK.
Synopsis: After a brief historical introduction, the paper undertakes
an exhaustive analysis of the characteristics of the integrating sphere,
with special reference to the asymmetry in integrating properties arising
from the necessary introduction of screens and opaque bodies. A mathe-
matical expression is developed for the error of integration, which con-
tains factors depending upon the reflecting power of the sphere walls;
upon the relative size and position of the screen with respect to the light
source, and to the photometric window ; and upon the distribution of the
light flux from the sources under comparison. Experimental data veri-
fying the general theoretical conclusions are given. An earlier paper on
this subject is criticized, particularly the statements regarding the use
of translucent screens, and the measurement of extended light sources.
The conclusion reached is that translucent screens are not desirable and
that extended light sources of sizes now common among modern arc
lamps do not give erroneous values when measured in a properly designed
sphere. A summary of the conditions which should be maintained in a
sphere' to secure accuracy is given. The method used in the photometrical
laboratory of a large manufacturing company for comparing various
carbons used in a variety of lamps is described. A rational method of
proportioning the measurements made upon a single trim to the number
of trims measured is given.
The integrating sphere has received relatively less attention at
the hands of American investigators than that accorded it abroad.
Among the more important contributions to our knowledge of the
sphere in this country is the paper read before this society by
Sharp and Millar in 1908.1 The latter contains an excellent il-
lustrated description of integrating spheres and their equipment
together with an account of the special advantages offered by their
use. It is unfortunate, however, that in the limited space at their
disposal the authors felt obliged to deal so briefly with the theo-
retical aspects of the subject, and that they failed to indicate the
more exhaustive treatment to be found in the original literature.
* A paper read at the eighth annual convention of the Illuminating Engineering
Society, Cleveland, O., September 31-24, 1914. . .,, „ofltc _,
The Illuminating Engineering Society is not responsible or the statements or
opinions advanced by contributors.
1 Trans. I. E. S., vol. Ill, p. 502.
2 TRANSACTIONS I. E. S. — I'ART 1
The present paper suffers somewhat from the same defect.
No pretense is made of giving an adequate resume of the vol-
uminous German articles upon the subject. Owing to the long
delays experienced in securing the original papers, the work here
reported took its point of departure from the above-mentioned
paper of Sharp and Millar. Theoretical developments which
differ somewhat in form from the German were followed inde-
pendently.
A brief historical survey shows that the earliest forerunner
of the spherical integrator was the "lumen-meter" of Blondel, in
1895. Three forms are mentioned in which the light source was
placed in the center of an opaque sphere, through which light
could leave from one or more openings and after a certain num-
ber of reflections be thrown upon a screen and photometered.
Its application was limited to axially symmetrical light sources.
The Matthews integrating mirrors designed in 1901 suffer
from the same limitation, unless the radially asymmetrical light
sources can be rapidly rotated.
The fundamental theorem of the modern spherical integrator,
was first mathematically developed by an Englishman, Sumpner,
in the Philosophical Magazine in 1893. He stated that "any
bright patch on the inner surface of a diffusely reflecting sphere
illuminates each part of the sphere to the same extent". It fol-
lows conversely that any area upon the inner surface of such a
sphere is illuminated by all of the other bright patches pro-
portionally to their brightness only, and irrespective of their
position. In other words any given area is illuminated propor-
tionally to the average illumination of the rest of the sphere.
Sumpner, however, overlooked the practical application of his
theorem to integration of asymmetrical light sources until after
Ulbricht in 1900 had independently derived the same theorem
and applied it to the determination of the mean spherical candle-
power of light sources by a single measurement.
The Ulbricht integrator, as is well known, consists of a hollow
sphere with a white diffusely reflecting coating and having in its
wall a small opening or photometric window. The light source
is placed in the sphere and a small screen placed between it and
the photometric window or test plate, so that the latter receives
CHANEY AND CXARK : ARC LAMP PHOTOMETRY 3
no light directly from the source, but only that reflected to it
from the walls of the sphere. The average illumination upon
the walls is proportional to the total light flux and by Sumpner's
theorem2 the illumination of the test plate area would be exactly
proportional to the average illumination of the sphere wall, that
is, to the total light flux, except for one fact, viz., the introduc-
tion of the opaque screen into the sphere.
It is evident that the variable direct light flux must be screened
from the test plate windows, otherwise the test plate will re-
ceive an amount of light varying with the position and distribu-
tion of the source. It is also evident that the presence of the
necessary screen invalidates the rigorous application of the
fundamental theorem of light integration which we have just
been considering.
Sumpner's theorem is valid only for an empty sphere. The
theorem does not state that all parts of the sphere wall
are equally illuminated, for this is contrary to fact with asym-
metrical light sources. Therefore if the test plate window is to
receive an illumination exactly proportional to the total light
flux, it must receive light from the entire sphere wall. This will
be prevented by the presence of screens or opaque bodies of any
kind.
The effect of a screen is not only to prevent a certain portion
of the direct light flux from reaching the sphere wall, but also to
screen an opposite part of the sphere wall from the test plate.
The resulting situation is readily seen by the screen and sphere
diagram, as shown in Fig. I, A and B.
The effect of the screen is to divide the sphere into three zones
or areas as shown in Fig. i, B. Each of these three zones
possesses different physical characteristics. Zone I is not visibly
distinct from Zone II. It is the part of the sphere wall con-
cealed by the screen when observation is made through the test
plate window at C. The direct light flux falling upon Zone I
•- Mathematical proof of Sumpner's theorem.— Assuming the validity of Lambert's
cosine law the illumination, E, which any infinitesimal area, AA, will receive from any
other similar area of brightness, e, is expressed as follows :
47rr-
With a given sphere radius this expression contains no variable except the brightness of
the patch e, and hence is independent of its distance or position.
4 TRANSACTIONS I. K. S. — PART I
cannot directly illuminate the test plate at C, but must suffer an
additional reflection before reaching the test plate.
Zone III is visible when the sphere is in operation. It is the
projection on the sphere wall of the shadow of the screen. It
measures the solid angle of the direct flux intercepted by the
screen. The flux falling upon the screen (as measured by Zone
ZonelZ. (/nscreenet/
Zone!
Screened f
Fig. i. — Screen and sphere diagram.
Ill) must be first reflected to the central zone before it can
contribute to the illumination at the test plate. Thus Zones I
and III comprising the "screened areas" both differ from the
"unscreened" central area or Zone II, in a like manner. That is,
the light flux directed towards either of the "screened areas"
must suffer one additional reflection, and consequent loss by ab-
sorption, in comparison with the light flux falling upon the "un-
screened" central zone. The latter alone possesses the char-
acteristics required for perfect integration. All of the flux upon
Zone II contributes in direct proportion to the illumination at
the test plate C.
CHANEY AND CLARK: ARC LAMP PHOTOMETRY 5
The spherical integrator is not therefore a theoretically per-
fect instrument. It cannot be so designed as to integrate per-
fectly every conceivable type of light flux regardless of the dis-
tribution of the latter in the sphere. It may be so designed,
however, as to reduce the error to any desired limits. With this
fact clearly in mind it evidently becomes necessary to inquire
very exactly into the limitations and characteristics of the spheri-
cal integrator.
The mathematical treatment here employed, although devel-
oped independently, is in some respects substantially similar to
the earlier work of Ulbricht but is less complicated in form and
leads to simpler generalizations. The problem is treated in part
graphically and in part by a few general considerations from
which may be deduced a characteristic mathematical expression
for the integrating properties of the sphere.
As shown by Sumpner the walls of any enclosure possess an
illumination much greater than that corresponding to the inten-
sity of the original light flux. When light falls upon a reflecting
surface, part of it is absorbed and part is reflected, the relative
amounts depending upon the absorption coefficient a and the
reflection coefficient p whose sum is unity.
The total illumination on the sphere wall I, is thus made up
of two parts :
(i) The direct illumination from the light source ld, (2) plus
an infinite number of reflections from the walls or the reflected
illumination Ir
I = Irf+ I, (1)
or
l = Id+pld + P'ld + ...+ P{"-l)^= ^[^^ ■
Hence
1=-^- =^ (2)
I — p a
or
I = Irf + pi (3)
and
I =al + Pl (4)
The ratio of the direct illumination to the total is thus given by
6 TRANSACTIONS I. E. S. PART I
the absorption coefficient, and the ratio of the reflected illumina-
tion to the total is given by the reflection coefficient.
Now the direct illumination of average value I,/, varies in
intensity at different parts of the sphere according to the dis-
tance and degree of asymmetry of the light source. Its average
amount is 20 per cent, of the total illumination I, for the usual
value of the absorption coefficient, a is about 0.2.
The reflected illumination pi, usually amounting to 80 percent,
the average total illumination, is equal in all parts of an empty
sphere.
Therefore the direct illumination from the light source, Id, is
screened from the test plate in order to measure the reflected
illumination, pi.
The presence of the screen, however, destroys the uniformity
of the illumination pi so that its true or average value is no
longer identical with the apparent value at the test plate.
The source of error in integration thus depends upon the man-
ner and extent to which the reflected illumination as actuall)'
read at the test plate, differs from the theoretical value of
the reflected illumination pi for an empty sphere. Any constant
difference between the observed and the theoretical values of pi
will be corrected by the substitution method of determining the
"sphere constant" with a standard lamp, and therefore may be
ignored. But variable differences, dependent in an)' manner
upon the character or position of the light source can not be so
corrected and constitute a source of error the magnitude and
characteristics of which must be known.
II the reflected light pi be separated into two components it
will be found that one component depends upon the light flux in
a constant manner, and the other in a variable manner.
From equation (3) multiplying through by p gives an ex-
pression for the two components of pi
pi - plrf -f p2I (5)
That is the reflected illumination consists of the first reflection,
pld, of the direct illumination ldt plus the sum of the succeeding
multiple reflections p'l.
Since all reflections after the first are assumed to be completely
diffused by the character of the surface of the sphere, the com-
ponent p2I is independent of the character or degree of asymmetry
CHANEY AND CLARK: ARC LAMP PHOTOMETRY J
of the original surface illumination by direct light. It will.
however, suffer a slight constant reduction, due to the absorption
of the diffusely reflected light by the surface of the screen. The
component p1! amounting to 80 percent, of pi (ifp = o.8) is
therefore subject to perfect correction in the "sphere constant/
The case is different, however, in the first component of
pi which consists of the first reflection pl^ of the direct illumi-
nation Id.
The position upon the surface of the sphere on which the
illumination ld exists, determines whether any part of its first
reflection p\d will reach the test plate or whether the illumina-
tion at the test plate will consist only of the subsequent reflec-
tions Kp2I (6)
A glance at Fig. 1 shows that if the direct light flux falls
entirely upon the central area (Zone II) the first reflection
pld will be represented at the test plate C.
That is, the observed illumination at the test plate is
V =pld+ KpJI (7)
But if the direct light flux falls entirely upon the screened
areas (Zones I and III)4 the component due to the first reflection
pld will be intercepted by the screen, and the observed illumina-
tion at the test plate is
T = KVI (8)
The maximum difference in the illumination I' due to asym-
metry of light flux is therefore equal to pld, or is the fraction
plrf
—=- = a, of the theoretical reflected illumination pi of an empty
sphere ( 9 )
If 8 = fraction of total direct light flux falling upon the screened
areas, then the actual illumination at the test plate from the
component plrf is (1 — 8) pld. Hence the fraction of pi read at
the test plate is
T __ (1— 8)plrf + Kp'I
Pi Pl
(1 — S)a - Kp (10)
5 If K = fraction of p2I uot absorbed, the illumination at the test plate is Kp*I for the
second component (6)
K is almost unity if the screens are small compared with the surface of the sphere.
* The light flux falling upon the screen is measured by Zone III. Hence Zones I and
III may be treated in the same manner.
8 TRANSACTIONS I. K. S. PART I
The actual error of integration, E, not compensated by the
standard lamp method of determining the "sphere constant" is
equal to the difference between the fraction of pi read at the test
plate with the unknown lamp, and that read with the standard
lamp.
If 8' = fraction of direct light flux falling upon screened areas
with standard lamp and
8 = fraction of direct light falling upon screened areas with
unknown lamp, then
E= [(i— 8)a + Kp]-[(i-8>+Kp]=o(8'-8)..(xi)
As 8' and 8 are coefficients representing fractions of light flux
they may be expressed in terms of illumination and area.
Let
Sum of screen areas ,
o- = -r : , and
Total area
Direct av. illumination on screened area
Direct av. illumination on total area
then
8' = a6' for standard lamp
and
8 = ad for unknown lamp.
Hence
E = a<r(0' — 0) (12)
Equations (n) and (12) are the most general forms of the
mathematical expression for the integrating error of the sphere.
Space does not permit a detailed account of all of the interesting
characteristics of the spherical integrator as shown by this ex-
pression.
It is obvious, however, that the error of integration increases
with the magnitude of the absorption coefficient, with the size of
the screened areas relatively to the total area, and with the dif-
ference in the relative illumination of the screened areas by the
standard lamp and the unknown lamp, and that the error is zero
only when the average distribution of light flux upon the screened
areas is the same for standard and unknown lamps.
CHANEY AND CLARK: ARC LAMP PHOTOMETRY 9
Since 8, or 6 (that is, the ratio of flux or illumination respec-
tively) depends upon the distance of the sources from the
screened areas, the relative positions of the standard lamp and
unknown lamp as well as their distribution curves must be con-
sidered before assuming that the error is necessarily zero when
the standard and unknown lamps have the same distribution, or
is greater than zero if two sources have unlike distribution.
Our general equation shows the error of Presser's suggestion
that a grey wall with an absorption coefficient of 0.5 would give
better results than a lower value of 0.2. The argument advanced
was that the higher absorption coefficient suffered less change by
reason of the collection of dust and dirt upon the sphere walls.
While this is true, the remedy is not to allow the walls to become
dirty, rather than to attempt to match the dirt by the initial color
of the sphere. The change suggested more than doubles the in-
tegrating error.
Ulbricht also states that a large absorption coefficient causes
greater deviation from the cosine law, and lessens the range of
the sphere for lights of low intensity.
Further, the general equation shows that the error of inte-
gration may be decreased by decreasing the size of the screened
areas or Zones I and III shown in Fig. 1. An inspection of the
diagram shows that if a point source be situated in the center of
the sphere the screened area (afe) or Zone I will be a maximum
when the screen, S, is nearest the test plate C, while the screened
area (bed) will be a maximum when the screen is nearest to
the light source L.
At some intermediate position, the sum of these two screened
areas will therefore be a minimum.
This minimum position may be graphically determined by
drawing diagrams of the intermediate positions upon plotting
paper, and noting at which position of the screen the sum of
the two lines / hf and h c are a minimum. Ulbricht has devel-
oped general mathematical expressions for the stun of these two
areas and the conditions for which they are a minimum. He
finds that the horizontal distance of the screen from the center
of the sphere should be 0.39 X R, if R = radius of sphere, and
IO TRANSACTIONS I. E. S. PART I
the light source is at the center.5 If the light source be above
the center making an angle of 35 ° with the test plate and the
horizontal, the value is smaller, about 0.29 X R, the screen
being elevated proportionally. (This design is advocated by
several German writers, especially for arc lamps with a large
lower hemispherical light flux). In general, however, a value
of 0.4 X R may De accepted as the best distance between lamp
and screen.
Having placed the screen in the position for minimum area
of Zones I and III, this area may be further decreased only by
increasing the size of the sphere, since the size of the screen is
determined by the area of the largest light sources to be meas-
ured, or by the cross section of the largest diffusing globes em-
ployed. The largest permissible ratio between the screen and
sphere diameters must be arbitrarily determined by the limits of
error within which it is desired to work.
Ulbricht estimates that the cross section of the sphere must
be at least twenty times the cross section of the screen, or with
circular screens the diameter of the sphere must be over 4.5
times the diameter of the screen. In this case the sum of the
screened areas is 20 per cent of the sphere area for a point
source in the center of the sphere. Therefore, with a sym-
metrical light source 8 = 0.2 and the reflected illumination at
the test plate is diminished by the fraction
0.2pl
— 0.2a = 4 per cent, if a = 0.2 (10)
Pi
The error, however, by the general equation (10) is
E = a<r(0' — 0) = 4 per cent. (0' — 0)
in which ($' — 6) may have values of from o to 5 respectively.
6 ^z — . If the light flux from the standard lamp is
o- 0.2
B Some latitude is possible since small changes in the screen position are partly com-
pensating in their effect upon the magnitude of the screened areas.
Chillas has calculated that with a screen diameter one fifth of the sphere diameter
the position for minimum screened areas is at the distance 0.372R from the sphere center,
in which case the magnitude of the screened areas is 15.0 percent, of the sphere area.
The ratio of the area of Zone I to the area of Zone III is 3 to 2 for minimum areas.
For screened areas of equal size the distance of the screen from the center is about
0.315R ond the sum of the screened areas is 15.6 percent, of the sphere area, an increase
in the screened areas but 0.6 per cent, over their minimum value.
CHANEY AND CLARK: ARC LAMP PHOTOMETRY II
approximately symmetrical, 6' = i and therefore 6, the ratio of
the average direct illumination upon the screened areas to the
average direct illumination on the sphere wall as a whole, must
be not less than 0.75 or greater than 1.25 if the error of in-
tegration is to be not more than 1 per cent. Since 6 may quite
easily vary from 0.5 to 2.0 giving an error of 2 to 4 per cent, it
would seem that the ratio between screen and sphere diameters
selected by Ulbricht is much too large even as a maximum, if the
error is to be kept below 1 per cent, for light sources of very
different types of distribution. The 80-inch sphere requires a
screen of but one sixth the diameter of the sphere and the
screened areas are but 12 per cent, of the total area. This cuts
down the above limits of error nearly one half.
In arc lamp photometry a further source of complication is
that the standard lamp must be read while the unlighted arc
lamp is in the sphere in order to correct for the absorption of
light by the lamp parts and the screening effect which it has as
an opaque body.6
A second screen (s' in Fig. 2) is therefore required which
Fig. 2.— Two-screen diagram.
screens another part of the sphere wall (a' e' /') from the test
plate. This screen s' may be quite small as the standard lamp
filaments need not require a large screen. Fig. 2 shows, how-
ever, that if the lamp be moved from the position 1/ to L the
relative amount of total light flux falling upon the two screened
6 Any opaque body acts in two ways to diminish the illumination at the test plate.
It absorbs an amount of light proportional to its surface area and the absorption coeffi-
cient of its surface, and it screens a part of the sphere wall from the test plate, depending
upon its shape and relative position in the sphere.
I J TRANSACTIONS I. E. S. — PART 1
areas (a c f) and (a' e' /') will alter with the change in the
relative distances from the areas. The position and size of the
screen, s', must be so chosen, therefore, that the relative screened
areas (b d c) and (b' d' c) at the test plate will be in compen-
sating ratio. As Ulbricht has shown, if the light sources have
a pronounced asymmetry the relative flux in the different direc-
tions must be determined from the distribution curves of the
lamps and corrected for.
This is obviously unsatisfactory, and the rational correction
is therefore to construct spheres of sufficient size to make the in-
fluence of the screened areas small and the effect of their rela-
tive proportions negligible. In other words if <r, in the general
equation
E = «r(0' — 0)
is not greater than i/io, the screen errors may be neglected for
light sources of ordinary distribution.
Before considering the case for extremely asymmetrical
sources, it will be convenient to derive a special form of the
general equation applicable when the standard lamp has a dis-
tribution sufficiently symmetrical to give the same average direct
illumination upon the screened areas as upon the unscreened
area. In this case
8' = o-
and
E = a(S' — 8) = a(<r — 8) (13)
Since both a and o- are known or may be determined for any
given sphere, the error becomes a constant multiplied by but one
variable factor depending upon the distribution of the light flux
of the unknown lamp.
For example with the 80-inch (2.03 m.) integrating sphere in
this laboratory
a = 0.2 approx.
a- = 0.1 approx.
Hence
Per cent. E = 0.2 X (0.1 — 8) X 100.
8 may have any value from zero to unity.
If S = o.o, then E = 2 per cent.
If 8 — 0.1, then E = o per cent.
If 8 = 0.2, then E = —2 per cent.
If S = 1.0, then E = —18 per cent.
CHANEY AND CLARK : ARC LAMP PHOTOMETRY
13
While the maximum possible error is very large it should be
noted that the conditions for its occurrence are very unlikely to
happen except by design.
The expression E = a(<r — 8) has two maxima (-fa) and ( — a).
In practise, however, o- is never greater than 0.25, hence the
maximum of (-fa) has no practical significance. The condition
that E, approach ( — a) is that o- be very small and 8 be unity;
since 8 = a9, however, 8 usually decreases with a instead of be-
coming a maximum. In order for 8 to be unity when o- is small
all of the light flux must be concentrated upon certain very small
portions of the sphere area. In the numerical values quoted for
the 80-inch (2.03 m.) sphere <r = o.i. Therefore if the total
direct light flux should be so asymmetrical as to illuminate but
one tenth of the area of the sphere and if the direction of the
rays were left to chance, the probabilities are 10 to 1 that none
instead of all of the direct light would fall upon the 10 per cent,
of screened areas, that is 8 would be o instead of unity, giving
an error of +2 per cent, instead of — 18 percent.
Furthermore it so happens that the screened areas are divided
0/ re eft on of
l/f/>rf7ux
PAofo metric
Fig. 3. — Diagram for hemispherical distribution.
and occupy opposite sides of the sphere which renders them
still less likely to receive the entire flux of extremely asymmetri-
cal sources. This is well illustrated by Ulbricht's classic experi-
ment of rotating a lamp in the sphere one side of which was
covered with black paint. Thus a light source having an ap-
proximately hemispherical distribution was obtained. In a
20 inch (50.8 cm.) sphere, values were obtained as shown
in Fig. 3.
The light flux is directed toward the screen and then is given
14 TRANSACTIONS I. K. S. — PART 1
successive 900 turns. The readings indicate a very high degree
of integrating capacity for so small a sphere.
If the same experiment be performed in a properly con-
structed 80-inch sphere no appreciable difference in the various
directions of a hemispherical light source can be detected. An
examination of the diagrams will show, however, that the suc-
cess of the experiment depends upon the relative position of the
two screened areas upon opposite sides of the sphere. Assum-
ing that the two screened areas are approximately equal then for
each position half of the screened areas are in the shadow of
the lamp, and half are illuminated. Therefore, 6, the ratio of
direct illumination upon screened areas to the direct illumination
upon the sphere as a whole is always equal to 1 and the error of
integration is zero [E - a<r(i — 6)1 for all positions of the
hemispherically asymmetrical source. The same holds true
whether the lamp be rotated upon the horizontal or perpendicu-
lar axis. This compensation by position, however, holds only
for hemispherically asymmetrical light sources.
If the distribution curve of the lamp has two horizontal
maxima such as is caused by heavy side arms in some types of
arc lamp, then both screened areas might receive the maximum
flux in one position of the lamp and both would receive the min-
imum for a rotation of 900 . To map out the real character-
istics of the screened and unscreened zones, a much more asym-
metrical light source is required which will directly illuminate
a fraction of the sphere wall smaller than either of the two
screened areas.
An examination was made in this manner of the 80-inch
(2.03 m.) metal sphere and an 80-inch wooden, box integrator
having an inner surface in the form of an 18-sided polyhedron.
A large tungsten lamp of about 160 mean spherical candle-
power was entirely covered with black paper except for one
opening of about 2 inches (5.08 cm.). When this was directed
toward either of the two screened areas no direct light fell upon
the unscreened area. Three positions on the central area were
also chosen, so that no direct light fell upon either of the screened
areas. The photometric readings are placed in ratio with the
900 reading = 100.
It is seen that in the case of the sphere very good agreement
CHANEY AND CLARK: ARC LAMP PHOTOMETRY
15
is obtained for the three positions (450, 900 and 1350) upon the
central zone, or unscreened area. The same positions for the un-
screened area of the box show greater asymmetry due to the
deviation from the spherical form but considering the concen-
tration of the light flux the variation of 2.5 per cent, is sur-
prisingly low.
On the other hand the values for the positions, 0° and 1800,
on the two screened areas, or Zone III and Zone I respectively,
show a large drop of approximately 25 per cent, for both the
box and the sphere. These values represent the maximum var-
iations possible in the reflected illumination at the test plate and
are of the known order of magnitude of the absorption coef-
ficient a, in agreement with the theoretical deduction. (See
Equation 9.)
O/recf/on of ' .
/•3S'
/ao'
Sp/tere
72
'OOJ
/oo
/oaj
76S
Box
77*
S7.5
/OO
S7.f
74
Fig. 4.— Diagram for concentrated flux.
In fact with certain refinements this provides a simple method
for determining the absorption coefficients of the sphere wall or
of the screen.
It is evident from the foregoing work that extremely asym-
metrical light sources may be accurately integrated in a well
designed sphere if the precaution is observed to direct the flux
entirely upon the central zone. The slight error is easily cor-
rected in two ways. First, if the standard lamp gives the same
average illumination upon the screened area (a e f) in Fig 1 as
upon the rest of the sphere the error is then E = ao- in which
both a and <r are known or can be easily determined. Second, a
standard lamp which also throws its entire flux upon the central
zone may be employed. Then E = a(S' — 8) = o since both 8'
and 8 are zero.
It has been shown that the conditions for perfect integration
l6 TRANSACTIONS I. E. S. PART I
are, (i) a small absorption coefficient of the sphere walls;7 (2)
the smallest possible percentage of the sphere wall screened from
the test plate and from the direct rays of the lamp; and (3), a
similar ratio of the light flux upon the screened and unscreened
portions of the sphere wall for both the standard lamp and the
unknown lamps.
It has been shown from the form of the general equation for
integration error
H = acr(0' — 0)
that the more closely the first two conditions are approached,
the greater may be the deviation from the third condition with-
out serious error, while on the other hand if the third condition
be exactly fulfilled the first two conditions may be entirely
ignored.
Finally it has been shown that with exceedingly asymmetrical
light sources the possible error is small if the most intense por-
tion of the flux is always directed away from the screened areas,
and upon the central zone of the sphere (i. e., if 6 is kept equal
to or less than 1 ) .
The remainder of the paper will be devoted first to a discus-
sion of certain points brought forward in the paper of Sharp
and Millar already referred to, and second to certain practical
considerations arising in arc lamp photometry.
A form of correction for asymmetrical light distribution which
is emphasized by Sharp and Millar is the use of a translucent or
diffusing screen, instead of an opaque screen between the light
source and the test plate. This was originally suggested by
Ulbricht in the case of very small spheres in which it was noted
that with the rotation of a hemispherically asymmetrical light
source, the readings were lowest when the lamp was directed
toward the screen. This is the case with the readings for the
20-inch (50.4cm.) sphere in Fig. 3, the drop being about 2 per
cent. Sharp and Millar quote much higher values of 11 per
7 The practise in this laboratory is to use "factory white" and renew the coating every
two weeks. This is preferable to using an oil paint and attempting to wash the surface,
as a mat diffusing surface is more easily maintained. The relative reflecting power of
white porcelain, white blotting paper, and " factory white," for different wave-lengths of
light was determined with the spectrophotometer. "Factory white" showed a slightly
lower selective absorption in the red end of the spectrum. Otherwise the surfaces were
the same.
CHANCY AND CLARK: ARC LAMP PHOTOMETRY IJ
cent, for an 18-inch (45.7 cm.) sphere and 6 per cent, for a
30-inch (76.2 cm.) sphere. The proposal is to correct for this by-
selecting a screen just translucent enough to transmit the proper
amount of direct light to the test plate and so equalize the read-
ings, for the two positions. This method of compensation is
open to the following objections.
(1) The exact adjustment of screens to particular translucen-
cies is neither simple nor convenient in practise.
(2) The compensation is made by the transmission of direct
light of varying intensity. Since the sole object of the screen is
to prevent such transmission the general integrating capacity of
the sphere is impaired and the adjustment is valid only for the
particular distribution of light flux for which it is made.
(3) Large errors are introduced by slight variations in the
distance of the light source from the screen.
(4) The method is unnecessary. The desired correction can
be made by proper screen position. If the reading is low when
the light is directed toward the screen, as compared with the
reverse position, the relative proportion of the two screened
areas is wrong, and may be remedied by moving the screen nearer
the test plate.
Much more objectionable than the use of an exactly adjusted
translucent screen for a particular type of light distribution has
been the indiscriminate use of translucent screens in certain
commercial integrating spheres placed upon the market, where
there was no pretense of adjustment, and where such use was
ill-advised and harmful. An 80-inch integrating sphere of this
type, with complete photometric equipment was purchased some
time ago from a manufacturer. This sphere was provided with
screens made of translucent diffusing paper. Assuming that the
screens were properly designed, the sphere was placed in service
without special tests. Later a box integrator of the same diam-
eter was built in the laboratory and the arrangement and con-
struction of the screens were copied from the above-mentioned
sphere. As the inner surface of the box integrator was 18
sided instead of spherical, a critical investigation was made of
its integrating capacity as compared with the sphere. It was
found when a series of standardized high power incandescent
l8 TRANSACTIONS I. K. S. — PART I
lamps were successively suspended in the box, in the position
usually occupied by the arc lamp that discrepancies of serious
magnitude frequently occurred. The same experiment was re-
peated in the metal sphere with similar results, the discrepancies
amounting to 4 and 5 per cent.
The experiment with the hemispherical light source was then
tried with the following results in the box integrator. Three
positions were chosen.
TABLE I.
Away
Toward screen from screen
Direction of light flux o° 900 1800
Readings 100 81 74
Since the illumination at the test plate increases 36 per cent.
as the light is rotated around toward the screen from the oppo-
site side, it would appear that the compensation for loss of light
at the test plate was somewhat excessive.
Opaque screens of blotting paper were then employed and the
reading in the three positions differed less than 0.2 per cent. In
the sphere a smaller difference of 18 per cent, existed between
the two opposite sides, due to the fact that the translucent screen
had become somewhat more opaque by reason of age or dust.
But the source of the serious discrepancies with horizontally
symmetrical sources was found to be in the fact that the propor-
tion of transmitted light varied with the distance of the lamp
from the screen. The translucent screen behaves toward the
test plate as a primary light source, and the illumination of the
screen necessarily varies with the distance of the lamp.
TABLE II.— Translucent Screens.
Per cent, change
Distance
lamp to screen
Test plate
illumination
Observed
Calc. inverse
square law
1
r 9 in. (23 cm.)
20.3
O.O
O.O
Clear globe <
11 in. (28 cm.)
18.9
7.0
8.9
1
1 18 in. (46 cm.)
17-3
'4-5
19.0
Diffusing
opal globe .
r 9 in.
11 in.
1 18 in.
.6.3
15.4
13-6
0.0
5-5
16.0
0.0
8-5
19.0
It is seen from Table II that a displacement of 2 inches gives a
change in illumination of about 6 per cent., and a displacement
CHANEY AND CLARK : ARC LAMP PHOTOMETRY 19
of 9 inches a change of about 15 per cent. The change is some-
what less than is calculated from the inverse square law.
In the following table the results with opaque screens are
given which show no change at all for a displacement of 2 inches
(5.08 cm.) and only a slight effect when the distance between
lamp and screen is doubled.
TABLE III.— Opaque Screens.
Distance Test plate Per cent,
lamp to screen illumination change
9 in. (23 cm.) 14.9 O.O
Clear globe- • \ 11 in. (28 cm.) 14.9 0.0
[8 in. (46 cm.) 14.7 1.3
III
9 in. 12.15 0.0
Diffusing opal globe • • -j 11 in. 12.15 0.0
18 in. 12.10 0.4
Inasmuch as the incandescent lamps were merely suspended
in the sphere, variations of over an inch (2.54 cm.) in their
position was easily possible, which accounted for the discrepan-
cies observed when the translucent screens were employed. In
the case of arc lamps exact centering would be impracticable.
Sharp and Millar make a second indictment of opaque screens,
however. They state that —
It has been found that when an opaque screen is used the results are
dependent upon the size of the light source tested. So for example, in
the 80-inch (2.03 m.) sphere the following differences have been found
between results obtained with an opaque screen of the size which it is
desirable to use, and those obtained with the smallest opaque screen which
could be used in connection with the particular light source investigated.
Per cent,
difference
between deter-
minations with
large and small
opaque screens
100 candlepower carbon filament 2.0
32 candlepower carbon filament 3.0
16 candlepower carbon filament 4-°
8 candlepower carbon filament 5-°
4 candlepower carbon filament (sign lamp) 10.0
2 candlepower carbon filament (sign lamp) 10.0
These data indicate that if an opaque screen were used, an arc lamp
with an opal globe would receive an undue advantage in comparison with
the same lamp equipped with a clear glass globe.
20 TRANSACTIONS I. E. S. PART I
They further state that —
Errors due both to the opacity of the screen and to variations in the
relation between its size and that of the light source may be eliminated
by substituting for the opaque screen one of a particular translucency.
The objections which may be raised to the above are two in
number: first, that their experiment does not prove what it is
intended to prove, and second, that if what they desired to show
is true, no conceivable translucency of screens will be of any
avail.
In the experiment quoted the ratio between the large and small
screen becomes successively greater with each succeeding number
of the series. Since the illumination at the test plate depends
directly upon the size of the screen, this adequately accounts for
the increasing divergence with each successive pair of readings.
In the following table are given readings taken successively
with a translucent screen and an opaque screen, first for an
incandescent lamp with clear globe, and second, for the same
lamp incased in a large diffusing arc lamp globe. The results
show that there is the same relative difference, viz., ij per cent.,
between the clear globe and the opal globe whether a translucent
or an opaque screen be used. Or, looked at in another way, the
replacing of the translucent screen with an opaque screen has
cut down the illumination at the test plate by almost exactly the
same amount, viz., 14.4 per cent., whether the area of the light
source was large or small.
TABLE IV.
Translucent Opaque Per cent.
screen screen difference
Clearglobe 24.78 21.19 14.49
Opal globe 20.56 17-59 J4-44
Per cent, difference i7-°7 l1-°° °-°
Sharp and Millar's conclusions, therefore, upon the value of
translucent screens, require revision.
Their original suggestion, however, that the relative areas of
the light sources might affect their relative values as determined
in the sphere was further investigated. As already shown, the
theoretical value of the reflected illumination for an empty sphere
is pi, and the actual value of the reflected illumination read at
the test plate with a screen is [(1 — Bjpld -f Kp'i]. The ratio
CHANCY AND CLARK: ARC LAMP PHOTOMETRY 21
of the reflected illumination with screen, to that without screen
is therefore f(i — 8)a -f- Kp] (10) which for the lack of a better
term we will call the ' screen ratio'.
In the above expression a and p are the absorption and reflec-
tion coefficients of the sphere wall ; K is a coefficient represent-
ing the fraction of the diffuse reflections p2I which escapes ab-
sorption by the screen, and other foreign bodies, and is therefore
nearly unity, and (i — 8) is the distribution coefficient repre-
senting the fraction of the total light flux falling upon the un-
screened area or central zone of the sphere. There is nothing in
this expression dependent upon the area of the light source.
Unless the area of the source changes the distribution of the flux
it should be without influence.8
The use of diffusing globes upon asymmetrical sources does
change the resulting distribution curves giving in general a
more symmetrical distribution. This means that the ratio
[(i — 8)a + Kp] for a clear globe may be either greater or less
than the corresponding ratio for the same source with a diffusing
globe.
If the clear globe has a relatively large fraction, 8, of the
total light flux falling upon the screened areas, a diffusing
globe may diminish this and increase the value of the ratio
[(i — B)a + Kp]. That is, the diffusing globe will have a rela-
tive advantage.
If on the other hand the fraction of the light flux, 8, falling
upon the screened areas is much below the average, a diffusing
globe may increase 8, and diminish the ratio given by the ex-
pression [(i — 8)a -f Kp]. That is, the diffusing globe will
have a relative disadvantage.
A direct experimental method of measuring the 'screen ratio'
8 The proof that a large light source will undergo the same screen absorption as a
small source of equal candlepower is simple when the distribution is assumed uniform
for both cases.
Imagine equal spheres described about the center of both light sources, then since
both sources emit the same total flux uniformly distributed, equal portions of the surface
on the two spheres are traversed by equal light fluxes. If the radius of the imaginary
sphere is so taken that the edges of the circular screen lie on the sphere surface it is clear
that the screen marks off a definite portion of the sphere surface and therefore receives
the same light flux from either the small or the large light source above assumed. This
is the necessary and sufficient condition for equal absorbing effects on both light fluxes.
It is true that the light distribution on the portion of the integrating sphere around
the screen shadow is different in the two cases, but this difference has no effect on the
illumination at the test plate if the portion of the sphere surface involved has a uniform
reflecting surface.
22 TRANSACTIONS J. K. S. — PART 1
[(i — 8)<x -j- Kp] for any given screen and light source was de
vised as follows :
Measurements are made of the illumination at the test plate
under three conditions.
Let A — direct light flux only.
B = direct plus reflected light flux (without screen).
C = reflected light only (with screen).
A, the actual direct illumination upon the test plate from the
unscreened light source, is measured by attaching the lamp in its
proper position to the half of the sphere containing the test
plate. The opposite half is removed and a series of black screens
are set up between the test plate and the lamp to cut off all light
except that directly from the source.
B is measured with the sphere closed, in the usual manner,
but with no screen. B — A is therefore equal to the theoretical
value of the reflected illumination, pi, for an empty sphere (ex-
cept in so far as the lamp and its supports may act as a screen).
C is the value of the reflected illumination as usually measured
with screen and is equal to (i — S)pl</ -\- p*I.
Therefore C/(B — A) = [(i — B)a + Kp] the "screen ratio."
Table V gives a series of measurements made in this manner
with a light source having a clear globe, and with the same light
source after being incased in an opal globe.
TABLE V.
ABC C/(B — A )
Clear globe 8.69 36.64 26.38 0.944
Opal globe 5.8 28.35 21.61 0.958
It is seen that under the particular conditions of this experi-
ment the opal globe has a slight relative advantage over the clear
globe. The results are not open to complete explanation since
the relative differences in distribution are only partially indi-
cated by the values of the direct illumination A, at the test plate,
as the average intensity of the light flux upon the rest of the
screened areas is unknown, and may not be proportional to A.
The method as outlined, however, affords a very direct and
simple means of investigating special characteristics of the
spherical integrator and further data would be of interest.
CHANEY AND CLARK: ARC LAMP PHOTOMETRY 23
Another source of error in practical arc lamp photometry which
is carefully avoided in German practise has apparently received
no attention from the designers of American built spheres. The
error consists in a faulty method of determining the "sphere
constant."
In the substitution method employed with the sphere the ratio
between the known flux of a standard lamp, as separately deter-
mined, and its illumination as photometered at the test plate gives
the "sphere constant," by which any other illumination as read
at the test plate may be converted to terms of the flux or mean
spherical candlepower of its source.
This constant9 must contain in itself all of the factors affecting
the relations between light flux and test plate illumination, such
as size and surface of sphere, ratio of screened and unscreened
areas, absorption of reflected light by foreign bodies such as arc
lamp mechanism, screens, etc.
Not only do large lamp mechanisms absorb reflected light, but
they screen certain parts of the sphere wall from the test plate,
thus changing the ratio of screened and unscreened area.
Therefore, the standard lamp must be read with the arc lamp
in position, in order that the sphere constant may contain the
proper corrections. But since only reflected light can reach the
arc lamp supports when the latter is burning, the same condition
must be observed with the standard lamp. That is, none of the
direct rays of the latter must strike the arc lamp. The German
practise is to place the standard lamp below the arc lamp with a
small cap upon the former to shield the arc lamp. The standard
lamp must be standardized with this cap in place. In the above-
mentioned sphere, however, the standard lamp is placed laterally,
where the most intense part of the flux will fall upon the arc
lamp parts, and no screen or shield is provided. The arc lamp
therefore absorbs a considerable amount of direct light in addi-
Flux standard lamp _
' Sphere constant = 1]Ulmination standard lamp as read at test plate
4irR2qI 4"-R*ag
(I - S')plrf + Kp2I ~ «[(l — «') + Kop]
If R = radius of sphere.
a. = absorption coefficient,
p = reflection coefficient.
(1 — 8') = fraction of direct light falling on central zone of sphere.
(1 — K) = fraction of reflected light absorbed by screens and foreign bodies of all kinds.
24 TRANSACTIONS I. E. S. — PART I
tion to the usual amount of reflected light. This increases the
sphere constant and the resulting values for the arc lamp are
high. An arc lamp which intercepts and absorbs a large propor-
tion of direct light is thus favored over a lamp with smaller or
more highly reflecting mechanism.
In this laboratory where many types of arc lamps are employed
in the testing of experimental and factory carbons, the correction
for the change in sphere constant caused by introducing the arc
lamp into the sphere is determined by placing a small screen
upon the standard lamp of sufficient size to screen the arc lamp.
The standard is read with the sphere empty and then with the
arc lamp in position. A factor is thus obtained for the influence
of this particular arc lamp upon the sphere constant. The cap is
then removed from the standard lamp, and the constant for the
empty sphere with known light flux determined. This constant
multiplied by the lamp factor previously obtained, gives the cor-
rection for the lamp in question.
This method has the great advantage that once the specific
factor for each lamp has been determined it is only necessary to
determine the constant of the empty sphere thereafter. The
latter need be determined but once a day, no matter how many
different lamps are being photometered.
Where the primary object is the comparison of different car-
bons in the lamps, it becomes necessary to determine the trans-
mission and absorption factors of the globes so that the data
over long periods of time may be independent of the particular
globes in use. Fairly uniform opal globes are selected and stand-
ardized separately by incandescent lamps, and the globe factor,
together with the corresponding lamp factor, is applied to the
particular value of the sphere constant as determined for the
day upon which the test is made. By placing an incandescent
lamp inside the arc lamp with globe complete, a combined lamp
and globe factor may be determined. Since the incandescent
lamp has neither the exact position or distribution of the bare
arc, the resulting candlepower values are not those of the naked
arc, but are proportional to them, and are independent of chang-
ing globes.
If the actual illumination of the arc lamp is desired, then the
CHANEY AND CLARK: ARC LAMP PHOTOMETRY 2$
latter method is inapplicable, and no globe factors should be
employed.
A brief consideration will now be given to a source of error in
the practical photometry of arc lamps which has apparently been
too frequently neglected.
All commercial products are subject to characteristic varia-
tions and lack of uniformity, the range and extent of which
depends upon the type of product, the inherent difficulties of
manufacture, and the standard of quality maintained by the
manufacturer. No trustworthy comparison of similar types of
competing illuminants is possible without a knowledge of the
characteristic range of variation of the particular products under
test. The measure of the uniformity of a product is not only
essential in determining the true arithmetical value of the prop-
erty being measured, but also in determining the commercial
worth of such value when found. Moreover, the testing labora-
tory requires a knowledge of the precision measure, or average
deviation of the individual samples from their general mean, in
order to obtain the most economical and efficient distribution of
the time and labor spent upon the test. For example, let it be
assumed that the actual variation in physical and illuminating
properties of a certain class of carbons is 5 per cent. That is,
any single trim will show upon the average a difference of 5 per
cent, from the mean value of a large number of such trims. It
is then obvious that no matter how exhaustively a single trim
may be tested, the result will still differ on the average by at
least 5 per cent, from the normal value, and may quite possibly
differ by three times the average deviation or 15 per cent. The
only possible way by which a closer approximation to the general
average value can be secured is not by increasing the accuracy
or number of measurements upon a single trim, but by increas-
ing the number of the trims tested. The average deviation of
the mean of several independent trims decreases in proportion to
the square root of their number. That is, four trims are required
to reduce the average deviation one half.
If the actual physical differences possess an average deviation
of 5 per cent., the average deviation of the values as measured
26 TRANSACTIONS I. E. S. — PART I
will be still greater, because superposed upon the variations due
to the actual differences of the carbons from one another, will
be the variations due to errors of measurement upon the indi-
vidual carbons. Assume that the latter has an average deviation
of i per cent. One has, then, a i per cent, average deviation due
to errors of measurement superposed upon a 5 per cent, average
deviation due to variations in the product measured.
The resultant deviation is not, however, the sum of these two,
/. e., 6 per cent., but is the square root of the sum of their squares,
i. e., 5.1 per cent. Thus if the two variations are represented as
the sides of a right angled triangle, the resultant deviation is
equal to its hypotenuse. From this it follows that if one devia-
tion is very small with respect to the other, relatively large
changes in its value will have a relatively slight effect upon the
resultant deviation. Thus in the example above the errors of
measurement may be increased so that their average deviation
of 1 per cent, is increased to 2 per cent, and the resultant devia-
tion will only be increased from 5.1 per cent, to 5.38 per cent.
Whether the average deviation in measurement of a single trim
should be 1 per cent, or 2 per cent, depends upon the relative
number of samples which can be tested in each case with the
same total cost in labor, materials and overhead expenditure.
If it costs no more in a given case to secure an average deviation
of measurement of 1 per cent, than of 2 per cent., then the
smaller value should be secured, however slight its effect upon
the final result may be. Suppose, however, that the time of
testing and the number of observations can be cut in half (i. e.,
from 1 -hour to J^-hour) with an increase in the average devia-
tion of measurement from 1 per cent, to 2 per cent. Then if
two J/2-hour trims can be tested with the same cost as i-hour
trim, the average deviation for the latter is 5.10 per cent, and of
the former is 5.38/1/2" per cent. = 3.8 per cent, for the same
unit of cost.
The significance of this is more clearly seen by the statement
that 26 1 -hour trims or 29 J/-hour trims will be required to
secure an average deviation of 1 per cent, for the final result,
which means a saving of 44 per cent, in the cost of testing to
secure the same degree of accuracy in the final result.
CHANKY AND CLARK: ARC LAMP PHOTOMETRY TJ
The criterion for maximum efficiency of testing in all cases is
that the ratio of the resultant average deviation for a single
sample, from all causes whatsoever, to the square root of the
number of samples which it is possible to test with any given
unit of cost, shall be a minimum.
In practise, the evaluation of the various independent sources
of variation is somewhat more complicated than is shown by
the hypothetical example above quoted and the particular details
must be worked out for the special conditions of each laboratory.
However, it serves to illustrate the principles employed in this
laboratory in determining the length of tests upon single trims,
the number of photometric reading's, and the number of duplicate
trims. Enough has been said to indicate that in the practical
photometry of arc lamps something in addition to the errors of
the photometric apparatus must be considered, and that it is
quite possible to make very accurate photometric measure-
ments and yet obtain very inaccurate data unless due regard is
had for the relative magnitude of the errors of measurement
and the variation in the thing measured.
Acknowledgement is hereby made to Mr. R. B. Chillas, Jr., for
kindly assisting in the preparation of the manuscript.
DISCUSSION.
Dr. C. H. Sharp: Since the authors of the paper have been
kind enough to rake out of oblivion the paper which Mr. Millar
and I prepared on this subject, I think I may, with propriety, be
permitted to discuss their present paper. Our paper back in 1908
was prepared with a certain end in view ; it was to put before the
members of this Society what at that time, in this country, was a
practically unknown photometric device which we believed to be
of very great value. This paper says that it was unfortunate that
we did not deal more fully with the theoretical aspects of the
subject. We had. however, the idea that the value of our paper
to the members of this Society would not be in direct ratio to the
amount of mathematics that we could put into it, consequently
we did not involve our discussion in any nebulous haze of
Teutonic theory (laughter) ; but tried to get down to the engin-
eering facts of the case as we knew them. Well, a good deal of
28 TRANSACTIONS I. E. S. — PART I
water has run under the bridge since 1908, and if our opinions
in all respects at the present time do not agree with what we held
at that time, I am willing to let it go that we perhaps have prog-
ressed and know more now than we did then. As to the facts and
data presented at that time, I have no apologies to offer, as I
know they were correct and all right as far as they went. I think
it is most timely and fortunate that the authors have taken up
more fully at this time the theoretical consideration of the in-
tegrating sphere and of the errors which may enter into its use.
Any considerable discussion of these points at that time might
perhaps have been out of place. At the present time such a dis-
cussion is needed and I think that we are fortunate to have so
lucid and able a one as the authors have presented to-day.
I am impressed more and more with the possibility of the use
and misuse of the integrating sphere. In view of the possibility
of misuse, for instance, of the translucent screen as shown by the
authors and as borne out to some extent in our own experience,
I have been for some time inclined to the view that on the whole
the opaque screen was the best thing to use, certainly in a large
sphere. I think that the paper shows in a very remarkable way
the precision with which the sphere will integrate the total flux of
light from almost any source whatever when it is used in any
ordinarily reasonable manner; and as a guide to the proper use
of the sphere, the theory presented is most timely and valuable.
Mr. W. F. Little : A number of experiments have been made
at the Electrical Testing Laboratories to determine the accuracy
as well as the flexibility of the integrating sphere with translucent
screens.
TEST NO. 1.— Translucent Screen.
Lamp Extensive Intensive Focusing
alone reflector reflector reflector
Position in sphere per cent. per cent. per cent. per cent.
1 ft. from top 100.0 IOO IOO 100
2 ft. from top 100.0 100 100 —
3 ft. from top 99.5 100 — 100
Test No. 1 referred to above consisted of mean spherical can-
dlepower readings of a tungsten lamp, alone and when equipped
with intensive, extensive and focusing prismatic reflectors
mounted in various positions in the sphere.
ARC LAMP PHOTOMETRY 29
Test No. 2. — A porcelain enamelled parabolic reflector having
an asymmetrical distribution was measured in two positions,
pointing toward the screen and at 90 deg. to the screen.
TEST NO 2.— Porcelain Enamel Double Parabolic Reflector.
Translucent Opaque
per cent. per cent.
Toward screen 103 90
900 to screen 100 100
Test No. 3. — A bare lamp with one side covered with black
paper oriented in several positions.
TEST NO. 3.— Lamp with Black Paper on one Side.
Translucent Opaque
per cent. per cent.
Toward screen 100 104
900 to screen 100 100
1800 to screen — 100
Even under the above abnormal and adverse test conditions,
the above figures show comparatively small photometric errors,
and the results are somewhat more consistent with the translucent
screen. However, under normal working conditions it is known
that the errors introduced by either screen are negligible.
The authors of this paper have stated that the only absorption
of light by the lamp or accessory to be corrected for is the ab-
sorption of reflected light; no direct light from the standard
lamp should fall upon the lamp or accessory. First, the amount
of direct light from the standard falling on the lamp or accessory
in the 80-inch sphere as used at the Electrical Testing Labora-
tories is very small and almost negligible. Second, it is the prac-
tise at the Electrical Testing Laboratories to cover the lamp hous-
ing with a white diffusing substance so as to reduce the absorp-
tion to a minimum, or so to mount the lamp that the housing and
opaque portions are outside of the sphere; therefore, this crit-
icism can be easily taken care of.
The Laboratories also find a small 40-inch integrating sphere a
very valuable and convenient adjunct to the testing of arc lamps.
It has been successfully used by lowering the lamp in from the
top and placing an opaque screen horizontally in the center of the
sphere with a mirror set at 45 deg. to the vertical placed im-
mediately beneath it. The elbow tube of a portable photometer
is placed in a small hole in the side of the sphere, so located that
3
30 TRANSACTIONS I. E. S. — PART I
the photometer tube then points at the mirror, which reflects the
surface of the sphere immediately beneath the screen, thus using
the surface of the sphere rather than the translucent test plate
for its comparison surface. A small comparison lamp is placed
on top of the screen tip upward. This is used to measure the ab-
sorption of light by that portion of the arc lamp which is allowed
to remain in the sphere at the time of measurement. Here again
the amount of direct light falling upon the arc lamp is very small,
as the tip candlepower of the comparison lamp is relatively low.
Also the opaque screen is advantageously located for the arc
lamp, as the end-on candlepower of the arc is comparatively low.
The integrating sphere has been used very advantageously in
the measurement of light loss with various accessories to in-
candescent lamps. A sufficient number of tests have been made
by the "point by point method" on several photometers and
spheres to prove the accuracy of the sphere method in securing
this value. Lamps of very different reduction factors, and even
metal and mirror reflectors, have been measured with very close
agreement between the sphere and distribution determinations.
In all of this work the Laboratories have used opaque screens
merely because they are more convenient ; however, it is probable
that when used with discretion a slightly higher degree of ac-
curacy is obtainable with translucent screens.
Mr. S. L. E. Rose : This paper is of a great deal of interest
to photometrists, and one of the points which I wish to emphasize
in the paper which was not brought out in the reading, is the
method of test; that is, it is better to test a number of elec-
trodes and take fewer readings on each one than to take a lot
of readings on one electrode, if you want an average of what that
particular light source will do. That has been the practise at the
laboratory which I represent, for some time, as was brought out
in the paper1 at the Chicago Convention of the I. E. S. by Mr.
Stickney and myself.
I don't see any mention in the paper of what was used for
painting the inner surface of this sphere. I am interested in
that and would like to know if the authors made any investiga-
tions as to the best paint or material to use for that purpose?
1 Stickney, G. H., and Rose, S. L. E., Photometry of Large Light Sources; Trans.
I. E. S., vol. VI, p. 641.
ARC LAMP PHOTOMETRY 3 1
While it is a little out of the range of this paper, it will prob-
ably be interesting to give you one special application that we
made of our sphere at the laboratory in connection with some
work for the Panama-Pacific International Exposition. It was
necessary to know how the light was dispersed from the jewels
which are to be used in connection with the illumination of the
buildings of the exposition; a number of different makes were
submitted with different cuttings and we wanted to know which
was the best for the purpose. It would have been an almost
endless job to have found out the number of reflections which the
jewels gave back from the front faces without the use of our
sphere. We simply took one half of the sphere, mounted the jewel
at the center on the axis and projected a beam of light through
the photometric window, and by means of a small mirror reflected
it on to the jewel normally and then made a photograph of that
half of the sphere, and we had immediately the distribution of
reflected spectra from that jewel; and then we could simply
introduce the different jewels which were submitted to us, take
a photograph and count the number and see which one was
giving the most reflections and the clearest and most intense
spectra. By means of radial and circular lines drawn on the
photographic print, we could locate them, i. e., we had longitude
and latitude and could tell exactly where they were. This work
was very convenient, very simple and done in the minimum of
time. Fig. A is print from negative of a good jewel and Fig.
B is print from negative of a poor one. The circular lines are
drawn at intervals of 10 deg.
I am about in the same position as Mr. Little ; our sphere is
not in constant use, in this way — it might be used for a week
steadily and then perhaps stand idle a week, and in that case it
gets a coat of dust and we find it is awfully hard to brush that
dust off. We use white alabastine and when you go to brush
that, it will mix up with the dust and the best way out is simply
to paint it over. If we are using it right along, it is probably
painted every week; but we might paint it and use it three or
four days and then it might set for a month. I might say, though,
that practically it is painted every time it is used. I don't want
you to understand from that that we paint it every day.
32 TRANSACTIONS I. E- S. — PART I
The Chairman : Take a piece of new, white, fresh blotting
paper, etc.
Mr. S. L. E. Rose: Well, it is not entirely a matter of dis-
coloration, it is more a question of collection of dust and our
sphere happens to be in a particularly dusty place, and for that
reason we have to paint it oftener than would otherwise be
necessary. We use white blotting paper for the internal screens.
It seems to me there is a chance for the Committee on Nomen-
clature to define the different branches of photometry. We hear
of precision photometry; this morning we had a paper which
spoke of practical photometry, and we have another branch that
is called commercial photometry, and the degree of accuracy
necessary for one may be entirely out of the question for the
others. Mr. E. J. Edwards of Cleveland a short time ago in an
article in the engineering department news discussed practical
accuracy and wasteful accuracy, — there's the two kinds. Prac-
tical accuracy is all we are after in commercial photometry, and
the degree of accuracy necessary for precision work would be
wasteful in this case.
The Chairman : Dr. Middlekauff, what do you use at the
Bureau of Standards?
Dr. G. W. Middlekauff: White alabastine. However, our
experience with the sphere has been limited, having been confined
almost entirely to the acceptance tests. Although a test of the
color absorption by the coating then in the sphere was made
incidentally, we were, at the time, more particularly concerned as
to the accuracy with which the instrument would reproduce
relative values as found by other methods when light sources of
the same color were compared. The best results were obtained
with an opaque screen reduced in size as much as possible.
The Chairman : Would that vary for each size of lamp?
Dr. G. W. Middlekauff: For our carbon standards, which
consist of several groups, each group having a different type of
filament, but all having the same size of bulb, accurate relative
values were obtained. But for lamps of different sizes of bulb,
the area of the screen remaining the same, the agreement in rela-
tive values with other methods was not so good.
Fig. A— Photograph of reflections from a t:ood jewel.
Fig. B.— Photograph of reflections from a poor jewel.
ARC LAMP PHOTOMETRY 33
The Chairman : What is the size of your sphere?
Dr. G. W. MiddlEkauff : Thirty inches in diameter. This
was considered large enough for our purpose of comparing in-
candescent lamps.
In the color absorption test referred to, we used two carbon
lamps that matched in color at about no volts. When one of
these lamps was placed inside the sphere, from which the translu-
cent window had been removed, the other lamp had to be reduced
about 10 per cent, in voltage to bring them again to a color match.
There being so great a change in color due to selective absorption,
it would not be surprising, when lights differing considerably in
color (as for example a 4-watt carbon and a ^4-watt tungsten)
are compared in the sphere, if we should find their relative values
quite different from what they would be if the comparison were
made outside the sphere by some other method.
In preparing a later coating, it was found by a little experi-
menting that a very small quantity of Prussian blue mixed with
the white alabastine before applying to the sphere reduced
selective absorption considerably. With this coating, it is believed
the sphere will give quite accurate results in the comparison of
differently colored lights.
This simple color test is mentioned in order to emphasize the
fact that if the sphere is to be of value in accurate standardiz-
ing work in which lamps having widely different colors are to
be compared, the character of the coating is equal in importance
to the proper design of the instrument.
The Chairman: Mr. Cady do you have a sphere?
Mr. F. E. Cady : No, we have no sphere. At the Bureau of
Standards, when the sphere first appeared, we were very much
interested in integrating photometry, but we were in possession
of a Matthews type which had proved very satisfactory, and
consequently, the sphere did not receive the attention which it
would otherwise have had. The engineering department of the
organization I am connected with, however, has an integrating
sphere of the 30-inch type, I believe. What little experience we
have had in attempting to determine the candlepower per incan-
descent lamp of that sphere has been similar to that of Dr. Mid-
34 TRANSACTIONS I. E. S. — PART I
dlekauff ; that is, once or twice we have attempted to determine
spherical candlepower of lamps with filament windings, different
from those of a standard whose mean spherical candlepower we
knew, and the results seemed to have some discrepancy. The
lamps were afterwards measured on a universal photometer and
the mean spherical candlepower calibrated, and we found differ-
ences amounting to 2 or 3 per cent. The cause for those discrep-
ancies we did not have time to investigate, but I should like to
know whether the authors of this paper, who seem to have con-
fined their work more to arc lamp photometry, have done much in
the work with the incandescent lamp and whether they have found
that with suitably designed screens, it is possible to take, for
instance, an ordinary carbon lamp as a standard, and with that
determine the mean spherical candlepower accurately of a lamp
having a distribution such, for instance, as that of the old carbon
downward light lamp, or in the modern tungsten lamp, those
which have filament windings of the spread umbrella type.
Mr. R. B. Chillas, Jr. : There are a few points which may
be of interest in connection with equations 2 and 4. In the latter,
it is seen that the direct light is equal to the light absorbed, and
so disappears as heat radiated from the external sphere walls.
Equation 2, the total illumination is equal to the direct light
divided by the absorption coefficient, affords a means for ob-
taining a quantitative value of light wall coverings. The follow-
ing table gives the ratio of total illumination to that obtained
from the source with different reflection coefficients.
Reflection
coefficient
total
Ratio
illumination
P = 0.80
5-00
0.60
2.50
0.50
2.00
O.4O
1.66
0.20
1.25
The calculations for minimum screened area were based on
obtaining a trigonometric expression for the heights (propor-
tional to the areas) of the two shaded zones, substituting in this
the values of the trigonometric functions expressed in terms of
ARC LAMP PHOTOMETRY 35
sphere radius, and fractions of sphere radius, differentiating,
and equating the first derivative to zero.
The resulting expression is quite complicated and is best solved
by successive approximations.
Dr. C. H. Sharp: Regarding the interesting suggestion of
using a screen with a mirrored surface toward the lamp, I think
the trouble is that it is pretty hard to get a very much higher
coefficient of reflection from a mirrored surface than it is from
a good, white diffusing surface. It takes a pretty good piece of
mirror glass to reflect 80 per cent, of the light and a good white
diffusing surface will do as well.
Mr. C. W. Jordan : In the practical working of an integrat-
ing sphere it is assumed that the operator has carefully tested the
apparatus to eliminate any systematic errors. For example.,
errors of serious magnitude due to the use of an improperly
placed translucent screen can easily be detected by photometering
the standard lamp placed in the test lamp holder, after checking
in its normal position.
In my opinion the general practise has been to check integrat-
ing spheres in this manner and the photometric readings of the
standard made to agree when in either position by proper ad-
justment of the position or translucency of the screen.
One of the sources of error when using the sphere has been
due to the relatively greater collection of dust in the lower hem-
isphere than in the upper. When the light distribution of the
lamp being tested differs materially from that of the standard,
this error may become serious. Constant repainting becomes
necessary to eliminate this error.
I wish to ask what type of photometer was used in making the
photometric measurements and the order of its sensibility com-
pared with the sphere errors found.
I think the authors are to be congratulated for their excellent
work of individually analyzing the sources of error in the use of
a sphere and for the recommendations for their elimination.
Dr. N. K. Chancy (In reply): In replying to Dr. Sharp's
very kind comments upon the paper we may frankly say that
Dr. Sharp's general position with respect to the intent of his
earlier paper is perfectly sound and beyond criticism. We still
36 TRANSACTIONS I. K. S. — PART I
venture to believe, however, that it has proved somewhat unfor-
tunate for the development of the use of the sphere in this
country, that Dr. Sharp's valuable introductory paper was not
more promptly supplemented by further theoretical treatment,
in which the then existing "haze of Teutonic theory" would
have been made more accessible, and perhaps more intelligible to
American workers. The present treatment is based upon a more
unified physical conception of the sphere, and we trust will prove
less "nebulous" than its Teutonic predecessors.
Where issue was taken with the earlier paper, the case must
rest upon the merits of the respective arguments.
Mr. Little, however, has presented certain tables for the ap-
parent purpose of showing that translucent screens are as good
or better than opaque screens. So they are, if particularly ad-
justed for particular cases. The point made in the paper was
that this particular adjustment was not only difficult in practise,
but was made at the expense of general integrating power for
all-around work. That Mr. Little is not seriously impressed
with the showing made by his own figures is clear from his
frank admission that they employ opaque screens in all of their
work, "merely because they are more convenient." The reasons
for the "inconvenience" of translucent screens are thoroughly
discussed in the body of the paper.
The "slightly higher degree of accuracy" obtainable by trans-
lucent screens, is we believe purely mythical, provided the same
amount of "discretion" is used with opaque screens and the
proper corrections are made. Where the lamp supports are small
or are not introduced into the sphere Mr. Little is correct in
assuming that the correction for direct flux from the standard
lamp falling upon the lamp supports is negligible. Where the
whole arc lamp is introduced into the sphere, as is the practise
in the laboratories of the National Carbon Co., the correction
for direct flux absorbed in lamps in some cases may amount to
as high as 8 per cent, of the reading. In our experience it is
simpler to make this correction once for all with each arc lamp
used, and then take all regular standard lamp readings with the
sphere entirely empty, to correct for daily changes in the walls of
the sphere.
ARC LAMP PHOTOMETRY 37
Dr. Middlekauft' and Mr. Cady, both raised questions concern-
ing the amount of discrepancy likely to occur between different
types of incandescent lamps with various filament windings. If
the size of sphere and screen, and the approximate distribution
curves of the lamps are known this error could be figured out
directly by means of a sphere diagram and the formulae in the
paper.
In a sphere of reasonable dimensions with proper screens, the
variations from this cause should be very small — less than i
per cent. If the sources are very unsymmetrical it is always
important to direct the most intense parts of the flux upon the
central unscreened area of the sphere, if the lowest limits of
error are to be obtained.
In reply to Mr. Jordan's questions,— a Sharp-Millar photom-
eter was employed. With our standard incandescent lamps upon
a line voltage hand-regulated by a rheostat, the average deviation
of the mean of 20 readings is slightly less than 0.25 per cent.
The data in the paper was the average of two or more independ-
ent readers in all cases.
In adjusting screens the test lamp screen should be set up
according to the proper formula, and then the standard lamp
screen may be adjusted by reading the standard lamp in both
positions as Mr. Jordan suggests. It would be possible, however,
to have both screens wrong and yet secure identical readings with
the same lamp. The real test is the agreement in the two posi-
tions of lamps of different distribution.
In regard to painting the sphere, attention is called to the
foot note upon the sixteenth page of the paper.
The matter of precision in commercial work, — obviously that
is to be decided by the needs of the work in hand. It is always
proper to find what degree of precision is possible upon any
instrument, and then decide how much of that precision is re-
quired for any particular purpose.
3^ TRANSACTIONS I. E. S. — PART I
NEW DEVELOPMENTS IN THE PROJECTION OF
LIGHT.*
BY E. C. PORTER.
Synopsis: This paper deals with the theory of the projection of light.
It shows different methods of concentrating light into a beam and men-
tions the different factors which must be taken into consideration in the
design of lenses, reflectors and light sources for light projection. The
theory is followed by a short description of the practical application of
the new focus type tungsten lamps to headlight service, signal work, navi-
gation, stereopticon lanterns and advertising lighting.
The concentration of light into beams for projection purposes
has been a field of experiment for many years. Probably one of
the best known early applications of light projected to a dis-
tance, and one which to-day is playing an enormous part in the
struggle for supremacy raging in Europe, is that of the naval
searchlight. Here the light generated by a powerful arc lamp has
been used largely for defence, i. e., to show up attacking torpedo
boats before they can get within striking distance and discharge
their deadly "whitehead."
Another old and familiar application is in stereopticon work,
largely for illustrating lectures, etc. Headlight service is another
common use, the light being projected to a distance for a double
purpose : ( i ) to act as a warning of the approach of a train to
trespassers, yardmen, etc., (2) to illuminate obstructions on the
right of way, or whistle posts, etc. Until recently the oil lamp was
the most widely used equipment for this class of service.
That these applications of projected light were rather limited
was due largely to two reasons. Powerful searchlights, such as
arc and calcium, were expensive, complicated and required ex-
pert attention ; while the oil lamp was not powerful enough for
various other applications.
When the incandescent lamp was developed it was realized by
Mr. G. H. Stickney that here was a possible light source for
* A paper read at a meeting of the New England Section of the Illuminating Engi-
neering Society, November 10, 1914.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
PORTER : PROJECTION OF LIGHT
39
various other forms of projectors; not so powerful, simpler and
more economical than the arc, and yet of greater capacity than
the oil light. Under Mr. Stickney's direction, a thorough study
of this field is being carried on at the Edison Lamp Works of
the General Electric Company.
Before taking up the applications of incandescent lamps in
particular, to projection work, I will review briefly some of the
fundamental principles pertaining thereto. Assume, for ex-
ample, that each ray of light emanating from a light source is
of ioo candlepower intensity. If one of these ioo candlepower
r
h
C
d
z
f
*
U"
**
f<>
<
i
4
/
/
t
<?,
£
f
£
i
Si
X.
r
6
c
4
r.
f
Fig- i. —Diagram showing construction of the parabola.
rays be redirected so as to coincide with another, the result is
200 candlepower in the latter direction. Similarly, adding
together many rays from a low candlepower source, produces a
beam of many times the intensity of the original light.
There are two general methods of accomplishing this : one is
by refracting the light rays with transparent lenses; the other
by reflecting the rays with opaque reflectors. In each case, to
obtain the best results, the light must all originate as nearly as
possible from one point. The smaller this point, the more pow-
erful will be the beam obtained. All light rays which fall on a
40 TRANSACTIONS I. E. S. — PART I
convex glass lens will be bent or refracted as they enter the
glass. They will be turned again as they leave the lens, those
originating at the principal focus finally emerging in parallel
rays. Rays of light originating at the focus of a parabolic re-
flector1 will be reflected in parallel lines. Thus, either apparatus
produces the beam of the so-called "searchlight." Fig. 2
illustrates this, showing the cross section of a convex lens and a
parabolic reflector, indicating the paths of the light rays.
As already mentioned, the smaller the dimensions of the actual
light source, the more powerful and narrower will be the beam
obtained. In other words, the greater the departure of the light
source from a theoretical point, the more will the rays be scat-
tered. Consider, for example, a spherical light source, having its
lens ffe-f/ec/or
Fig. 2.- -Diagram showing projection of light rays from a point source by a
convex lens and a parabolic reflector.
center at the focus of a convex lens, Fig. 3. A light ray a orig-
inating at the focal point of the lens will be turned parallel to the
axis; a ray b, originating at the surface of the sphere will be
similarly bent in passing through the lens. This will bring it
below the horizontal; in other words scatter it. The further
away from the focus the light originates, the greater will be the
divergence. Thus, it becomes evident that the smaller the light
1 A parabolic reflector is a highly polished surface so formed that all light rays
emanating from a certain point called its focus, will be reflected in parallel lines. Such
a surface is formed by rotating a parabola aiound a horizontal axis through its focus,
thus forming a surface of revolution.
A parabola is the path of a point moving in such a manner as to be always equidistant
from a fixed point (called the focus) and a fixed straight line (called the directrix)— see
Fig. 1. The mathematical formula is Y! = 4px, where Y = half of diameter; jjt = depth;
p = focal length of the parabola. To construct a parabola, take a piece of cross section
paper; assume a directrix YY; assume a focal length gfand let, ag = gj. To find where
the parabola cuts bb, take a compass and using ag as a radius and/as the centre, strike
an arc till it cuts bb at the pointy, which will be on the parabola. Similarly, using a/as
a radius and/as a centre, another point h on the parabola may be obtained, etc.
PORTER : PROJECTION OF EIGHT
41
source, the more nearly parallel will be the rays ; hence the more
powerful the resultant beam. The same thing holds true for
parabolic reflectors.
It is not practical to produce an absolute point source of light ;
hence, beams from even the most highly concentrated light
Fig. 3.— Diagram showing projection of light rays from a spherical
source by a convex lens.
I • £/y/rf Jovrce
f'foCt/3 Of A*
1-3-C- £/£/>/■ Cones
Fig. 4.— Illustrating cones of light from spherical light source in parabolic reflector.
sources — such as the crater of a small arc — will have a spread, de-
pending in amount and direction upon the size of the source and
the focal length of the lens or reflector. For example: assuming
that we have a spherical light source, the projected beam will be
42
TRANSACTIONS I. E. S. — PART I
round and have a maximum spread limited in the distance by-
two rays a and b shown (Fig. 4) striking the center of the re-
flector and tangent to the sphere. The spread from all other
points of the lens or reflector will be decreasing towards its edge.
Each point of the reflector will receive a set of extreme tangent
rays; hence each point emits a little cone of light. The sum of
all these cones make up the whole beam, which, therefore,
actually consists, up to a certain point, of converging and diverg-
Fig. 5. — Diagram illustrating actual beam from searchlight.
Parcr6o//c ffef/ecfor farabo/tc ftef/ecfor of /"focus
of /" focus
L - L/fftt Source
f' foe a/ fo/nt
Fig. 6. —Diagram showing maximum spread of beam from large and small light sources
in the same focal length parabolic reflector.
ing rays, which at some distance cross and all become diverging
— as shown in Fig. 5. In the same reflector the maximum spread
from a large light source will, therefore, be greater than from a
small light source, each being located at the focus, Fig. 6. If the
same size light source is used in a long focus lens or reflector, the
spread will be less than in one of short focus (Fig. 7). The
shape of the resultant beam depends upon the shape of the light
source. For example, an incandescent lamp having its filament
porter: projection of eight
43
in the form of a helix with its major axis greater than its
diameter would throw an. elliptical beam, because the spread
along its axis would be greater than across its diameter.
To demonstrate the enormous effect of the size of the light
source upon the intensity of the resultant beam, I had five lamps
made, all of the same candlepower (32) but of varying filament
concentrations (Fig. 18). Each of these lamps was focused in
a parabolic reflector 11 inches (27.9 cm.) in diameter and of
Pam6o//c flef/ecfi>r
of /" focus
/'aro6o//c /fef/ectoy
of S" focus
/"• foca/ Po/n+
/. ' L if /it Source
Fig. 7. — Diagram showing maximum spread of beam from same light source in short
and long focus parabolic reflectors.
5-in. (12.7 cm.) focal length. The maximum beam candlepower
measurements were as follows :
Lamp Beam cp.
32 candlepower 240 volt carbon, regular 268
32 candlepower 240 volt carbon, stereopticon 555
32 candlepower 120 volt carbon, stereopticon 1,400
32 candlepower 40 volt, tungsten stereopticon 3i335
(special lamp)
32 candlepower 6 volt, tungsten stereopticon 3,600
(special lamp)
A concentrated light source out of focus may give poorer re-
sults than a non-concentrated light source. Consequently, it is
of extreme importance to focus the light source exactly. Practi-
cally all projectors have some means furnished to accomplish
this. To illustrate the importance of accurate focusing I
measured the maximum candlepower of the beam of a head-
light (consisting of a 16-in. parabolic reflector of 3-in. focus)
equipped with a 6-volt, 36-watt tungsten headlight lamp.
44
TRANSACTIONS 1. K. S. — PART 1
This lamp has a filament concentrated into a cylinder 1.5 mm.
in diameter by 3 mm. long. The light source was located 34 m-
(25. mm.) back of the focal point and moved forward through
it to a point 34 in- ahead, in 1/16 in. (6.2 mm.) steps. The
resultant maximum foot-candle intensities 100 ft. from the
headlight are shown in Fig. 8. Fig. 9 shows the maximum
spread from reflectors of various focal lengths with different
sized light sources. If the light source is moved too far ahead
or back of the focus, a dark spot occurs in the center of the beam.
If the light source is above the focus the beam is thrown down;
if below, the beam goes up; to the right the beam is thrown to
20
1 \
1 \
1 \
1 \
1 \
\ \
1
' T
1
I
v
1 2
1
\
1
\
\
\c
6
k
fe\
\E
Ka
%
h
\
4
0
$/if
12 3 4 5
Dl STAMCL OF LIGHT SOURCE. FROM FOCUS
SIXTEENTHS OF AN INCH
Fig. 8. — Curve showing change in maximum intensity of beam from an incan-
descent headlight (consisting of i6-in. silver-plated parabolic reflector of3-in.
focus equipped with a 6-volt, 36-watt, tungsten headlight lamp) with a change
in the position of the light source.
the left, etc. Fig. 10 shows the distribution curves of the above-
mentioned equipment with the light source located at the focus.
34 in. back of it and 34 m- to the side of it.
It has been shown that a concentrated light source can be made
to produce a powerful beam, either with a lens or a reflector. In
some instances lenses are in use ; in others reflectors. Naturally,
the question arises as to why lenses are used in one case and re-
flectors in another ; what are the advantages of one over the
porter: projection of light
45
other, etc. In general it may be said that lenses or accurately
ground glass reflectors, such as mangin mirrors, are preferable
where stray light is objectionable — such as for stereopticon lan-
terns: and where extreme accuracy is necessary — as in large
Diameter of /./fftt Joi/rce /n fixfe enter /nchej
Fig. 9. — Curve showing spread of beam from parabolic reflectors of various focal
lengths equipped with various sized light sources.
searchlights. Such work warrants the more accurate and more
expensive ground glass lenses and mirrors. On the other hand,
such applications as headlights do not require very accurate dis-
tribution of light; in fact, a little stray light in the immediate
4
46
TRANSACTIONS I. It. S. — PART I
20
—
"I
- FCC
Ab
2
A= LAMP? AHEAD 0
B-- " AT FOCUS
C= " i" BEHIND F0
us
1
\
a.
cus
/'
\
K
/
1
o
i
r
1
/Up
5
</>IO
1
1
/
i
\
i
V~
t
f
\
5 6
I
T
/
\
1
i
v
o
u.
A
i
•
VI
\
\zzi
c. _^,
JJ--
^
■^r
**=.
...i-x~
g-~^
V
9 II
FEET
Fig. io. — Distribution curves across beam of a headlight (equipped with a i6-in.
silver-plated parabolic reflector of 3-in. focus, and a 6-volt, 36-watt single
vertical helix tungsten headlight lamp) with lamp in different positions.
/.es?<s
/fef/ec/or
Fig. 11.— Diagram showing amount of light flux from a point source utilized by
a convex lens and a parabolic reflector of equal diameters.
Fig. 12.— Diagram showing amount of light utilized by a short focus and a
long focus parabola of equal diameters.
porter: projection of light 47
foreground is desirable. Nor does this class of work warrant
expensive lenses. For this service metal parabolic reflectors are
excellent.
The parabolic reflector has the advantage of covering and
utilizing a greater percentage of the total light flux. For ex-
ample, Fig. ii shows a reflector and a lens of the same diameter.
The shaded portion illustrates the total light falling on and being
redirected by each, showing a considerably greater percentage
for the parabolic reflector. It is evident from the figures that by
placing the focus deeper in the parabola — or in other words,
using a reflector of shorter focal length — a still greater per-
centage of the total light flux could be utilized.
A short focus parabola is a deep curve, while a long focus one
is shallow. Fig. 12 shows two parabolas of equal diameter, but
different focal lengths, A being short and B long. A reflects the
greater percentage of the total light emitted (Fig. 13).2
On the other hand, a short focus reflector requires a lamp of
small diameter, while the long focus allows a larger bulb — hence
a higher candlepower lamp — to be used. Assuming the size of
a light source to remain constant, an increase in its candlepower
will produce an equal increase in the intensity of the resultant
beam.
From the figures shown the thought occurs, Why not combine
a parabolic reflector and convex (or condensing) lens, and thus
- This curve sheet is made up to indicate the various mechanical properties of the
parabola and can be best illustrated by an example: a reflector for a headlight: 16 in. in
diameter. 3-in. focus; desired first to find the total depth of the parabola x. This is done
by using the lower left hand series of curves and drawing a horizontal line from a inter-
secting the 16-in. diameter curve at b\ from b the perpendicular is dropped to the line of
abscissas. It is then found that the depth is slightly over 5^ in. (13.3 cm.). It is now
desired to find the angle alpha which is one half of the total angle from the focal point
to the edge of the parabola. This is done by using the upper right hand series of curves
and drawing a horizontal line from d. intersecting the 16 in. (40.6 cm.) diameter curve at e
and erecting a perpendicular intersecting the top line of abscissas at/. The angle alpha
is then found to be 106^ deg. In estimating the efficiency of the parabola, it is very desir
able to know how much of the total light flux emitted by the lamp strikes the parabola.
This is done by projecting the line </"until it intersects the cosing curve running diagonally
across the sheet. Upon the point intersecting g a horizontal line is drawn intersecting
the right hand line of the ordinates at 0.65. This means that 65 per cent of the total light
is useful. Not only is the curve sheet useful for finding the particular values mentioned
above, but it will also serve to help estimate the dimensions of the parabola to perform
various functions.
Provided the diameter and depth of the parabola can be readily measured, the focal
length can be easily obtained, as well as the angle alpha. (By courtesy of Mr. K. W.
Mackall, General Electric Company, Schenectady. New York.)
48
■IKANSACTIONS I. E. S. — PART I
direct into one beam ioo per cent, of the light flux generated?
This could not be done, for the following reason. Light coming
from the focus of the lens would be refracted in parallel rays;
coming from some other point, it would be scattered. Place a
lens in front of a parabolic reflector, and the reflector becomes
ANGLE CC
120 100 80
9 II 13 15 . n
DEPTH OF PARABOLA IN IMCHES
Fig. 13 —Physical properties of the parabola.
~R«f/ector /.ens
Fig. 14. -Diagram showing effect of combining a convex lens and parabolic
reflector on light rays from a point source.
the light source for the lens, giving a result similar to that shown
in Fig. 14. This has been done where a double beam is desired :
one narrow and powerful to reach far ahead, the other wide to
pick up objects to one side in the foreground— such as whistle
posts, etc., in railway service. Lenses and reflectors are, however,
frequently combined in this manner: A convex lens is backed
by a mirror in the form of a sphere, having its center at the light
porter: projection of light 49
source. Such a spherical mirror will re-direct the light, throwing
it back through the light source; thus increasing its apparent
intensity. Where incandescent lamps are the light sources, the
spherical mirror has an additional advantage. By throwing an
inverted image of the filament back on the filament itself, the
apparent light source becomes more nearly solid, resulting in a
more uniform field.
The first incandescent lamps to be commercially applied in
considerable use to this work were the old carbon stereopticon
lamps of 128, 200 and 260 watts capacity. These lamps had a
conical shaped spiral filament and operated at an efficiency of 3.94
watts per candle. Similar lamps of 64 and 128 watts, at 4 watts
per candle, were also put out for street car headlights. The fila-
ment was wound in a conical spiral, in order to concentrate it
as much as possible (Fig. 18).
Fig. 15.— Focusing headlight lamp.
With the introduction of the drawn-wire tungsten filament
lamp, operating at a much higher efficiency than the carbon, and
obtainable in considerably greater capacities, the scope of the
incandescent projector was enormously enlarged. Not only were
these lamps available in much higher wattages than carbon, but
the filaments could be concentrated to a much greater degree.
Operating at a remarkable advance in efficiency over the carbon,
further increased their advantages for this class of service. The
production of lamps varying from very low to very high candle-
powers offered light sources for almost all forms of projection
apparatus.
The first field to apply these lamps was that of automobile
50 TRANSACTIONS I. E. S. — PART I
headlights. Six-volt lamps of various candlepowers were devel-
oped. The filaments of these lamps took the form of a double
helix, i. e.t screw shaped, in order to give sufficient spread to the
beam to cover the road (Fig. 15). The first large lamp made
was a 100-watt, no-volt stereopticon lamp. The filament of this
lamp was wound into a closely coiled helix of small diameter and
this helix in turn rewound in such a manner as to concentrate all of
the light source of the lamp into a cylinder 8 mm. long by 8 mm.
in diameter. This lamp is made in a round bulb 2>Ya in- (9-52 cm-)
in diameter (Fig. 16). Lamps of this type are commercially
available in 100, 250, 500 and 1,000 watts capacity, though the
latter lamp has not yet been standardized. Experimental lamps
Fig. 16.— Focus type tungsten-filament stereopticon lamp for 105-125 volt service.
have been made of considerably higher wattage, and at a very
high operating efficiency.
The low-voltage lamps can be made with much more highly
concentrated filaments, due to the short thick wire used and,
therefore, require less wattage to produce the same beam intensity.
The filament of a 6-volt, 108-watt headlight lamp occupies a
cylinder 2.5 mm. in diameter by 5 mm. long; while that of a
100-watt, uo-volt stereopticon lamp is 8 x 8 mm.
The field of application of these concentrated filament lamps
is very large, starting with the low voltage lamps of which an
enormous number is used for headlight service (headlights for
all sorts of purposes, particularly automobiles, motor boats, aero-
planes, fire fighting apparatus, etc.) ; and as portable lamps for
porter: projection of light
5i
small searchlights, small spotlights, theatres, etc. At first one
thinks of a 6- volt battery lamp as of rather small capacity, yet
several thousand 6-volt lamps are now in use by one of the large
railroads for headlights. The lamps are 108 watts capacity, 150
candlepower, and have a highly concentrated filament. In a
20-inch (50.8 cm.) silver plated parabolic reflector, this type of
lamp produces a beam of over 900,000 candlepower — sufficiently
powerful to discern objects over 2,000 feet away.1
Fig. 17.— Tungsten-filament, focus type headlight lamps.
Many locomotives are already equipped with 30-volt generator
sets, with which arc headlights were previously used. Thirty-volt
concentrated filament lamps have been developed of 100, 150 and
250 watts capacity, to enable the operation of incandescent head-
lights from these generators (Fig. 17). A special lamp of 1,500
candlepower in this voltage is also available, to meet the rather
extreme law in some states, requiring locomotives to carry head-
lights of 1,500 unreflected candlepower.
3 Schrugham J. G., Electric Headlights; Journal of Elechicity, Power and Gas,
February 7, 1914, p. 125; Minick, J. X... The Locomotive Headlight: Trans. I. E. S., vol.
IX Xo. 9.
52 TRANSACTIONS I. K. S. PART I
The incandescent head-lamp has many advantages, such as
ease of control, steadiness of beam, simplicity, reliability, etc.,
which make it especially applicable to this class of service. Vari-
ous tests have shown that for equal beam candlepowers the in-
candescent headlight will pick up objects at considerably greater
distance than the arc headlight. This is probably due both to the
color and steadiness of the light from the incandescent lamp.
Another large field of application for the low volt concentrated
filament lamp is in signal work. The railroads are experimenting
with the so-called "daylight position signal." The indications of
these signals are given by three rows of lenses at 90, 45 and o
deg. positions. Each lens is backed by a low candlepower
concentrated filament lamp and either the o, 45 or 90 deg. row
is lighted, depending upon whether the signal is stop, slow or
proceed. It is claimed that even under the trying conditions of
looking at the signal toward the setting sun it is visible from
a greater distance than the regular semaphore blades. The day-
light position signal eliminates moving semaphore blades and pre-
vents possible mistakes through color blindness of engineers, or
color changes due to atmospheric conditions. If the trial installa-
tions prove as satisfactory as expected, this method of signaling
should be widely applied.
Another field in which the lamps have been used is for light-
ships and range lamps having a low candlepower, highly con-
centrated filament, backed by a silver plated parabolic reflector.
Lights from these lamps have a distinctive color and sparkle and
are visible at great distances.
Experiments are being made with small lamps and dry bat-
teries for heliograph signals. Lamps of about 0.5 candlepower,
2.7 volt, backed by 5-in. (12.7 cm.) mirrors, operated by small dry
batteries have successfully been read at night without the aid of
glasses from a distance of 12 miles (19.3 km.).
The big commercial demand for focusing filament lamps, how-
ever, will probably be in the 105-125 volt class. Here the number
of applications is very large. I will simply touch on some of
the principal ones. Chief of these at present is stereopticon
work. An incandescent lamp makes a stereopticon lantern safe,
simple and clean, so that it can be operated anywhere, by any-
Fig. iS (Reading from left to right).— 1-32-cp., 240-volt regular carbon lamp; 2-32-cp., 240-
volt carbon stereopticon lamp; 3— 32-cp., 120-volt carbon stereopticon lamp; 4-32-cp
40-volt tungsten-filament stereopticon lamp; 5-32-cp., 6-volt concentric helix tung-
sten-filament lamp.
Fig. 19.— Building frout illumination with one 500-watt tungsten stereopticon lamp in
16-in. parabolic reflector of 3-in. focus.
Fig. 20.— Morgan memorial library, Hartford, Conn., illuminated by four 500-watt tutu
sten stereopticon lamps in parabolic reflectors located across the street.
Fig. 21. — Billboard lighted by one 500-watt tungsten stereopticon lamp in a
16-in. parabolic reflector of 3-in. focus 250 ft. away.
porter: projection of light 53
body. A lecturer is not bothered by the operator forgetting to
regulate the feed of his lantern, or by the humming or hissing
noise inherent in most of the powerful lanterns ; in fact, numer-
ous advantages are gained. For the small lantern, sign pro-
jector, etc., the 100-watt lamp is ample. For larger lanterns,
such as used in small auditoriums and lecture rooms, the 250-watt
is preferable. As these lamps are in the same size bulb, they are
interchangeable. The 500 and 1.000-watt stereopticon lamps
have been developed to take care of larger lanterns. The lamps
should always be used with a spherical mirror, thereby increas-
ing the intensity on the screen at least 30 per cent, and also ob-
taining a more uniform field. The 500 and 1,000-watt lamps are
also satisfactory for small moving picture machines.
No satisfactory lamp is yet available for the large commercial
motion picture machine, but lamps of very high candlepower
are being experimented with, and it is hoped these used with the
proper mirrors and condensing lenses will be successful. Their
adaption to moving picture machines would largely reduce the
fire risk, and eliminate synchronism troubles in motion picture
theatres supplied with alternating current.
For playhouse lighting, focusing filament lamps have been
successfully used as floodlights and for lighting drops. The ease
and steadiness with which they can be dimmed any desired
amount enables sunrise and sunset effects not practical with
other illuminants.
A field which is just opening and promises to be large is that
of floodlighting of building surfaces and painted signs. Many
buildings, beautiful pieces of architecture, cease to attract with the
approach of darkness, simply because they cannot be seen. Figs.
18, 19, 20 and 21. By the use of 500- watt tungsten stereopticon
lamps and parabolic reflectors, it is a fairly easy matter to flood
them with light from the roofs of neighboring buildings, or any
convenient location, and make them stand out in all their beauty
after dark ; causing them to appear even more conspicuous than
in daylight, by contrast with the surrounding darkness. Fre-
quently signs painted on water tanks, walls of buildings, chim-
neys, etc., or regular billboards, are so located as not to be easily
accessible to current supply or are difficult to wire. These can
54 TRANSACTIONS I. E. S. PART I
be effectively lighted at night by projecting light onto them from
distances of several hundred feet; thus greatly lengthening their
advertising value at a low cost. At night they become more at-
tractive than during the day, and can be read from considerable
distance. Advertising banners, flags, etc., have been similarly
lighted to advantage. This is a most excellent field for central
stations. The load is steady, the hours of burning are long, and
the installation is simple. The class of service does not conflict
with the regular electric sign. Flood lighting is generally applied
to such signs as are visible from other and more distant portions
of a city than the electric sign on the main business street; and
on account of its low installation cost and easy maintenance, it
can often be installed where it would be impossible to sell a reg-
ular electric sign.
cassidy: art and science in home lighting 55
ART AND SCIENCE IN HOME LIGHTING.*
BY GEORGE W. CASSIDY.
Synopsis: Some of the factors and conditions which influence the
design of lighting systems for moderate priced suburban or country homes
are discussed in the following paper. The author suggests methods for
lighting various rooms of homes costing from $5,000 to $15,000.
The proper lighting of the home has become a very important
subject in recent years from two standpoints, namely, the esthetic
and the scientific. A broad and comprehensive knowledge of
both these phases is required if satisfactory results are to be
obtained in practise.
As to the different points governing good lighting of the home,
almost as many expert opinions have been expressed as there are
different kinds of lighting, each statement being based on the
individual point of view of the lighting expert.
The illuminating engineer whose training has been essentially
scientific, although he may have the artistic temperament, when
it is necessary to compromise between what is scientific and what
is purely esthetic in a given case, is almost sure to tip the scales
in favor of the scientific. The same argument applies vice versa
to the architect or designer whose training leads him to give the
greater weight to the esthetic side.
I doubt whether in most cases the best results can be obtained
except by the cooperation of the architect and the lighting engi-
neer. For instance, a lighting engineer asked me to cooperate
with him in designing a table lamp which should be essentially
beautiful and at the same time efficient both for reading and as
medium for general illumination. It was specified that the lamp
should be equipped with a 250-watt distributing, mirror reflector
for the indirect light and four direct lamps properly shielded by-
diffusing glass for reading ; also the indirect equipment should be
outside the field of vision of a tall person coming into the room.
Our first attempt was a flat failure from the artistic side, as the
silk shade portion had to be made on the graceful curves and gen-
* A paper read at a meeting of the New York Section, Illuminating Engineer
ing Society, December 10, 1914.
™;Ji?C I",imina]ing Engineering Society is not responsible for the statements or
opinions advanced by contributors.
56 TRANSACTIONS I. E. S. — PART I
erous proportions of a barrel. A number of compromises were
then made, the most important being the reduction of the size
of the lamps from 250 watts to 150 watts. This change so
reduced the dimensions of the shade that a well designed lamp
was possible both from the artistic and scientific standpoints.
To illuminate a home properly, the lighting must be consid-
ered from the esthetic, physiological, psychological and econom-
ical standpoints. From that old saying, "a man's house is his
castle," one knows that every man desires to have his home as
beautiful as his means will afford and as his taste dictates.
Therefore the primary requirements is that the lighting should be
esthetically correct ; the fixtures should be designed to harmonize
with the decoration of the respective rooms. Most homes to-day
have lighting fixtures which are esthetically correct.
In taking up the second consideration one is confronted with
an entirely different condition. How many homes even approach
being correctly lighted from the physiological standpoint? The
change in the type of illuminants in the last few years has placed
a much greater emphasis on the physiological side of the ques-
tion not only from the increase in intensity of the light but also
from the decided change in color. Instead of the soft yellow
light of the carbon lamp, one must now contend with the hard,
cold white light of the tungsten lamp.
This point was particularly forced on my attention while I was
walking through some of the prominent streets of my home town
when I saw the large number of houses which were lighted with
brilliant and glaring tungsten lamps. If these lamps were not of
the frosted, ball type, they were shielded by some form of frosted
shade which is a good medium to show just where the filament
has its brightest point.
From an ocular hygienic standpoint, it is very easy to under-
stand why a great majority of the people of to-day are com-
pelled to wear glasses and why there is so much suffering from
eyestrain.
The third consideration, the psychological, is also of great
importance for it has to do with the effect light has on the mind.
I will not take time to go deeply into this phase of the subject.
However, there is no question that certain kinds of lighting will.
cassidy: art and science in home lighting 57
as the saying goes "get on one's nerves." For illustration, the
improper use of semi-indirect or indirect lighting in the home.
One's first impression on entering a room lighted by either of
these systems is the lack of glare; but after sitting in the room
for a while one often wonders why the ceiling seems so low ; or
why a beautifully carved table or chair does not seem to have
the proper perspective, for the slight shadows they cast are from
an unnatural angle ; there is a spectral look to the objects in the
room. In other words, the whole room looks flat; it lacks the
correct balance of light. I will later explain this effect in a
specific case.
It is also a known fact that color is an important factor from
the psychological standpoint and applies particularly to white
lights. Just how the nerves or mind are affected is a question
that comes within the province of the psychologist. Personally,
I know of a number of cases where the effect of white lights,
I mean white light of the ordinary tungsten lamp, concealed in
ground glass shades, has caused the person to be depressed or
have the blues.
In lighting a house the problem should be taken up first from
the practical side and not the artistic or esthetic. Often the
outlets are placed without regard to the purpose for which the
room is to be used. It is very important to study the specifica-
tions carefully, to learn the area of the room, the height of the
ceiling, the general decorative scheme and particularly the pur-
pose for which the room is to be used.
Knowing the use of the room, one can readily decide upon the
foot-candle intensity, place the outlets, and determine the proper
amount of wattage, etc.
I have tried to describe in a general way the most important
principles which should be borne in mind when a problem of
home lighting is being considered. For a more comprehensive
understanding of a number of the points already mentioned, it
will be better to mention the actual conditions encountered by
giving a particular case: the proper lighting of a modern sub-
urban or country house costing from $5,000 to $15,000. Such a
house usually has an entrance hall, living room, den or music
room, dining room, kitchen and pantry on the first floor and
sleeping and bath rooms above.
58 TRANSACTIONS I. E. S. — PART I
Entrance Hall. — Frequently this room is given little or no
attention as far as correct lighting is concerned — ''just a light,"
many owners seem to think, is sufficient. And yet one's first
impressions of a home are obtained from the appearance of this
room. Very often the first thing to be seen is the typical hall
lantern with its glaring lamp. I do not think I exaggerate when
I say that a very large percentage of all houses to-day have halls
lighted in this manner.
Suppose the following specifications for this hall : dimensions
1 6 ft. long, 10 ft. wide and 9 ft. 6 in. high, with colonial treat-
ment. The stairway is situated at the rear end. The wood-
work is to be white with medium colored walls and light buff
ceiling.
The first question to determine is the approximate intensity
of the illumination required. There should be an intensity of
at least 1 to 1.5 foot-candles. Uniformity here is not at all
necessary ; however, there should be no dark corners. The
amount of light required will be determined by the color of walls
and ceiling, and the absorption of the glass employed.
Having determined the light intensity, the position of the out-
lets is the next problem. In this particular case there should be
one ceiling and two bracket or side-wall outlets. The ceiling
outlet should be in the middle of the room and the side outlets
arranged to balance properly. For economical reasons the ceil
ing outlet should be wired for two circuits ; one for the night light
and the other for general illumination. For convenience the
lamps should be controlled from the second floor as well as from
the first floor.
To illuminate this room and stairway efficiently from a single
ceiling outlet, it would be necessary to increase the power of the
illuminant to a point where the intrinsic brightness would be very
annoying. By distributing the lighting units and using smaller
illuminants shielded by properly designed shades, made of tinted
diffusing glass, or by amber colored lamps, the glare would be re-
duced to a minimum. With this foundation, the designer or
decorator, can readily design fixtures which will harmonize with
the period or decoration of the room.
cassidy: art and science in home lighting
59
When little thought is given to these scientific principles, the
fixture designer's efforts may often be spoiled because the fix-
tures lose their identity in their environment simply because of
excessive glare from the lamps.
Living Room. — In lighting this room, there are several very
important points which have a bearing upon the success of the
lighting scheme. The first and most important point is this : here
the family lives and in the evenings they must live with the light-
ing provided. In a great many cases this seems to require an
effort.
Fig. i. — Fixture for general illumination in a living room.
Suppose the following specifications are those of a typical
living room : dimensions : 24 ft. long, 18 ft. wide and 9 ft. 6 in.
high; wood trim of flemish oak; walls a medium brown, and
ceiling light buff.
I have already placed emphasis upon the fact that the purpose
for which the room is to be used is very important. The living
room is used for several purposes ; therefore the lighting scheme
must have flexibility. In addition to being the library of the
60 TRANSACTIONS I. E. S. PART I
home, it is often used for festive occasions. There are other
times when members of the family simply desire to sit around
and converse. To meet these conditions it is necessary to supply
at least three different lighting arrangements. In placing the
outlets the decorative arrangement must not be lost sight of, even
though a compromise is necessary. In order to keep the intrinsic
brightness reduced to a minimum there should be two ceiling
outlets, one in the center of each half of the room. This arrange-
ment will give a more even distribution of light and a decided
reduction of glare.
With a light intensity approximating three and a half foot-
candles, a high general illumination is assured which will suffice
for card playing, dancing and special occasions. For average
conditions a one and a half foot-candle intensity will be enough.
In order to accomplish this in the best way, each fixture should
be wired with two circuits, the higher candlepower lamps on
one and those for the lower intensity on the other.
Before considering the type of lighting fixture to be suggested,
it will be well to briefly define the three forms of illumination in
common use at the present time, namely, direct, semi-direct and
indirect.
A direct lighting fixture throws most of its light directly to
the floor and walls ; only a small percentage of the light reaches
the ceiling. A semi-indirect fixture reflects the greater per-
centage of its light to the ceiling from which it is diffusedly
reflected downward ; a smaller percentage of the light passes
through a glass or translucent bowl. An indirect fixture reflects
all the light to the ceiling from which it is diffusedly reflected
over the room.
Consider first the usual semi-indirect lighting unit. The height
of the ceiling being 9 ft. 6 in., the maximum distance of the top
of the bowl from the ceiling cannot exceed 2 ft. 4 in. because with
a bowl 6 in. deep the fixture would hang 6 ft. 8 in. from the floor.
From the esthetic viewpoint, this type of fixture in this room
would be bad practise because the distinctly bright spots over
the fixtures would be the most conspicuous points in the room.
With a ceiling 11 or 12 ft. high a semi-indirect fixture or an
indirect fixture with a luminous bowl can be hung far enough
cassidy: art and science in home lighting 61
below to give a wider and more even distribution to the light and
thereby overcome the objectionable effects of light spots. This
defect could also be softened and the light balance restored by
the use of one or more table lamps or by incorporating side
brackets in the decorative scheme. These same objections would
apply to the indirect unit.
Esthetically, the use of the indirect fixture in the home is in-
correct unless designed with a luminous bowl; otherwise, with
the opaque bowl, the body of the fixture forms a very sharp con-
trast with the lighted ceiling.
The most commonly used fixture in living rooms is a direct
lighting type of the multiple unit or shower design. The glass
manufacturers have put on the market a great variety of shades
to be used on fixtures of this type. They have recognized the
fact that by artistic etching and tinting, in the ivory tones, they
have been able to produce an article which is effective and at the
same time eliminates an appreciable amount of the glare, and
there is no question but that the results obtained by the use of
this glassware is a step forward. These shades should be long
enough to conceal the lamp. Considerable caution must be exert
cised also in the selection of illuminants. If the conditions are
such that a high intensity of light is required as in the present
case, the filament of the lamp will be visible as a distinctly bright
spot on the shade owing to its closeness to it.
I have now described three different types of fixtures and ap-
parently Avithout arriving at a satisfactory result. Therefore
a compromise suggests itself : the blending of the desirable fea-
tures of direct and semi-indirect lighting. By designing a fixture
of the glass bowl type, equipped with an opal cover, one may
obtain a unit which will transmit a soft diffused light to the
ceiling without spotting, while a good percentage of the direct
rays will pass through the bowl. By reducing the ceiling illum-
ination and utilizing the direct rays, the effect of flatness in the
room may be avoided and the natural perspective and shadows
of objects retained. Care must be taken in placing the lamp
within the bowl to have the filaments sufficiently distant from
the side to prevent the appearance of bright spots and to permit
the light to be properly diffused through the glass. Glass afford-
62 TRANSACTIONS I. E. S. — PART I
ing a maximum diffusion and the minimum of absorption should
be used. This type of fixture will overcome many of the defects
which are objectionable from a physiological standpoint.
Artistically and psychologically it is still defective, in that the
room lacks color and a correct balance of light. By this latter
term I mean a distribution from other sources in the room such
as softly lighted lamps on side brackets or portable lamps so ar-
ranged or placed as to bring out the important points in the
scheme of decoration.
Supplemental lighting is of course more or less extravagant
and where economy is essential it can be omitted with possibly
the exception of the table lamp.
I have mentioned in a general way, the desirability of the use
of color in the lighting of the home. It is regrettable that more
emphasis has not been placed on this part of the problem by
those interested in artistic lighting and also those who approach
lighting problems from the engineering side. I have heard and
read statements made by lighting experts that the ideal arti-
ficial light is that which most closely resembled natural daylight
in color and diffusion. I consider this statement entirely too
broad and in need of qualification. Daylight is the ideal light
medium in all manufacturing pursuits, office work, draughting,
color matching and many other commercial enterprises. I may
be making a rather radical statement when I say that daylight
as it comes from the heavens is not the ideal light for lighting
the home. The really artistic home should be esthetically lighted
under daylight conditions as well as under artificial light.
The interior decorator studies his problem from many angles,
two of the principal ones being light and color; and if daylight
is the ideal light, why does he use so much color in the window
hangings, portieres, etc., and at times even shut it out entirely?
It is to improve upon daylight, to obtain color and pleasant light-
ing effects and shadows.
Therefore, if daylight lacks color, and artistic warmth, why
should one strive to imitate it for the home. The present il-
luminants have already reached beyond the limit of good light
for home use and need modification for the best results.
There are available several materials suitable for producing
cassidy: art and science in home lighting 63
color effects in decorative lighting such as silk, gelatine and glass.
I have been informed that one of the large lamp manufacturers
has already perfected a method by which regular sized lamps
can be made of amber colored glass and put on the market as
standard lamps.
I have said that the fixture I have described as the most suit-
able for the requirements of the living room lacked color.
Ophthalmologists and oculists have agreed that amber light is
preferable to other colors. By tinting the glass bowl a yellow
tone, and by the use of light amber glass lamps or color caps on
incandescent lamps giving white light, it is possible to produce
the soft warm and hospitable effect so necessary to bring out the
real fineness of the decorative scheme of the room.
The practical engineer will in all probability say that such a
scheme sacrifices economy. This is true, but economy is of sec-
ondary importance when compared with the artistic results and
ocular comfort. Ocular hygiene may well be a primary factor in
the lighting of living rooms. It is unfortunate that there are so
few table lamps on the market to-day which combine the scien-
tific and the esthetic requirements. Many of these lamps are
artistic ; some few scientific ; but a combination of the two is al-
most wanting.
In order to demonstrate more clearly the important points
necessary to be borne in mind when designing an efficient table
lamp, I will exhibit a lamp (Fig. 2) which I believe meets the re-
quirements of a living room. It possesses the three essential fea-
tures of good lighting : first, it is artistic ; second, it is efficient as
a reading lamp; and, third, it has flexibility. By turning one
switch, one may connect indirect light which evenly illuminates
the whole ceiling with a soft amber glow. By the turn of a
second switch, two more lamps illuminate the silk shade which
diffuses a soft light over a large area of the floor. This is neces-
sary to give the correct balance of light in the room. Under day-
light conditions most of the light coming through the windows is
distributed on the floor and there is a balance between the bright-
ness of the ceiling with that of the floor. This is the natural con-
dition of light direction which mankind has been accustomed to
for generations. With a third switch the two remaining lamps
64
TRANSACTIONS I. E. S. PART I
which are utilized for reading purposes may be lighted. These
switches also conduce to economy in the use of the lamp. In
selecting the mirror reflector for the indirect light equipment, I
have taken the concentrating in preference to the distributing
type, because the amber colored disk will distribute to a certain
extent. Care must be taken to prevent the light distribution
from going beyond the stop line. In most rooms this would be
at the picture moulding ; and, where this is omitted, the proper line
would be at the junction of the wall and ceiling. In the arrange-
ment of the direct lamps the filaments are so placed that the
Color - correcting
Firfer
Reflector
Diffusing bovwf
Fig. 2.— A table lamp for a den or for local lighting in a living room.
highest point will form the apex of a right angle with a line
drawn from the maximum reading distance which is approxi-
mately 3 ft.
The diffusing shade which is made of alabaster acided glass is
so designed that its general curvature is somewhat parallel with
the filament of the lamp. This is necessary to assure the great-
est efficiency of the diffusion as no reading lamp is efficient with-
out such diffusion.
If the light rays are not diffused either by the interposition
of the proper kind of glass or by indirect reflection from a
cassidy: art and science in home lighting 65
light colored non-glazed or mat surface, specular reflection from
the book or paper which one may be reading is bound to cause
eyestrain.
Den or Music Room.— Suppose the specifications of a room
are 14 ft. long, 12 ft. wide and 9 ft. 6 in. high; medium dark
walls and light buff ceiling. A room of this type can be correctly
lighted by a table lamp similar to the one described in the lighting
of the living room. Fixtures or bracket lamps are not required
but the use of wall lamps may enhance the decorative treatment.
If used they should be equipped with lamps of very low candle-
power, not over 10 watts; and in selecting the light shields,
whether of glass, silk or other fabrics, a low translucency is es-
sential. If the room is used as a music room, it is only necessary
to increase the size of the illuminant of the indirect portion of
the lamp to obtain the proper amount of illumination. If for
economical reasons this is not practical, the lighting scheme must
be supplemented by a properly designed local light at the piano.
Dining Room.— I approach the problem of what constitutes
correct lighting of the dining room with considerable reluctance.
I presume that of all the rooms in the house the dining room is
lighted by the most diversified methods. There is no question
about the flexibility of the lighting arrangements in this room.
Specifications: dimensions, 18 ft. long, 15 ft. wide and 9 ft.
6 in. high. Ivory colored woodwork, medium straw colored
walls, and light buff ceiling. Architecturally, such a room may
be called colonial. I have mentioned the color scheme to demon-
strate the direct relation between the lighter or darker colored
walls and ceiling and the light intensity. Dark toned rooms
absorb more light and therefore require a higher candlepower in
the illuminant.
The placing of the outlets depends upon the system of light-
ing to be installed.
Decorators and architects have used with success, from the
artistic as well as the good lighting standpoint, side brackets
around the room, the light source being properly shielded and
supplemented by a candelabra on the table. A room of the
dimensions given would require at least six two-lamp side
brackets having low candlepower lamps of not over 10 watts
66
TRANSACTION? I. E. S. — PART I
each. This would give a fair general illumination without annoy-
ing glare, but it would be necessary to have them all lighted or
there would be dark corners or spots upsetting the esthetic effect
and also spoiling the correct lighting scheme. This arrangement
would not be economical in the moderate priced residence here
considered.
Another method of lighting a dining room which has been very
extensively used is the so-called glass dome fixture. This is a
Fig. 3.— A fixture for a dining room.
fixture designed with a large glass dome suspended by a chain
or stem over the table. From the decorator's point of view it is
particularly bad. It breaks into the symmetry of the room and
lacks proportion to its surroundings. It is the most conspicuous
object; it occupies a position which compels it to dwarf every-
thing around it ; it also prevents the artistic arrangement of
floral decorations. From the physiological side the dome light-
CASSIDV : ART AND SCIENCE IN HOME LIGHTING 67
ing fixture is far from desirable. The table cloth is so brightly
lighted that there is a decided glare. A very simple experiment
will demonstrate this point. If the cloth is suddenly removed
from the table, the effect will be as if some of the lamps had been
extinguished, for the room will seem almost dark. The table cloth
has acted as a diffusing medium for the direct light under the
dome. If doilies are used instead of the cloth, one is likely to
be troubled with specular reflection from the polished surface of
the table. It is possible to reduce the extreme brightness upon
the table by the use of some diffusing medium such as a silk disk,
but even with this precaution, the glare is not entirely eliminated
because the source of illumination is so near the surface of the
table.
Another objection to the use of the dome fixture is the fact
that those seated at the table are constantly looking from a light
to a dark zone and vice versa. Each change of the direction of
the gaze under such condition causes continual dilation and con-
traction of the pupil with its consequent visual fatigue. This
defect can be overcome of course by the use of side brackets or
ceiling fixtures, but the addition would not be economical.
As the specifications of this dining room do not call for a
beamed ceiling, one might place the outlet in the center of room
and install a semi-indirect or indirect fixture to suit the con-
ditions.
As the ceiling is 9 ft. 6 in. high, and because the light source
is placed over the table, it is possible to hang the fixture only
5 ft. 6 in. from the floor. This would leave sufficient distance
between the ceiling and the top of the bowl to permit of a wide
distribution of the light and eliminate light spots on the ceiling.
1 his overcomes the artistic defects apparent under the other con-
ditions. By the use of an amber colored disk over the bowl of
the fixture, the white light from the tungsten lamp may be
changed to soft warm tones, which will improve the beauty of
the artistic scheme of the room. To eliminate whatever flat
effect of diffused lighting may exist, it is only necessary to add
outside direct light units arranged around the glass bowl of the
semi-indirect fixture or the opaque bowl of the indirect fixture
according to the taste of the designer. This addition will correct
68 TRANSACTIONS I. E. S. — PART I
the light balance by giving to the surroundings light and shadow.
In providing against the physiological defects of such a fixture,
thought must be given to the design and color of the glassware
or silk. The glass should be properly tinted with a yellow tone
and if silk is used amber and champagne colors are preferable.
Care must be exercised in lamping the fixture. The outside direct
lamp units must not exceed 10 watts while the inside lamps must
be larger but not to exceed 60 watts.
By this arrangement the center lamp will give the necessary
general illumination and the outside lamps the supplementary.
For the sake of economy it is a good plan to have the wiring for
two circuits.
In clearing or setting the table it is not essential that all the
lamps be lighted. In the design of the silk shade of the lamp
which I have shown, considerable compromise has been made.
In the purely technical design, the line representing the side of
the shade should form a somewhat wider angle so that the side
of the shade would be parallel to the line of vision of the average
height person sitting at the table, to avoid the possibility of any
glare. The flange at the bottom leaving a 4 in. opening pre-
vents a person seated at the table from seeing the lamps and the
glare from the reflecting surface.
The lamps within the silk shades are equipped with amber
colored disks and as a result a beautiful soft warm light is cast
evenly over the table. The opaque bowl contains the indirect
lighting equipment over which is placed an amber plate. This
type of fixture combines general illumination with the local light-
ing over the table and at the same time adheres to the important
principles of good lighting.
Where service lighting is required, such as in kitchen, pantry
and etc., fixtures placed as closely as possible to the ceiling, and
therefore above the line of vision, are recommended. The shades,
preferably opal glass frosted on the inside and of the distributing
type, should be about 7 or 8 in. in diameter and with depth enough
to hide the lamp.
In some instances a side wall lamp is required ; in that case
the bracket should be equipped with a rather dense opal glass,
deep enough to cover the whole lamp, the lamp, of course, being
placed up or down according to the position of the outlet.
cassidy: art and science in home LIGHTING 6Y)
Regarding the proper lighting of a bed room, efficiency and
economy are the essential features to be considered. By placing
one outlet in the center of the room and one over the dresser,
it is possible to obtain good results. A fixture placed close to
the ceiling, having a lamp housed in an artistically etched and
yellow tinted distributing type of shade, from 7 to 8 in. in diam-
eter with sufficient depth to cover the lamp, is often quite satis-
factory. The interior of the shade should have a roughed or
mat surface in order to diffuse the light properly. As the fixture
is placed well above the line of vision and the distance between
the filament of the lamp and glass will be sufficient to eliminate
spot glare from the filament, good general illumination without
glare and at the lowest cost will be obtained. The fixture can
be artistically designed and installed at a very small cost. The
dresser light should be suspended over the middle of the mirror
and 10 to 12 in. in front. Five feet ten inches from the floor is
the average height for a fixture of this type. This, however, is
more or less optional according to the conditions. In the main, the
specifications of the ceiling fixture will apply in this case, with
the exception that the shade, if made of glass, must be so tinted
as to prevent glare. This is very important as the shade is
directly within the line of vision. A silk shade is preferable to
a glass one for this reason, as well as for the better artistic effect.
As the light is directly from above, a woman will have no diffi-
culty in arranging her hair according to the latest vogue. The
light being well diffused within a considerable range, there should
be no difficulty in seeing well.
There are one or two points in regard to bathroom lighting,
especially interesting to the man of the house, which it is well to
mention. Most bathrooms in moderate priced houses have medi-
cine closets with mirror doors. The men members of the family
use this mirror when shaving. A large number of people do not
know that in order to see well before a mirror by artificial light
the mirror should be in shadow, so that the face will receive the
greater flux of light. By having a bracket outlet placed on each
side of the medicine closet and approximately 5 ft. 6 in. from the
floor, which is the average height of a man's face, the light source
will be in a line with the face and the best results from the light
will be obtained. The shades should be of some good diffusing
/O TRANSACTIONS I. E. S. — PART I
glass about 5 in. in diameter, deep enough to shield the light source,
and hemispherical in design. This type of bracket unit may be
termed semi-indirect as the larger percentage of the light is
reflected to the wall and ceiling and serves for the general light-
ing of the bathroom.
I have tried in this paper to add the scientific element to that
of the esthetic in the lighting of a moderate priced house and to
show how one modifies the other. The results illustrate a state-
ment in the beginning of the paper that good home lighting is
more or less a compromise.
DISCUSSION.
Mr. A. L. Powell: The statement in the paper that "the
illuminating engineer is likely to tip the scales to the side of the
scientific" may be entirely correct from the decorator's position;
yet those of us worthy of such a title will do our utmost to make
the home comfortable while at the same time striving for the
proper artistic effect. So, from a humanitarian standpoint, even
if we do give more weight to the serviceability of the lighting, we
are on the safe side. 1 believe that the average individual really
does not know a great deal about esthetics, but he certainly can
tell when his house is agreeable and healthful. All too often
are the fixtures artistically correct when viewed by daylight ; but
at night cannot be so designated. In a broad sense anything
artistic is comfortable.
Another statement that I hardly believe justified is, "Instead
of the soft yellow light of the carbon one must now contend with
the hard cold white light of the tungsten lamp." It is true that
the light from a carbon filament is somewhat more yellow than
that from a tungsten filament, but it is safe to say that there is
as much glare from the carbon lamp as ordinarily installed, as
from the latter, and glare is the important factor. For instance,
there are millions of carbon lamps in use on multiple arm fixtures
only partly surrounded by some sort of a non-diffusing shade,
throwing the light directly into one's eyes. In many cases where
tungsten lamps are substituted changes are made in the glass-
ware or fixtures, or both ; so on an average the tungsten lamp
installation is not as much more harsh as might be imagined.
ART AND SCIENCE IN HOME LIGHTING Jl
Following this line of reasoning, it is doubtful if a semi-in-
direct or totally indirect fixture, no matter how improperly ap-
plied, will ever "get on one's nerves," as much as the great
majority of direct lighting fixtures. While on this subject of
comparative value of various illuminants, it seems a rather broad
conclusion that the slight difference in color between the carbon
and tungsten lamps should be sufficient to cause a person to be
depressed or have the blues. One might follow this train of
thought and arrive at the conclusion that daylight would be much
more likely to cause such an effect than the yellowish artificial
light.
To me a room does not necessarily look flat if indirect systems
are properly employed, and I am sure many of us have all seen
very beautiful rooms with these types of units. It may be true
that an indirect fixture with the loose bowl is artistically incor-
rect, yet in this connection I might mention a little personal ex-
perience. While even now I am not an exponent of indirect
lighting applied everywhere, sometime ago I was not at all cer-
tain as to the relative merits of the three types of fixtures, so I
installed in my home all three systems, direct, semi-indirect and
totally indirect, and lived under them for over a year. The
living room is lighted from a semi-indirect bowl with an amber
dipped lamp within. The light is well diffused. The den is
lighted by a totally indirect fixture with a tungsten-filament
lamp. The chairs and other surroundings in the two rooms are
equally comfortable and there is no reason why we should use
one room in preference to the other, yet when we sit down to
read or stay around for any length of time we almost invariably
go under the indirect lighting.
The author at one point in the paper states that too little at-
tention has been paid to the color of the light. I believe that
illuminating engineers take full account of this in designing the
lighting for a residence and provide tinted lamps or tinted glass-
ware wherever it seems advisable.
I cannot see how ophthalmologists and oculists could agree
that amber light is preferable to other colors. If this is true,
certainly any of the incandescent artificial light sources would be
more generally desirable than daylight. Possibly color of light
72 TRANSACTIONS I. K. S. — PART I
and intrinsic brightness have incorrectly been used synonymously.
We will all agree that a diffused light is extremely desirable.
Throughout the paper the author recommends amber tinted
light for almost every room. This is a matter of personal
preference, but it seems to me that it is largely dependent on the
finish of the room. For instance, I would question the advis-
ability of using amber tinted shades in bedrooms, save those
decorated in color harmonizing with this tint. My experience
and observations have indicated that the average bedroom is
papered with some sort of light blue or light pink flowered
decoration, with possibly a light purple or green, or some other
dainty figure. There is glassware available in commercial forms
which has, for instance, a light blue medallion on an etched
white background, or pink flowers with delicate green leaves on
the white glass. One may choose among these glassware to
match almost any scheme of room decoration. They are attractive
and fit in so well with the room treatment that a most pleasing
effect is secured.
I will grant that the dome in the dining room may be incor-
rect from a decorative standpoint, yet a great many persons with
whom I have talked upon this subject favor such an arrange-
ment of light. For the reason that the table is the part of the
room where one desires to have attention concentrated. The
hygienic objections to a dome are removed by hanging it at the
proper height and covering its base with a slightly tinted light
diffusing silk screen. The lighting should blend so well with the
general purpose of the room that one should not notice of what
the lighting consisted.
In the kitchen it does not seem desirable to use reflectors
etched on the inner surface, as there is likely to be a certain
amount of grease and smoke from the cooking and on such a
rough surface this dirt will readily collect, and it is difficult to
keep it as clean as necessary. I believe it is preferable to use a
rather dense, smooth opalescent reflector or prismatic bowl-
shaped reflector. These are particularly efficient and in the
kitchen where the lighting is somewhat of a commercial proposi-
tion. A high intensity of illumination is desired on the food as
it is being prepared, and the light must be obtained in the most
ART AND SCIENCE; IN HOME LIGHTING 73
economical manner. It is the one room in the house where
economy is the primary factor.
Mr. M. Luckiesh : I believe that if every fixture man would
attack the problem of uniting science and art or utility and
esthetics as Mr. Cassidy has done, proper lighting would exper-
ience the greatest boom in its history. The matter of proper
fixture design is one of the most serious problems the lighting
specialist has to deal with. I believe Mr. Cassidy has handled
this subject well from the standpoint of the fixture man
who has naturally been chiefly interested in the esthetics of de-
sign. The paper is a valuable one even though we all do not
agree with some of the statements. That condition is not unusual,
for we do not thoroughly agree on some of the fundamentals of
lighting. It is often difficult to unite utility and beauty, but it
must be done.
Mr. Powell stated that the average man knows when his home
is agreeably lighted. How he has found this out I am at a loss to
imagine. In the first place the "average man's" home is not
agreeably lighted. Secondly when we consider that the average
man does not know when his home is badly lighted (which is
unquestionably the case at the present time) it is difficult to see
how he would know when his home is agreeably lighted.
Regarding efficiency we must remember that, especially in the
home, the real efficiency is a measure of how well the lighting ap-
paratus fulfils its object. And we must remember that its object
is not pure utility unless we include the utility of beauty. As
Dr. E. P. Hyde expressed in the Johns Hopkins lecture course,
"efficiency is the ratio of satisfactoriness to cost and not the
reciprocal of cost"
I agree with Mr. Cassidy's statement that color is the keynote
in illumination of the home. I seriously doubt that tungsten
light "gives one the blues" any more than the carbon lamp es-
pecially in view of the fact that we work under daylight with
satisfaction many hours each day. However I believe quality
of light should be considered a matter of personal taste as long
as extremes are not indulged in. Mr. Cassidy uses amber glass
very much. He uses it over the "indirect" portion of some of
his fixtures. This light reaches the objects in the room after
74 TRANSACTIONS I. E. S. — PART 1
reflection from the ceiling and walls. The most common trend
in the color of walls and ceiling is toward cream, yellow, brown,
etc., that is, toward the "warmer" colors. I have shown in a
previous paper (Trans. I. E. S., Feb., 1913) that only an appar-
ently slight tint in wall coverings is sufficient to convert the
tungsten light by reflection to a quality even more yellow than
that of the carbon lamp light. Amber glass has not appeared
satisfactory to me owing to the greenish tinge. I have therefore
been experimenting for some time with the hope of producing a
proper yellow for converting tungsten light into the quality of
the light from a carbon lamp and yet enjoying the efficiency of
the former.
I have made many experiments with colored lights in the
home. These have ranged from deep amber to the lighter yel-
lows, rose, artificial daylight, etc. While I believe the results
are largely a matter of personal taste, I will state as my opinion
that an unsaturated yellow color is the most pleasing to me and
appeared to be a welcome change from daylight where daylight
color-values are not essential.
In the matter of the den mentioned in the paper I would state
that I believe it is well to avoid the use of too dark walls so com-
monly found in dens. I have found by experiment that in read-
ing under a well-designed table lamp and facing a dark wall that
I suffered very noticeable eye-fatigue in a short time.
I agree with a previous speaker that the dome is a satisfactory
fixture when well designed. However, it is possible to get prac-
tically the same lighting effect from showers. Take a shower
with deep narrow bell-shaped shades equipped with bowl-frosted
tungsten lamps. Direct light is sent downward upon the table
and light of any color depending upon the color of the shade is
diffused about the room. By this method the table is the bright-
est object in the room. I believe this should be the case and
therefore do not recommend so-called semi-indirect lighting in
the dining room. I believe there is nothing more important in
promoting sociability than the semi-darkness pressing in on a
group surrounding the table.
I am sure that we agree that Mr. Cassidy's paper is very
timely. In his last paragraph he sums up the situation very well
ART AND SCIENCE IN HOME LIGHTING 75
in the statement that he has tried in his paper to add the scienti-
fic element to that of the esthetic in the lighting of a moderate-
priced house and to show how one modifies the other. I think
this is highly commendable and suggest that we all must realize
that the fixture man can well reciprocate our efforts to enlighten
him in bringing home to us an extremely important phase of
lighting — the esthetic.
Mr. L. C. Porter: A great many of us are living in homes
already equipped with fixtures, which are not so attractive as
those shown here. Some very simple changes will frequently
make large improvements in many of the fixtures found in mod-
erate-priced houses and apartments. In the kitchen, for example,
there is frequently a single one-light fixture in the center of the
room. The use of a socket with a separable attaching plug will
allow a drop-lamp to be run over to the table or other place
where food is prepared ; this is a great convenience and will per-
mit the use of an electric flat iron and similar equipment at night.
Many dining rooms are equipped with domes, having bracket
arm showers around the center dome. It is a very simple matter
to give these brackets a half turn, pointing them towards the
ceiling, and install a io-watt all-frosted tungsten lamp in each
bracket. This will produce a low intensity semi-indirect illum-
ination over the entire dining room. If, in addition to this, an
efficient reflector equipped with a 6o-watt tungsten lamp is fast-
ened in the dome itself, directing a strong intensity of light onto
the table top, excellent dining room lighting will result ; i. e., low
general illumination throughout the entire room with strong light
on the table, making the table and those sitting around it most
conspicuous in the room.
The question of amber light is probably one of individual taste.
Personally, I do not care for it in a dining room, because it causes
the linen on the table to appear more or less yellow, giving it a
somewhat faded out appearance; whereas a strong white light
makes it appear fresh and clean.
In the living room many table lamps at present in use can be
improved by the use of lamps which are amber dipped on the
upper half, thus giving a pleasing color to the shade itself, and
at the same time throwing white light downward for reading.
/6 TRANSACTIONS I. E. S. PART I
Fixtures having a sort of hollow brass shell, from which showers
are hung, are often found in these rooms. It is a simple matter
to place in the top of this brass shell a ioo-watt tungsten lamp
in an efficient reflector pointed towards the ceiling and connected
with a drop-cord to the nearest shower socket. If the bowl of
the ioo-watt lamp is amber-dipped, semi-indirect lighting will be
obtained. Very nearly the same results can be obtained by paint-
ing the inside of the brass shell white, instead of placing the re-
flector there.
It frequently happens that in the bedroom there are candle-
sticks of one type or another, which it is not difficult to wire and
connect by a drop-cord from the top of the bureau to the nearest
lamp socket. A little 15-watt all-frosted tungsten candle lamp in
these candlesticks, one placed on each side of the mirror, makes
a useful ornament for a dresser.
The thought, therefore, which I wish to leave with you is that
considerable improvement can be made in the average fixture
at very little expense, and that it is good policy for the electric
light representative to assist the small purchaser — who does not
feel that he can afford the more elaborate fixtures — to make such
changes, thereby obtaining the confidence of one who some day
may be a large customer.
Mr. G. L. Hunter: During the past few years, this Society
has changed its point of view greatly. Several years ago when I
read my first paper here, on the subject of "Light and Color in
Decoration," many of you thought I wandered far afield because
I ventured to take up problems that had not previously been even
suggested. I ventured to say even then that white light for resi-
dence lighting is not desirable. I ventured to say that there are
many different kinds of daylight ; that as the environment
changes, the daylight changes. Daylight reflected from the sands
of the seashore is one thing; from the blue depths of the ocean,
another; from green forests and green grass, another; from
brown loam, or gray sagebrush, another; from red brick build-
ings, or white marble buildings, another. As the clouds overhead
change, as the color of the skies changes, the color of the daylight
changes. The color of the daylight also depends upon the hour
of the day. At early dawn when the sun first arises, it is glorious
ART AND SCIENCE IN HOME LIGHTING J 7
with red. As the sun ascends through the sky, the color of the
light changes from red through golden yellow to pure white at
noon.
Naturally, the constant discussion of color here to-night has
delighted me, for it was precisely what I had hoped to provoke.
I felt that until color was the first subject discussed in residence
lighting, and to some extent in all illumination, you were wasting
most of your effort; that your ideals as well as your practise
were wrong. The discussion here to-night makes it clear that
color is now foremost in the minds of those of you who are
attempting to improve the lighting of residences.
Mr. Cassidy has certainly presented a very interesting paper.
He has not only made many useful suggestions, but has arrived
at a number of valuable conclusions. But I did notice one sen-
tence in his paper to which I take the strongest exception. This
sentence is "So most homes to-day have lighting fixtures which
are esthetically correct." That I emphatically deny. I should
say on the contrary that, most homes to-day have lighting
fixtures that from the esthetic point of view are abominable.
They are ugly in proportion ; and incorrect in detail from the
point of view of historic style.
Personally I must admit that I am prejudiced in favor of
amber light. I know that amber light is softer on the eyes than
white light, and that most persons can see better with the light
that comes from the middle of the spectrum — I mean with light
that is not red and not blue. The effect of amber light can easily
be tested by everyone for himself, either under daylight or under
artificial light, by looking through a sheet of amber gelatin.
Both interiors and exteriors will be made softer and more agree-
able to the eye. Many clashes of color that exist in rugs or drap-
eries or wallpapers will be overpowered. Discords that by white
light are accentuated will by amber light be eliminated. Even the
extreme whiteness of the gas arc light can be agreeably dom-
inated by the use of amber shades. Some years ago I equipped,
with amber-and-gold leaded-glass shades, the wall brackets at
each end of a room 30 ft. x 16 ft. The shades were sufficiently
large so that there was no danger of their being melted apart by
the heat, and there was little direct light sent up or down. The
6
78 TRANSACTIONS 1. K.. S. — I'ART I
diffusion was largely of amber light in a horizontal direction, or
nearly so, illuminating brilliantly the walls of the room from _»
to 8 ft. high. I do not think I ever saw any room more agree-
ably lighted than this, or less expensively either. There was
absolutely no glare, and all the light that reached the eye had
been so transformed by the amber and gold opalescent glass of
the shades as to be grateful rather than offensive to the eye.
Of course the decorator will always keep in mind, and others
always should keep in mind, the fact that light is colored quite
as much by reflection as by refraction ; that it can be colored not
only by the glass bulb of the lamp, and by the glass or paper or
silk shade that surrounds it, but also by the walls or furniture
that reflect it. The decorator knows that when he colors the
walls of a room, he is at the same time coloring the light. If the
room is finished in soft tones the reflected light will be soft no
matter if it originates from tungsten-filament lamps. If the
walls be a muddy white the light will be a muddy light, no matter
if it start as a golden yellow.
One thing the decorator will be able to tell the illuminating
engineer with regard to amber light, is that it is safer to use.
decoratively, than any other light. White light makes a room
hard and unsympathetic. Blue light makes the blues of a room
cheerful, but makes the reds muddy looking. Red light brings
up the reds of a room, but makes the blues sombre and the
greens impossible. Amber light alone is sympathetic to all the
other colors, eliminating from an interior just enough of the
extreme reds and the extreme blues to produce harmony.
Mr. H. Thurston Owens: It is apparent that the ideas
which Mr. Hunter brought to the attention of this Society were
of great value but the reason they did not receive the attention
they deserved was due to the commercial propaganda of con-
siderable influence which was at its height at that time. The
commercial propaganda of to-day instead of being at variance
with the dictates of art is in accord with them.
Mr. G. H. Sticknky: While there are minor points in which
my ideas differ from those of the author, 1 am in agreement with
his general thought.
It is not surprising that, on account of our different relations
ART AND SCIENCE IN HOME LIGHTING 79
to the problem and our different antecedents we should have
different ideas and should each hold our individual ideas as super
ior to those of others. So long as there are so many installations
which are neither artistic, comfortable nor economical, there is
certainly much to be accomplished, and I believe the discussion
of a paper such as this helps toward the end of bettering the
practise.
The architect, decorator and fixture man handle the problem of
home lighting in advance. The central station and lamp manu-
facturer often attain their closest relation after the installation
is in operation, and frequently encounter dissatisfaction, due to
appearance, glare, and most often cost of operation. In seeking
to secure the best results we meet limitations due to the location
of outlets and style of fixtures and glassware. We are inclined
at times to blame the designers, though we realize that in many
cases they have been unable to express their own ideas on account
of the limitations of cost and taste imposed by the client. We do
feel that in many cases adherence to historical precedents has
prevented designers from adapting their practise to the modern
illuminants and other practical modern conditions.
Sometimes in the past we have undoubtedly erred toward the
other extreme of placing too much weight on economy of oper-
ation or efficiency, as measured in candlepower or foot-candles.
On the other hand, I believe that the illuminating engineers,
including those employed by the lighting companies and lamp
manufacturers, have done more to prevent this class of mistakes
than almost any other influence.
A progressive manufacturer is anxious to insure the best pos-
sible service from his apparatus, and likewise, the central station
is desirous of securing the most satisfactory use of current.
They have, therefore, employed illuminating engineers to make
a special study of lighting problems to educate and advise light
users and those interested in the design of lighting installations.
I believe this has done much to prevent undesirable extremes.
Much that the artistic designer blames the illuminating engineer
for is really done by untrained light users and others, without
the advice of the illuminating engineer, in seeking to better un-
satisfactory conditions. In such a case it frequently happens that
80 TRANSACTIONS I. E. S. — PART I
the light user turns to the opposite extreme, and I have always
felt that this result was somewhat the fault of the artist.
Perhaps I can illustrate my thought better by reference to a
typical experience in connection with the lighting of a fine hotel
in a western city. I was called in because the consumption of
energy required by the architect's plan seemed excessive. I
found that he was using a considerable number of beautiful
fixtures, employing numerous round bulb, frosted carbon incan-
descent lamps of low power. The effect and design was un-
questionably attractive, although it seemed to be unnecessarily
extravagant. I had the opportunity of calling the architect's
attention to a similar installation he had designed. Although
this had been in service less than a year the management had
substituted higher power, bare tungsten filament lamps in pear-
shaped bulbs, for the round bulb lamps which had been pre-
scribed. As can be imagined the effect was both inartistic and
glaring. After the architect had failed to persuade the manage-
ment to return to the original lighting, it was not difficult to
convince him to abandon this type of fixture and design one for
the new installation which would be both artistic and effective
with clear tungsten filament lamps. Through his ingenuity he
discovered that it was possible to make such fixtures which satis-
fied his artistic ideas even with due regard to precedent; and
he himself was protected, as far as his reputation was concerned,
from having his artistic work spoiled by those responsible for its
operation.
While, technically, architects or fixture designers may not be
responsible for the liberties which may be taken with the fixtures
which they design, the fact remains that the public does blame
them, and it seems to me there is some justice in this wherever
it is possible for them to avoid the condition likely to produce
these results.
Going back to the cost question : I agree that the home is one
of the last places where cost of lighting should be the deciding
consideration. It does not seem, however, practicable to entirely
ignore this factor ; in fact, it sometimes seems to me that the
lighting in the fine mansion of the wealthy man is even more
liable to be marred in search of economy than in the middle-class
ART AND SCIENCE IN HOME LIGHTING 8l
home. I have in mind a number of specific instances of this sort
which have come to my personal attention.
It is for the best interest of all of us that we should learn to
respect the truth in each other's view points.
Mr. G. W. Cassidy (In reply) : Referring to Mr. Powell's
discussion of my statement, "Instead of the soft yellow light of
the carbon lamp, one must now content with the hard, cold, white
light of the tungsten lamp," I wish to say that I referred to
the color of the light and not to its physiological effects or glare.
Regarding the statement, "Too little attention has been paid to
the color of the light," Mr. Powell adds that this condition is
being remedied by the illuminating engineer. No doubt this is
true of the few cases where the lighting expert is engaged to
design the installations of moderate-priced residences.
I have used an amber color in fixtures to bring out the decor-
ative effect of a room, and because it is a more or less neutral
tone.
Mr. Hunter takes exceptions to my statement, "Most homes
to-day have lighting fixtures which are esthetically correct." I
meant that most of the fixtures for residences have been designed
simply from the artistic side without regard to the scientific. I
agree with him that many of the results in evidence to-day could
hardly be called esthetic.
82 TRANSACTIONS I. K. S. — PART 1
AN ANALYSIS OF REQUIREMENTS FOR MODERN-
STREET CAR LIGHTING.*
BY L. C. DOANE.
Synopsis: In outlining the requirements of modern street car light-
ing, the author discusses elimination of eyestrain, maintenance, effect of
dust on efficiency of reflectors, efficiency of various lighting units, spacing
of outlets, wiring, etc. Tables giving cost and lighting data are appended
to the paper.
INTRODUCTION.
The first paragraph in the "Code of Principles" adopted by
the American Electric Railway Association at Atlantic City,
October 14, 1914, reads as follows :
The first obligation of a public utilities engaged in transportation is
service to the public. The first essential of service is safety. Quality of
service must primarily depend upon the money received in fares. For
this reason, it is necessary that the rate of fare should be sufficient to
permit the companies to meet the reasonable demands of patrons and to
yield a fair return on a fair capitalization.
This sums up very concisely the attitude of the public utilities
towards service rendered the public. They wish to give every
service possible, consistent with economical operation, but they
must be sure that any new demands of their patrons are reason-
able and that a fair return on their investment is forthcoming.
When it is known that 224,000,000 passengers were carried
in Pittsburgh last year in electric street cars; over 1,500,000,000
passengers in New York ; and over 500,000,000 passengers in Phil-
adelphia; and more than 40 per cent, of this travel was during
hours of darkness, artificial lighting stands out as a basic service
that must be rendered by the public utilities. The extent to
which this artificial lighting fulfills its duty is the determining
factor in regard to the quality of the service.
*A paper read at a meeting of the Pittsburgh Section of the Illuminating Engi-
neering Society, November 20, 1914.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
DOANE: MODERN STREET CAR LIGHTING 83
It is the object of this paper to determine what constitutes
good lighting and to show that good lighting is an asset to the
public utilities from the standpoint of returns on the investment
and service to the public.
GENERAL.
The artificial lighting of street cars, in order to be satisfactory,
must be acceptable both to the public and the public utilities. An
analysis of the requirements to be met, from the standpoint of
each interest, shows approximately the following results — as-
suming that the illuminating engineer is the representative of the
public.
REQUIREMENTS.
Public Utilities: 1. Economy of operation; 2. Economy of
installation; 3. Safety for passengers; 4. Ease of handling
passengers ; 5. Advertising value.
Public: 1. Sufficient light; 2. Elimination of eyestrain; 3.
Pleasing appearance.
Economy of Operation : Economy of operation depends on
the following items: (a) Cost of maintenance; (b) Cost of
power; (c) Efficiency of lighting units.
Each of these items will be discussed separately later in the
paper.
Economy of Installation. — The following items determine the
economy of installation of a lighting system: (a) Wiring; (b)
Spacing of outlets; (c) Cost of lighting units. Each of these
items will be discussed separately later on.
Safety for passengers; Ease of handling passengers; Adver-
tising value. — Each of these requirements will be met to the full-
est extent only when the following conditions are fulfilled: (a)
Sufficient light; (b) Elimination of eyestrain; (c) Pleasing
appearance.
Sufficient Light: An illumination of 1.5 foot-candles is the
minimum intensity consistent with acceptable lighting.1 Figuring
1 Ferree and Rand : Efficiency of the Eye Under Different Systems of Illumination ;
Postoffice Department Specifications for the Construction of Full Postal Cars ; A. R. E. E.
Report on Day Coach Lighting Tests.
84 rRANSACTIONS I. E. S. — PART I
on the basis that the voltage of the lamps often drops to 85 per
cent, of normal, which is equivalent to 55 per cent, of normal
light, and that a drop in efficiency due to dust on the lighting units
will easily amount to 15 per cent., the lighting system should be
designed to produce an average illumination of at least 3.75 foot-
candles at normal voltage at the plane of illumination. The
plane of illumination is usually taken 34 in. (86.36 cm.) above
the floor, the elevation at which the average reader holds a paper.
Elimination of Eyestrain: Eyestrain may be caused by in-
sufficient light, heavy shadows, uneven illumination, points of
high intrinsic brilliancy in the field of vision, or marked con-
trasts in illumination to which the eye must adapt itself.
To eliminate eyestrain, it is necessary to remove the causes of
eyestrain. The chief causes of strain are, bare lamps with fila-
ments of high intrinsic brilliancy placed in the field of vision,
insufficient light, and extreme contrasts.
No lamps should be used except with some form of shield
which will cover the bright light source to such an extent as to
entirely cut off the view of the brilliant filament from the or-
dinary field of vision. This shield may be either in the form of
a reflector or an indirect bowl.
An indirect lighting system in a street car is so expensive to
operate that it will not be considered further in this paper. Ex-
perience has proven it an unwise method to adopt at the present
time in spite of its merit in reducing eyestrain and eye fatigue.
A reflector, in order to be satisfactory as a shield, must extend
well down over the lamp. The approximate screening angle re-
quired has been determined by a series of tests conducted by
Air. A. J. Sweet. These tests were conducted to determine the
variation of eye efficiency with angle of light entering the eye,
and were made by directing a beam of light into the eye and
making a determination of what the eye could see under this con-
dition. The first determination was made with the beam directly
in line with the eye and then successive determinations were
made while the angle at which the light entered the eye was grad-
ually changed. It was found that the eye reached its normal ef-
ficiency when the beam of light entered at angles greater than 20
DOANE: MODERN STREET CAR LIGHTING
85
to 24 deg. from the direct line of sight. A graphical summary
of the test results is shown in Fig. 1.
It is interesting to know that Mr. Sweet has just completed an
exhaustive test for the Wisconsin Commission along similar lines
3 10 II 11 16 18 10 U iq
DEGREES FROM LlflEOF VISION
Fig. i.-Variation of eye efficiency with angle of light in the eye.
to his previous tests and that his original results have been cor-
roborated.
Two striking examples of the importance attached to the angle
of cut-off of a reflector are the specifying by the Post Office
kfeMzMzMzMz
W®
Fig. 2.-Diagram showing angles at which light from different units enters th
passengers. (Light at an angle of less than 20° is that which produces glare and eve
fatigue.)
Department of an angle of cut-off of not less than 20 deg. from
the horizontal on reflectors used for postal car lighting; and the
standard specification adopted recently by the Association of
86
TRANSACTIONS I. E. S. PART I
Railway Electrical Engineers, calling for an angle of cut-oft not
less than 25 deg. from the horizontal on all reflectors for car
lighting.
Fig. 2 shows the angles at which a passenger may receive light
from the lighting units in a car. In the case shown by this figure,
unit No. 6 has the most injurious effect. Units Nos. 4 and 5 a
lesser effect and units Nos. 2 and 3 practically no effect. With
bare lamps light enters the eye from each of these units, but by
the use of proper reflectors, it is possible to cut off the light from
all the units which are so located as to have a harmful effect.
Fig. 3. — Angle of cut-off 56-watt lamp with prismatic reflector, licavy
opal reflector, and light opal reflector.
Fig. 3 shows how it is possible to cut off the light above certain
angles. The reflectors designated as prismatic and heavy opal
have angles of cut-off of 18 deg. and 20 deg. respectively. These
two reflectors cut off practically all the harmful light. It might be
well to have a slightly greater cut-off, but this could only be ob-
tained at a considerable sacrifice in efficiency. The reflector
designated as light density opal does not give a sufficient angk-
of cut-off and should be changed in this respect before it will
fully perform its duty.
Extremes of contrast in intensities may. to a great extent, be
avoided by the proper distribution of light upon the plane of
f" US' ;15' nf ,«o" rti* l»S- ISS" «**" '•>*"
Fig. S.— Distribution of light ftom a 5t>-watt lamp with prismatic reflector, heavy
opal reflector, light opal reflector.
UUANK: MODERN STREET CAR LIGHTING &7
illumination and by using a light colored finish on the interior of
the car. The interior finish should be unglazed, for a glazed
surface would give unpleasant specular reflection.
Appearance : The appearance of a lighting installation gov-
erns to a considerable extent its success. An installation that is
unsightly or depressing is never a good one, be the engineering
results what they may. Opaque reflectors produce a depressing
effect due to the gloomy appearance of the upper part of the
car in comparison with the lower part. This fact eliminates them
from consideration.
The unsightliness of an installation depends to a certain extent,
on personal preference. Certain translucent reflectors may be
very pleasing to some people while to others they may be rather
unpleasant. This condition cannot be avoided. It is safe to
say that any translucent reflector — with the exception of a few
which, by selective absorption of the transmitted light appear
unpleasant in color — will be about equally acceptable to the aver-
age public.
Figs. 4 and 5 show two car lighting installations that are in
service.
Cost of Maintenance. — The cost of maintenance of an installa-
tion is a question of great interest to the public utilities. Here
is an expense that starts immediately upon placing a car in ser-
vice and continues during the life of the car. It is of vital im-
portance that this cost be kept as low as possible, if the greatest
returns on the investment are to be obtained.
Maintenance of any magnitude comes down to two items, these
being lamp replacements and reflector cleaning.
The life of all lamps is practically the same. The question
of the proper lamp for economical maintenance, therefore, comes
down to the question of cost of lamps and number of lamps.
Only tungsten lamps will be considered, as carbon and Gem
lamps are uneconomical in other respects than that of main-
tenance. (See discussion under Efficiency of Lighting Units.)
The 23-watt and 36-watt tungsten lamps cost exactly the same,
say three units. The 56-watt lamp costs four units and the
94-watt lamp costs 7 units. It requires J.3 units worth of
23-watt lamps, 4.7 units worth of 36-watt lamps and 4.2 units
88
TRANSACTIONS I. E. S. PART I
worth of 94-watt lamps for the same amount of light as is given
by 4 units worth of 56-watt lamps. This means that for equal
light, maintenance considerations point to the 56-watt lamp as the
most economical, the 23-watt lamp being 82 per cent, more ex-
pensive, the 36-watt lamp 17 per cent, more expensive and the
94-watt lamp 5 per cent, more expensive.
The cost of cleaning reflectors depends upon the number of
reflectors and the length of time before the reflector requires
cleaning.
The number of reflectors depends on the size of lamp and the
efficiency of the reflector. A full discussion of these 2 points
100
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Fig. 9. — Effect of dust on efficiency of reflectors.
is given under the headings of Spacing of Outlets and Efficiency
of Lighting Units.
The length of time before the reflector requires cleaning de-
pends on the rapidity with which efficiency drops off due to ac-
cumulation of dust, and to appearance.
Fig. 9 shows graphically the effect of dust on the efficiency
of three types of reflectors. This test was made by the engineering
department of the National Lamp Works to determine the rela-
tive merits of reflectors for factory service, but the results are
equally applicable to car lighting if only relative values are used.
From this figure, it is seen that the efficiency of heavy density
D0ANE: MODERN STREET CAR LIGHTING 89
opal reflectors is least affected by dust accumulation. Prismatic
reflectors come next and light density opal reflectors last.
Cost of Power.— Electric power costs the public utilities money,
whether it be bought or generated in their own plants. Every
additional kilowatt of energy used means an additional invest-
ment in generating units, distribution and feeder lines, and in
sub-station equipment. Public utilities are constantly expanding
adding more cars, extending their lines, requiring more power.
The argument that an economy of power is not a real economy
seems hardly justified under these circumstances. The day of
the public service commission and the elimination of all needless
expense is here, and it is such items as economy of power that
are going to lead to the highest economic efficiency. A study of
the discussion on Costs will throw some interesting light on this
subject.
Efficiency of Lighting Units.— Under the heading Sufficient
Light it has already been stated that there is a minimum intensity
for satisfactory lighting. It is also true that the most efficient
method of obtaining this intensity will require the least amount
of energy.
Table I shows the average efficiency of various lighting units
as obtained by a series of tests which is described later under the
heading Tests.
TABLE I.— Efficiency of Various Lighting Units.
Wting unit Efficiency ^
Bare carbon lamp g <-
Bare tungsten lamp 22 x g
Light density opal reflector 35 , 0
Medium density opal reflector 40 3>5
Heavy density opal reflector 45 40
Clear prismatic reflector S4 . g
The reason for the increase in efficiency with the use of tung-
sten lamps and reflectors is first, that the tungsten lamp generates
light practically 3 times as efficiently as does the carbon lamp
and second, that reflectors will so redirect the light of the tung-
sten lamp as to make much more of it useful in lighting the bot-
tom of the car instead of the top. Fig. 8 illustrates very effectively
the way in which the light of the bare tungsten lamp is redirected
down onto the seats by various reflectors.
90 TRANSACTIONS I. K. S. — PART 1
Wiring. — There are four methods of wiring which are in gen-
eral use for car lighting. These are as follows : i . Exposed
wiring between roof and headlining; 2. Conduit wiring between
roof and headlining; 3. Open conduit wiring on ceiling; 4.
Open conduit wiring on roof.
The first two methods are probably best for wiring new cars
or wiring old cars while they are shopped for general overhaul-
ing. The latter two methods are the most economical for chang-
ing over an old car, and are necessary when there is a very small
clearance between the headlining and roof.
Local conditions will have to determine which method of wir-
ing is most economical, until such time as street car designs are
standardized.
Spacing of Outlets. — Spacing of outlets depends on the ef-
ficiency of the lighting unit, the distribution of light by the light-
ing unit, and the seating arrangement of the car.
The Association of Railway Electrical Engineers in its report
on "Day Coach Lighting Tests" finds that a spacing of 6 ft. to
7 ft. 6 in. (1.82 to 2.28 m.) between units should not be ex-
ceeded, as greater spacing produces uneven lighting and ob-
jectionable shadows. They also found that there was no ad-
vantage to be gained by using two rows of lighting units instead
of one, but this may be modified in street car lighting practise.
It is quite probable that two rows of units reduce shadows in
street cars having longitudinal seats, although the increased cost
of installation and maintenance for such a system is very likely
to offset any gain in illumination that may be made.
By calculations from the results of the tests on the efficiency
of various lighting units, it is possible to determine the maximum
allowable spacing for any units. The results of these calculations
are given in Tables II and III.
TABLE II. — Maximum Ai.i.owaki.k Spacing of Units.
Half -Deck System. Two Rows of Units.
Size of lamp
Reflector 23-w 36-w 56-w 94-w
None 2 ft. 6 in. 4 ft. 3 in. 6 ft. o in.
Light density opal 4 ft. 9 in.
Medium density opal... 5ft. gin.
Heavy density opal 6 ft. 6 in.
Prismatic clear 7 ft. o in.
DOANE: MODERN STREET CAR LIGHTING 91
TABLE III.— Maximum Allowable Spacing of Units.
Center-Deck System. One Row of Units.
Size of lamp
Reflector 23-w 36- w 56-w 94-w
None 1 ft. 3 in. 2 ft. o in. 3 ft. o in. 5 ft. 6 in.
Light density opal 2 ft. 6 in. 3 ft. 9 in. 5 ft. 9 in. 7 ft. 6 in.
Medium density opal ... 2 ft. 9 in. 4 ft- 6 in. 6 ft. 6 in.
Heavy density opal 3 ft. 3 in. 5 ft. 0 in. 7 ft. o in.
Prismatic clear 3 ft. 9 in. 5 ft. 9 in. 7 ft. 6 in.
Cost of Lighting Units.— The cost of lighting units depends
upon the cost of holders, lamps and reflectors.
Holders for the various sizes of lamps are all the same and
therefore the fewer the units required, the lower is the cost for
holders.
It has already been shown that for equal amount of light the
56-watt lamp is most economical.
Reflectors vary in cost according to the glass that goes into
them and the cost of the molds in which they are made. It is a
peculiar fact that the lower the efficiency of a reflector the lower
is its cost. An investigation of the discussion on Costs will, how-
ever, show that though the individual reflectors may vary in cost,
the increased efficiency of the more expensive ones permits the
use of a fewer number, which brings them all down to practically
the same plan.
The selection of lighting units, therefore, should be made on
the basis of maintenance cost and economy of operation, rather
than on the cost of the lighting unit itself.
Tests. — A majority of the various comparative tests conducted
to determine the efficiency of an installation, have been made on
only two or three types of reflectors and these often the wrong
size or type for the sen-ice. It has also been the practise to use
uncalibrated lamps, inaccurately calibrated instruments and
fluctuating voltage. Under such circumstances the probability of
rather serious errors is introduced.
During the last part of May, 1914, an illumination test embody-
ing twelve different installations was made on one of the double-
truck closed cars operated by the Indianapolis Traction & Ter-
minal Company. Every precaution was taken to make the re-
92 TRANSACTIONS I. E. S. — PART I
suits accurate and conclusive. The car in question measured
7 ft. 6 in. (2.28 m.) wide by 32 ft. 6 in. (9.9 m.) long inside.
Photometric readings were taken on a test plane 34 in. (86.3
cm.) from the floor, at twenty stations 30 in. (76.2 cm.) apart,
each on one of three position lines, one intersecting the position
/nsta//atian A/oi fastat/ation Afa 2.
• -64 Wo/t Cardan lamps, Sore •-£3-We/f Tungsbm Lamps, Bare
-*— — # * % $ %—■
Iitstoi/otion A/o.3
• S6 h/att JunasTtn L* m/w> Jtare.
®-J& Mf/^TunjSTtJi Uoi-mpiw/tn tieory density opa/ rvfiectors.
/nstat/atibn A/o 4
• -£3'H/attTunottm kamp*,0<"*
• -23-/ro#TunoSTt» Lamps, *///> tiyht density opa/ ref/ectors.
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%
fnstet/ation A/o. 5
• -23 WottTunytTn, L<rmpi,Bare.
<g)-23 Wot/Tun^Sten LampspitA c/ear prismatic rs//ectors.
Sl-fh H/ottTutijitin Lampt,^i/h e/eor prismatic re/iectors.
Kig. ii. — Arrangement of lighting units.
of passengers seated next to side windows, another intersecting
the position of passengers seated next to the aisle, the third coin-
cident with the longitudinal center line of car.
All instruments were calibrated in the laboratories of the Na-
tional Lamp Works immediately prior to the tests. All lamps
DOANE: MODERN STREET CAR LIGHTING
93
were rated — with the exception of the 64-watt carbon lamps and
23-watt tungsten lamps — and the exact amount of light obtained
from each of them was known. All voltages were held constant
by means of rheostats and greatest accuracy was used in making
the readings. At the end of every third or fourth test, a check
reading was made on the bare lamps to see that no changes had
occurred either in the output of the lamps or in the reading of
the instruments.
Table IV gives a summary of the results of these tests, and
lists all items of importance.
COSTS.
In order to form an idea of the comparative costs of lighting
with various installations, the figures shown in Tables V, VI
and VII have been prepared.
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Kig. 12.— Length of time required for installations to pay for themselves.
Five typical installations have been figured.
Fig. 11 shows the arrangement of the five installations.
Table V shows the cost of power and maintenance.
Table VI shows the investment.
Table VII compares the various installations with respect to
cost of power and maintenance, and amount of investment.
Fig. 12 shows in graphical form the length of time required
for each installation to pav for itself, both when replacing carbon
7
94 TRANSACTIONS I. E. S. — PART I
lamps that have already been installed and when making an
installation in new cars.
CONCLUSIONS.
The intention of this paper is to present what data there is
available on street car lighting and allied subjects before you in
such form that each one may draw his own conclusions.
doane: modern street car lighting
APPENDIX.
95
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DOANE: MODERN STREET CAR LIGHTING
97
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MODERN STREET CAR LIGHTING 99
DISCUSSION.
Mr. S. G. Hibben : The fittings used here were developed
specially for this high voltage service. The voltage across the
base terminals of a lamp, in case of a burn-out or an open cir-
cuit, would be momentarily the full line voltage of 1,200; there-
fore, the space separating the contact points was increased from
8/ia to about 3/s in., or in other words a mogul base was neces-
sary, instead of the standard Edison base, to safe-guard against
arcing over. This large base in turn necessitated a special shape
of lamp bulb and the use of a shade with a fitter larger than the
standard 2>4 in. size. A metal holder is manufactured to prop-
erly cover the outlet box (all the wiring on high-voltage circuits
should preferably be in metal conduit) and this holder takes a
white glass shade with a 3% m- fitter.
Sometime ago it was debated whether, on account of possible
breakage due to inertia of the shade and sudden stopping and
starting of cars, it would not be better to standardize a 2^4 m-
or a 334 m- fitter for the usual installation. However, the results
so far have indicated that no trouble is to be found when using
a shade with the regular 2]/^ in. fitter. Of course, it is assumed
that this refers to only those properly made shades which are
carefully annealed.
There is on the market a metal holder for shades with 2^4 m
fitters, for which prismatic or white glass shades are available,
either with or without a lip.
If any operating companies find that they lose a considerable
number of lamps by theft, they may prevent this through the
use of a lamp receptacle in which the lamp screws into a closely
coiled spring wire. This wire acts as a screw thread, allowing
the lamp base to be inserted easily, but fastens it when one at-
tempts to unscrew the lamp. Pressing out the coiled wire by a
screw-driver blade or similar tool allows the lamp to be removed.
The author presents exact data on the angles at which glare is
found, but shows results of some experimentations that is diffi-
cult to perform, and rather uncertain to generalize upon. As to
angles of cut-off in shades of various depths, it is a matter of
considerable difference of opinion as to how deep a shade must
be. Other tests might lead to different results.
10O TRANSACTIONS I. E. S. — PART I
Obviously, also, any shade through which the light is not soft-
ened will not be satisfactory, whatever its depth and its large
angle of cut-off.
Judging from observation of open-bottom shades of various
depths, I would always advocate using bowl- frosted lamps with
94- watt units, and in some cases on other sizes as well.
Fig. 7 gives interesting data, but would be more nearly ap-
plicable to car lighting if one could know what were the con-
ditions of test. The shapes of reflectors, the surroundings and
other items all enter into and influence such results.
The cleaning cost for any shade installation, I believe, will
usually be found to be greater than that given in Table V. at
least in Pittsburgh.
Mr. G. \Y. Roosa: Reflectors should be cleaned as often as
the car windows ; but I imagine that in general practise this is not
done since dirt on shades and lamps is not so apparent. Many
operators do not realize the amount of the loss of light due to
dirt.
IVES: PHYSICAL PHOTOMETRY IOI
PHYSICAL PHOTOMETRY.*
BY HERBERT E. IVES.
Synopsis: This paper deals with the question of substituting some
physical instrument for the eye in photometry. The nature of light as a
measurable physical quantity, the defects of the eye as a measuring instru-
ment and the desirable qualities of a physical photometer are reviewed.
Next the various means which have been suggested are examined, among
these selenium, the photo-electric cell and the photographic plate. A new
thermo-couple artificial eye is described, with an account of its perform-
ance as a laboratory normal eye for colored light photometry.
INTRODUCTION.
It is perhaps not unsafe to say that the great majority of those
who have photometric observations to make in the course of
their daily work have at one time or another been attracted, or
even fascinated, by the idea of finding some substitute for the
eye, some instrument to make light measurement more like other
kinds of measurement to which we are accustomed. Whether the
object sought is greater sensibility, simplification of apparatus,
greater ease in reading, or the production of an artificial normal
eye to help solve the heterochromatic photometry difficulty, the
panacea recurrently brought forward is the physical photometer.
As is usually the case when the same idea arises spontaneously
in many minds, there is a real field— or rather fields— for devices
to take the place of the eye. But, as is frequently the case with
a popular idea, there have been many premature and ill-consid-
ered attempts to use this or that medium sensitive to light,
attempts based on insufficient or faulty analysis of the real
requirements. Much misdirected work might have been saved or
made useful had it been preceded by a very careful study of the
real weaknesses of visual photometry.
The present paper is an attempt at a thorough analysis of the
light measurement problem from the standpoint of a possible
purely objective means of solution. This analysis must start at
the basis of photometric science with the query : What is light ?
It must then study the eye as a measuring instrument; it must
establish criteria to which an artificial eye must conform. Fol-
* A paper read at a meeting of the Philadelphia Section of the Illuminating Entri
neering Society, November 7. 1914. g B,ug
. The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
102 TRANSACTIONS I. K. S. PART I
lowing this, a review will be made of the various promising
instruments and methods for physical photometry, noting how
closely they approach the criteria established. From this study
it is hoped to show what forms of physical photometers are even
now available for some kinds of work, and what we may look
forward to in the near future.
WHAT IS LIGHT?
Steering clear of what has appeared to be a stumbling block
to some, let us at once clearly distinguish between the sensation
of light, which is purely subjective, and the usual cause of that
sensation, namely, radiant energy of certain qualities. It is with
this latter alone that we have to do at the present time in pho-
tometry. Starting then, without further discussion, with the fact
that light is to be identified with radiant energy, the most impor-
tant question demanding answer is how to differentiate light
from other forms of radiant energy. The physicist has usually
been content to accept Lord Kelvin's dictum that "if you can see
it, it is light." Such a conception of the nature of light, perhaps
more than anything else, is responsible for the encumbering of
our physical journals and texts with values of so-called "luminous
efficiencies," which indicate only in the crudest approximation
the relative light-giving efficiencies of illuminants. Any useful,
exact, quantitative evaluation of radiation as light demands a
better considered definition than this. Such a definition is that
officially adopted by the Illuminating Engineering Society,
namely, that "luminous flux is radiant power evaluated according
to its capacity to produce the sensation of light." This defini-
tion tells us at once what weight is to be attached not alone to
invisible radiations, such as those beyond the violet, but to that
inefficient radiation at the ends of the visible spectrum which has
furnished so large a share of the "visible" energy in the luminous
efficiency determinations to which reference has been made.1 It
presupposes the existence of a definite determinable evaluating
factor, the stimulus coefficient or luminous efficiency, upon which
more will be said in discussing the eye.
Enough has here been said on the nature of light to make clear
the backbone of all schemes for physical photometry, namely, the
1 Ives, H. E.. luminous Efficiency; Trans. I. E. S.. vol. V., p. 113.
IVES: PHYSICAL PHOTOMETRY IO3
measurement of radiation. We shall see, however, that the
further refinement of making the proper evaluation as light is
not necessary for all the purposes for which the physical pho-
tometer has been desired.
THE EYE AS A MEASURING INSTRUMENT.
There are in general two types of measuring instruments, those
which indicate by the actual magnitude of their response, and
those which indicate the equality or lack of equality of two com-
pared stimuli. The first of these types is well illustrated by the
common switchboard ammeters and voltmeters, from which the
current or voltage is read off directly by the position of a pointer
on a scale. The second type, sometimes called "null" instru-
ments, is illustrated by the potentiometer with its sensitive gal-
vanometer used to detect the condition of no potential. In gen-
eral the null type of instrument can be made to yield greater
sensibility, but this must be paid for by greater complexity of
apparatus.
The eye belongs in the class of null instruments. It is common
knowledge that one can make only the crudest estimate of candle-
power by looking at a light, no matter what one's previous experi-
ence. Nor is it possible to estimate with any degree of accuracy
how much brighter one light or illuminated surface is than
another alongside. What the eye can do, and do very well, is to
decide when two adjacent surfaces are equally bright. That is,
the eye can take the place of the galvanometer in a potentiometer.
Just as the latter tells when there is no difference of potential
applied to its two sides, so the eye tells when there is no differ-
ence of brightness. Just as in the potentiometer we get at our
measure of relative potentials by knowledge of the conditions of
resistance and the value of the voltage standard, so in photom-
etry we arrive at our result by knowing the distances between
lamps and screens, the value of the standard and the transmis-
sions of various auxiliaries.
When so used the sensibility of the eye to small differences is
quite high. Differences of the order of magnitude of y2 per
cent, are sufficient to register as inequality. This degree of sen-
sibility is probably quite sufficient for present technical needs.
io4
TRANSACTIONS I. E. S. PART I
For scientific purposes, cases might of course arise where greater
sensibility would be advantageous.
So far nothing has been said about color, or more properly,
color differences. As long as the two lights under comparison
are of the same color a condition of equality can be decided upon.
But if the lights are different in color the one condition under
which the eye has a high degree of precision is lost.
The relative apparent brightness of two adjacent colored sur-
faces is, with an individual eye, a function of the illumination, of
the size of the surface, of the surroundings, of the past history
of the observer. It may be determined with more or less pre-
cision and with varying results by different photometric methods.
u
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a
jb
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A
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Fig. i.— Relative luminous efficiencies of the various spectral radiations. (Average normal
spectral luminosity curve of eighteen observers for an equal energy spectrum.)
I f another eye is used a different result may be obtained. Hence
it is that the evaluation of radiant power "according to its
capacity to produce the sensation of light" is not a simple matter.
It is my belief, however, that as a result of a thorough study of
photometric methods in relation to color, evaluation factors can
be determined applicable to the great majority of practical cases.
Such a set of evaluating factors constitute a spectrum luminosity
curve of the average eye. Such a curve is shown in Fig. I." It
will be assumed in what follows, without further discussion, that
the question of color in physical photometry is completely cov-
- Ives, H. E., The Luminosity Curve of the Average Eye; Phil. Mag., Dec, 1912.
IVES: PHYSICAL PHOTOMETRY 105
ered by the common adoption of a definite luminosity curve or
luminous efficiency curve of the spectrum.
WHAT IS SOUGHT IN AN ARTIFICIAL EYE?
The various goals sought in physical photometry owe their
origin to dissatisfaction with one or another of the limitations of
the eye just discussed. They should be listed and discussed
separately, as will now be done, although various combinations
of desirability and feasibility will be found, which will make any
classification merely of temporary aid. A helpful preliminary
division is into the cases where there is no color difference and
vice versa.
A. Where there is no color difference — (i) Indication by posi-
tion rather than by quality. Probably one of the most insistent
demands for the physical photometer has its root in the desire
to avoid the consideration of quality, substituting for it the esti-
mation of position. Thus while the eye can detect a difference
of brightness of J/2 per cent, it is probably almost universally
true that observers practised and unpractised much prefer to
have this difference indicated by the movement of a pointer over
a scale. There are several reasons for this. For one thing the
great majority of our measuring instruments are of this type. I
know of but one instrument where a quantity which could be
measured by a moving pointer is indicated by the intensity of
illumination, and in this case it is done because the other factor
in the comparison cannot readily be shown by positional indica-
tions.3 For another thing most of our measuring instruments
have a comparatively enormous store of power to draw upon,
so that the problem of getting large deflections is the least to be
faced. As we shall see later, the condition is far different with
light measurement. Again, the eye is probably working at higher
efnciency in estimating the position of a pointer than in esti-
mating equality of brightness, for quality discrimination is at its
best with the black pointer and divisions on a light background.
and binocular vision and the possibility of movement render our
determination of position very exact. At any rate this desire for
positional indication rules no matter whether readings are to be
made by null method or by proportional indication.
3 Ives, H. E., A New Form of Watts Per Candle Meter; Electrical World, June 8, 1912.
106 TRANSACTIONS I. E. S. — PART I
(2) Proportional indication. A very common demand made
of a physical photometer is that it shall indicate luminous intensity
by the magnitude of the deflections of a pointer. In short, that
we may by this means be freed from the limitations of the null
method, for which the eye is alone capable. A great advantage
of this over the null method lies in the consequent simplification
of apparatus. It enables us to dispense with the comparison
lamp, with the moving carriage and, in fact, with the whole pho-
tometer track.
(3) High sensibility. Two kinds of sensibility must be distin-
guished. First is what may be called total sensibility measured
by the amount of light which may be detected. Thus, as we
know, the eye can see under illuminations extending all the way
from thousands of meter-candles down to thousandths. Our
chief interest in sensibility in a physical photometer at present
is to obtain even that total sensibility necessary to measure ordi-
nary working illuminations of the order of 10 meter-candles.
The second kind of sensibility is the capacity to detect small
differences. It has already been stated that the present attainable
differential sensibility with visual photometry is high enough for
most practical purposes. This sensibility is, however, the limit we
may expect, unless some new principle like the contrast principle of
the Lummer-Brodhun should be found. If higher sensibility is
ever necessary it must be sought in the physical photometer, to
which there is apparently no inherent limitation to sensibility,
whatever may be the present practical limitations. Such greater
sensibility might, however, be purchased only at the price of
simplicity; the null method would probably be necessary, leaving
as the only advance over the eye (apart from the greater sensi-
bility) indication by position.
(4) Simple method of response. Where there is no question
of the use of color filters to alter the wave-length sensibility of
the sensitive surface the advantage of some simple mode of
response, such as response directly proportional to stimulus, is
exactly on a par with that in any measuring device. Perhaps
the most desirable scale would be one giving the same increment
of deflection for the same percentage change of stimulus in all
the most used parts of the scale (Fechner's law). The most gen-
erally useful scale is one giving directly proportional deflections.
IVES : PHYSICAL PHOTOMETRY IO7
(5) Constancy. A physical photometer whose indications were
absolutely constant from time to time would be the acme of
desirability. Especially is this desirable if its indications are not
according to some simple law. In this case the labor of recali-
brating after change would be very difficult. If, on the other
hand, some simple law is followed, constancy over long periods
of time is not absolutely essential. Frequent checking with a
standard is too common a procedure in exact measurement to be
a serious drawback.
(6) Recording capacity. In line with the modern wide use of
recording instruments, we may note that a recording photometer
would have much the same reasons for use in technical light
measurement as recording pyrometers have in heat or tempera-
ture measurements.
(7) Integrating capacity. A photometer which could store up
its impressions would have certain uses. For instance it would
simplify the measuring of fluctuating light sources such as cer-
tain arc lamps. It would as well offer possibilities in measuring
the quantity of light delivered, in distinction to gas or electrical
energy, for which the public service company now has to charge,
thereby shouldering all the cost of increased efficiency in lighting
means.
(8) Practicability. Various paramount considerations with
respect to total sensibility and to convenience may be grouped
under "practicability." Thus every desirable feature so far men-
tioned would be of no immediate practical value if the physical
photometer could be operated only in a specially built laboratory
and under certain weather conditions. All sensitive apparatus is
necessarily delicate, and it therefore becomes necessary to know
whether the physical photometer is to be feasible only in the
standardizing laboratory, or in the industrial laboratory, or in the
field, and what its limitations will be in each case.
B. Where there is color difference. — To the desirable qualities
which have just been enumerated must be added another which is
indispensable if lights of different colors are to be compared.
The sensitive medium must be affected by the different wave-
length radiations of the spectrum in exactly the same relative
amounts as the average eye. The extreme unlikelihood of any
io8
TRANSACTIONS I. E. S. PART I
sensitive substance possessing this distribution of sensibility as
found lends emphasis to the necessity of a quality already men-
tioned. The relation between stimulus and response must be of
a simple character, preferably it should be rectilinear. Unless
this is the case it is not possible to alter the wave-length sensi-
bility curve by the use of absorbing media or equivalent means.
This requirement must be met no matter whether the indications
are to be by a pointer over a graduated scale or by the null
method.
INSTRUMENTS USED TO MEASURE RADIATION.
A detailed description of the instruments available for measur-
ing radiation will not be attempted here, as such descriptions are
to be found in the standard physical text books and journals.
Fig. 2.— Bolometer. The resistance of the thin platinum grid, P, is altered when it
receives radiation, thus disturbing the balance of the Wheatstone bridge.
The salient points of each are exhibited in the Figs. 2 to 7 with
their attendant legends. Our chief interest here is in classifying
and appraising them for photometric needs.
These instruments can be divided on two bases — the basis of
sensitiveness, i. e., the quantity of radiation they can measure, and
the basis of their behavior to various qualities of radiation, or
selectivity, as it is called. For instance, a black bulb thermom-
eter is equally sensitive to all kinds of radiation, visible or in-
visible, but it takes a very large amount of radiation to produce
respectable indications. On the other hand the photographic
plate is chiefly sensitive to blue, violet and ultra-violet light, but
it is so sensitive that instantaneous photography is a common-
IVES: PHYSICAL PHOTOMETRY
109
place. It may be noted in passing that there appears to be no
exception to the general rule, of which these cases are examples,
that great total sensitiveness is obtainable only at the cost of
limited spectrum range of sensibility. The eye, with its range of
only a single octave of the lengthy scale from X-rays to wireless,
is another notable example of this fact.
The chief non-selective radiometers are the bolometer, the
thermopile, the radiometer and the radiomicrometer. The first
of these, made famous by the researches of Langley, consists es-
sentially of a fine strip of blackened platinum whose electrical
resistance is altered with any change in its temperature. Radia-
tion falling on the strip heats it and causes a change of resistance,
Fig. 3.— Simple thermopile. The unequal heating of the hot and cold
junctions causes an electric current to flow.
which is indicated by a sufficiently sensitive galvanometer con-
nected to the Wheatstone bridge system, of which the platinum
strip is one element.
The thermopile consists of one or more junctions of dissimilar
metals or alloys selected as having a large thermo-electric power.
When the junctions are heated by radiation the electromotive
force produced is sufficient to drive a small current through a
galvanometer connected in series with them. Both of these in-
struments, it will be noted, necessitate a galvanometer as auxiliary.
no
TRANSACTIONS I. E. S. PART I
Their sensibility and practicability are to a large degree condi-
tioned by this limitation. The two remaining instruments of this
group are simpler in this respect, being complete in themselves.
The radiometer, developed by E. F. Nichols from the toy de-
vised by Crooks, consists of a light double vane suspended in a
partial vacuum. One side of each vane is blackened and when
radiation falls on one of these blackened faces the vane is rotated,
its motion being shown by the reflection of a spot of light by a
small mirror carried on the suspending fiber.
Pig. 1. — Radiometer. The radiation falls on a light vane, blackened on one
side, in an evacuated enclosure which is rotated on its support.
The Boys radiomicrometer is practically a thermo-junction be-
tween the poles of a magnet. When a current flows through the
thermo-junction circuit, due to its heating, the coil of wire to
which the junction is attached turns in the magnetic field, its
motion being indicated by a beam of light from an attached
mirror.
Coming now to selective radiometers, the chief of these are the
selenium cell, the photo-electric cell and the photographic plate.
IVES: PHYSICAL PHOTOMETRY
III
Of these, selenium has perhaps secured the greatest notoriety.
The applicability of this remarkable element is due to its property
of changing its electrical resistance under the action of light.
Consequently when connected in series with a source of electro-
motive force and a sensitive galvanometer, the illumination or
obscurement of the sensitive surface is detectable.
The photo-electric cell, in particular when constructed from one
Fig. 5.— Radioniicronieter. The radiation falls on a thermo-junction which is carried on
a small coil of wire. The coil lies between the poles of a magnet, and when radiation
on the thermopile causes a current to flow, the coil rotates.
of the alkali metals, is one of the most interesting and lately most
studied possibilities in this line. In brief, an alkali metal surface,
preferably in a vacuum or partial vacuum, when illuminated gives
off negative electricity. When connected with an electrometer
or a sensitive galvanometer (there are several different methods
of arranging the apparatus) a current flows upon the illumination
of the surface. The last of these selective physical photometers
112
TRANSACTIONS I. E. S. — PART I
to be mentioned here is the photographic plate, which is the best
known example of chemical change produced by light. From our
standpoint the photographic plate is a means of recording the
amount of incident light by the amount of deposited silver. It is
quite distinct from all the preceding means considered in that it
requires nothing in the way of an auxiliary galvanometer or con-
ditions of extreme freedom from vibration.
These three instruments just considered have been grouped
Fig. 6.— Selenium cell and connections. L, light source ; S.shutter ; C,
selenium ; D, battery ; G, galvanometer.
'HHHHF-/
Fig. 7.— Connections for photo-electric cell. B, battery ; C, cell ;
G, galvanometer ; E, earth.
together for the reason that they are not, in their natural condition,
equally sensitive to all qualities of radiation. Thus the selenium
cell, speaking roughly, is sensitive chiefly to radiations near the
visible. The photo-electric cell, of sodium, potassium, rubidium
or caesium, is chiefly sensitive in the ultra-violet, but increasing
toward the visible region in the order given. The photographic
plate is normally most sensitive to the blue, violet and ultra-
violet. By means of sensitizers however it may be made sensi-
tive as far as the deep red.
IVES: PHYSICAL PHOTOMETRY II3
DISCUSSION OF THESE INSTRUMENTS AS PHYSICAL
PHOTOMETERS.
It will now be our task to discuss each of these instruments
with reference to the desirable qualities previously outlined. From
this discussion one may hope to determine in what lines of work
physical photometry is apt to be of practical value now or in the
near future.
At this point it becomes necessary to study the quantity of
radiation involved in what we have decided to call light, in par-
ticular reference to the sensibility of the instruments we have
been considering. For some reasons it would be preferable to
reduce all the quantities involved to absolute units, but we may
for our present purpose save much time by utilizing the fortunate
fact that the sensibility of radiometric instruments is usually ex-
pressed in terms of the effect produced by a candle at a meter's
distance — our own familiar meter-candle. Thus it is found that,
using the most sensitive instrument yet constructed of the class
of the bolometer, radiometer and thermopile, a deflection of 50
centimeters per square millimeter of sensitive area is of the order
of magnitude obtainable.
Now the most recent determination of the luminous efficiency
of the 4-watt electric lamp is 0.45 per cent. Consequently a 16
candlepower lamp at a meter distance, which gives no inconsid-
erable illumination, would, if measured through a proper light-
evaluating screen, give only 4 millimeters deflection. And this
is under the most refined laboratory conditions, with the most
perfect freedom from mechanical disturbance, and from changes
in the temperature of the surroundings. Reference to Fig. 8,
where the total radiated energy, and the energy evaluated as light
are shown, tells the same story. These illustrations bring us at
once to the most serious problem in physical photometry. The
amount of energy available as light is of excessive smallness.
This difficulty can be met and is being met in various ways. In
some of the instruments the exposed area may be made greater
than one square millimeter; means are being studied to increase
the intrinsic sensitiveness, such as evacuating the surrounding
space; greater freedom from the effects of changes in the local
temperature is obtained by instruments of the compensated type;
1 14 TRANSACTIONS I. E. S. — PART I
and every year brings improvements in the sensibility and rug-
gedness of sensitive galvanometers and other auxiliaries. How
far we have progressed in this direction is shown below, where
actual practical examples are given wherever practicable.
A. The Non-Selective Instruments. — The bolometer, radio-
meter, radiomicrometer and thermopile may be treated in practi-
cally the same description. First, the case where there is no
question of color difference; for instance the measurement of
two electric incandescent lamps of identical color. These instru-
3.5 4.0 45
Fig. 8. — Ratio of luminous flux to radiant power in the carbon lamp.
Small area, luminous flux.
ments possess the simplest mode of response, that is, their indi-
cation is directly proportional to the intensity of the incident
radiation. They therefore lend themselves to the problem of
reducing our measurements to a positional basis and in that way
to simplification of apparatus. Their practicability depends
chiefly on the amount of radiant energy available. Since there
is no question of color difference, we frequently meet with the
possibility of utilizing a large amount of invisible energy to help
out. Thus with the two incandescent lamps we are considering
if we measure the total energy instead of simply the visible we
have at least ioo times as much at our command, and this means
the difference between delicate laboratory conditions and the or-
dinary photometer room. Whether this opens up a really valu-
able possibility or not depends on whether the light and the total
energy are always proportional in the two supposedly similar
IVES: PHYSICAL PHOTOMETRY 115
light sources. In many cases this is true. A practical example of
a promising field for the utilization of total energy measurements
to secure positional indications is the reading of gas flame candle-
powers. So much energy is here available that with a string
galvanometer and a large area surface thermopile it should be
possible not only to read but automatically to register candle-
powers by the photographic registration of a moving spot of
light or similar sensitive method.
A considerable degree of constancy is to be expected in the
readings of these instruments, sufficient at least so that checking
with a standard at occasional intervals during a series of meas-
urements would be sufficient. The possibility of securing greater
differential sensibility than with visual photometry is not to be
anticipated, particularly where one is compelled to use the in-
visible energy to obtain workable deflections.
But so few and of so little importance are the cases where we
work with lights of exactly the same quality that the slender
possibility we have just considered is of little more than aca-
demic interest. This is shown by the fact that practically all the
recorded attempts to use these radiometers in photometry have
involved some scheme for approximating the luminosity curve
of the eye.
Turning, then, to the case of photometry with a color differ-
ence, we find that the first difficulty with the non-selective radiom-
eters is that they are not sensitive to radiation as is the eye,
but to the whole scale. This has two consequences, first, that
some means must be adopted to alter the wave-length sensibility
and, second, as already pointed out, that when this alteration is
made, the remaining sensibility is extremely small.
However, since these instruments possess the simplest mode
of response, it is feasible to alter their distribution of sensibility,
and the fact is that at the present time the only truly satisfactory
physical photometer is of this type. Before describing this in-
strument, recently developed in the United Gas Improvement
Company's physical laboratory, historical mention should be
made of earlier instruments of the same type.
Fery,4 in 1908, constructed and used a radiomicrometer over
* Bull. Soc. Frauc de Physique, 1908, p. 148.
Il6 TRANSACTIONS I. E. S. — PART I
which was placed an absorbing solution of copper acetate to ob-
struct the infra-red radiation and to cut down the "visible"
roughly in proportion to its luminous efficiency. This instru-
ment though crude was on the right principle and proved the
feasibility of the scheme. It was used quite extensively by Fery
in his studies of the power relations in the incandescent lamp.
In 191 1 Houston,5 in connection with his proposal for a primary
standard of light, described a combination of two solutions —
copper sulphate and potassium dichromate — which give a close
approximation to the best determination at that time of the
luminosity curve of the spectrum. These solutions used with a
radiometer constitute a physical photometer calculated for lights
of any color. Recently Dr. Karrer, at my suggestion, worked out
Fig. 9. — Thermopile artificial eye. L,, light source ; S, shutter ; E, luminosity
curve solution ; T, thermopile ; G, galvanometer.
a combination of three solutions in separate tanks, whose total
transmission is very closely the luminosity curve of the spectrum
according to the latest determinations. This solution has been
used to make determinations of true luminous efficiencies, but is
immediately applicable to photometry.
Benefitting by this previous work I have recently been able to
develop a visual luminosity medium, complete in one solution,
approximating practically perfectly to the luminosity curve as
previously determined by him. This has been set up in front of
a sensitive surface thermopile, thereby making an artificial eye
exactly corresponding to the real normal eye under the adopted
standard photometric conditions (Fig. 9) and indicating position-
ally by the relative deflections of a pointer.
Now, all attempts hitherto made in this direction have labored
6 Proc. Royal Society A, 191 1, p. 275.
IVES: PHYSICAL PHOTOMETRY 117
under the great disadvantage that there has been no means of
determining whether the instrument's readings were right. The
convenience and precision of the former devices was generally
recognized, but whether their readings actually corresponded to
the true ones could not be established, because no standard method
of colored light photometry had been developed; nor were there
any standard reproducible colors that had been measured by any
photometric method. Recently in a paper6 before this society a
colored absorbing solution of very useful qualities was described,
together with complete measurements by the method of colored
light photometry developed by the writer. With these various
means at hand it has been possible to bring this problem to a
definite and successful conclusion. We have carried through
with our physical photometer the same measurements made vis-
ually with the result shown in Fig. 10. The agreement is so per-
fect that we are now using the physical photometer directly in
those cases where the solutions had already made possible enor-
mous simplification of work. We now use this device to calibrate
incandescent lamps of any color and for the standardizing of
colored glasses for use in visual photometery to eliminate color
differences in practical work. We are by this means enabled to
secure accurate and satisfactory results in a few minutes which
previously required the cooperation of a large number of obser-
vers and several days work.
The limitations of this device are those already enlarged upon,
namely, it is strictly a laboratory instrument. It is operated in
a basement as free as possible from vibration and large tempera-
ture changes. It must be used with rather high candlepower
sources as close as possible to the receiving surface. But these
are not serious limitations at all from the standpoint of those
standardizing laboratories in whose hands will rest the calibra-
tion of color difference eliminating media. It is to the solution
of this important problem that we offer this completely developed
physical photometer.
B. The selective instruments. Of the selective instruments the
first to claim attention is the selenium cell. This has attracted
a great deal of attention and justly so, for it actually rivals the
6 Ives, H. E., and E- F., Kingsbury, Experiments with Colored Absorbing Solutions
for Use in Heterochromatic Photometry; Trans. I. E. S., vol. IX, No. 8.
n8
TRANSACTIONS I. K. S. PART I
eye in sensitiveness. That is, it makes possible the translation of
illuminations within the range to which the eye is accustomed,
into movements of a pointer of a magnitude easily appreciated.
By so doing, as already pointed out, not only is photometric
reading made easier but half of the photometer bar or its equiva-
lent may be dispensed with.
Fig. 10.
10 0 10
CONCENTRATION. PER CENT
-Comparative results, visual and physical photometers.
40
The error of many who have tried to use the selenium cell is
in their assumption that this is all that is needed to fit a physical
photometer for the attack of any problem. We may quickly
differentiate between the use and abuse of the selenium cell by
reference to the various qualifications previously enumerated.
IVES: PHYSICAL PHOTOMETRY
119
On the standpoint of sensibility and practicability it ranks high.
Thus it is possible with a cell of large area, using dry cells as
source of e. m. f., to obtain satisfactory readings, on a portable
millivoltmeter, of ordinary artificial illuminations. These are
defects in the way of inertia, changing sensibility and the like,
which, however, can be largely met by a fixed procedure in
exposing and by mounting the selenium in an evacuated space.
Going at once to the question of behavior toward light of
different colors, a very peculiar and interesting state of affairs is
found. The wave-length sensibility curve of selenium is not the
800
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o
200
100
400.
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HI
TI
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Fig. 11.— Wave length sensibility curves of selenium for various
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same as that of the eye. This alone is not fatal, provided the
substance is sensitive to all visible radiations, as selenium is, for
a sensibility curve may be altered as was shown in the case of
the radiometers. It is questionable whether any two selenium
surfaces will be apt to have exactly the same distribution of sen-
sibility through the spectrum, which is a serious drawback, as it
would make each cell an individual problem to manufacture
properly screened. But more serious than this is the fact that
the method of response is different for different colors. For
I20 TRANSACTIONS I. E. S. — PART I
most of the visible and ultra-violet spectrum the response is as the
square root of the stimulus, while for the deep red it is directly
as the stimulus.7 As a consequence any absorbing medium or
equivalent means for producing a desired distribution of sensi-
bility through the spectrum is rendered worthless. This is
clearly shown by the wave-length sensibility curves for different
intensities of illumination exhibited in Fig. n. While an absorb-
ing medium could be provided to take care of either of these
methods of response, nothing will take care of both.
What then is the field for selenium in photometry ? This : the
measurement of radiation of definite fixed quality upon which the
apparatus has previously been calibrated. As long as the ap-
paratus is used throughout on this same radiation all is well, but
immediately lights of different quality are to be measured and
selenium is of no value to us, no matter how great its sensibility or
convenience. Selenium is now being used successfully in scientific
investigations where monochromatic light must be evaluated under
conditions where the much less sensitive radiometers would be
out of the question. It could be used to measure artificial il-
luminations with great advantage over visual photometers. But
if so used it would, after being calibrated on a carbon lamp,
measure only carbon lamps correctly.
Our discussion of the next selective instrument — the photo-
electric cell — may be considerably shortened by reason of the
fullness with which the previous instruments have been treated.
The photo-electric cell containing one of the alkali metals lies
between the non-selective radiometers and selenium in its total
sensibility. Connected with the proper sensitive auxiliaries, it
has been found sensitive enough to detect the illumination from
a single match yards away. A cell of large area of the most
sensitive type will record daylight illuminations on a portable
galvanometer, and with a voltage supply of 50 to 100, which can
be made portable, artificial illuminants can be at least detected.
The photo-electric cell has attracted much attention of late because
it has been thought that its indications are directly as the inten-
sity of the incident illumination. It has been thought, too. that
since its color sensibility extends into the visible spectrum, it
7 Pfund, A. H.. The Use and Abuse of the Selenium Cell in Photometry; Lighting
Journal, 1913.
IVES : PHYSICAL PHOTOMETRY
121
should be possible to apply absorbing media, as in the case of the
thermopile artificial eye but with greatly increased sensibility. In
fact Dr. Voege has recently described experiments with such an
apparatus. All these hopes were fated to be blasted, for the
present at least, by recent work which has shown that the response
to light is not directly as the intensity, but is a complicated func-
tion of several factors, and is as yet quite uncontrollable.8 The
illumination-current relationship for a number of cells is shown
in Fig. 12.
A still further objection to the photo-electric cell is that the
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Fig. 12. — Illumination-current relationship in various photo-electric cells.
wave-length sensibility does not appear to be the same from one
cell to another,9 a point exhibited in Fig. 13. Another point
exhibited by the latter figure is that the maximum sensibility of
these cells lies far out in the violet of the spectrum. Conse-
quently the amount of available energy after an appropriate ab-
sorbing medium has been introduced to make them read "light"
is quite small. The presence of these two defects in the photo-
electric cell must defer its consideration in this connection until
its properties have been much more thoroughly studied.
8 Ives, H. E., The Illumination-current Relationship in Potassium Photo-electric
Cells; Astrophysical Journal, June, 1914.
9 Ives, H. E., Wave-length Sensibility Curves of Potassium Photo-electric Cells:
Asirophy steal Journal, Sept., 1914.
122
TRANSACTIONS I. E. S. — PART I
The fact that neither the selenium cell nor the photo-electric
cell lend themselves to any method of copying the wave-length
sensibility curve of the eye makes it possible to subject them both
to the sweeping criticism that they do not measure light, as we
have defined it, at all. Under certain restricted conditions they
measure radiations which under those conditions are proportional
to light.
We now come to the last of the means for physical photometry
040 042 04+ 046 046 050 051 054 056 058 060 Q6t 064 069 QM
J*
Fig. 13.— Wave-length sensibility curves of various photo-electric cells,
reduced to equal energy spectrum.
that we shall consider, namely, the photographic plate. Perhaps
the most striking difference between it and the instruments we
have been considering is that in its use we definitely abandon any
attempt to secure direct positional indication. The photographic
record when obtained must itself be measured, and in this meas-
urement either the ordinary photometric methods or some radio-
metric scheme must be employed. It goes therefore almost with-
out saying that the photographic plate is not resorted to for con-
venience. In ordinarv photometry it would only introduce extra
IVES: PHYSICAL PHOTOMETRY
12}
work without any gain, unless the plate could be measured with
greater precision than could . the original illumination, which is
hardly likely. Resort to photography is then only to be expected
if there are some things the plate can do well enough to offset this
disadvantage.
The photographic plate has extreme sensibility, as alreadv
pointed out. It can be made sensitive to the visible spectrum as
shown in Fig. 14. Its response is, over a considerable range of
intensities, proportional to the stimulus.10 It presents thus far
no great advantage over the eye. Its most striking peculiarity is
that it can integrate, not only the effects of very faint stimuli but,
with some limitations, fluctuating or changing stimuli. This
ERYTH ROSIN
ETHYL RED
PINACHROM
DICYANIN
Fig. 14.— Sensibility of photographic plates sensitized and unsensitized.
to different regions of the spectrum.
property is chiefly taken advantage of in the measurement of
faint spectra, such as that of the fire-fly and in other cases where,
as above pointed out, the measurement is not really that of light
but radiation. Some use has however been made of photography
to measure as light the irregular distribution curves of arc lamps,
which because of the unsteady character of their light are dif-
ficult for ordinary photometry.
The photographic process is very sensitive to many disturbing
influences. To avoid the errors these influences may cause, it is
necessary to use careful substitution methods, and to adhere to
10 Ives, H. E., The Application of Photography to Photometry; Trans. I. E. S., vol
VII, p. 90.
124 TRANSACTIONS I. E. S. — PART I
very carefully worked out procedures in exposure and develop-
ment, all of which conspire to deprive the photographic methods
of photometry of precision, leaving their field restricted to cases
where photography will do something nothing else will.
SUMMARY.
In this paper an attempt has been made to clarify the question
of physical photometry, first by determining what it is we want
to measure ; second, by tabulating the qualities which would be
desirable in instruments to take the place of the eye. It has been
found that the various desirable qualities are found scattered
among a number of instruments, none of which possesses enough
to give it a claim to be a universal "light" measuring device. At
the present time only one instrument, the non-selective radio-
meter with a proper evaluating absorptive medium, does actu-
ally perform as an artificial eye. Its limitation is its comparative
insensitiveness, which restricts its use to the laboratory, where
however it has a field of great usefulness. For the much greater
sensitiveness of some of the devices to become available we must
look to future developments.
WHAT WE MAY EXPECT IN THE FUTURE.
The history of the measurement of radiant energy is a record
of continually increasing sensibility of instrumental means, fol-
lowed by the transfer of these more sensitive means from the
laboratory to the technical stage. Thus within a few years the
thermopile has been made much more sensitive by the use of
new substances for the thermo-electric junctions, by study of
the best dimensions, by new processes of evacuation. More and
more sensitive galvanometers have been built, and, what is more
to the point for the present purpose, increasing ruggedness and
practicability have been attained, especially in the string types of
galvanometer. In view of these facts it is not unreasonable to
hope that before very long the successful type of physical pho-
tometer which has been described here may be available for many
other than standardizing purposes.
On the side of the selective means a truly enormous amount of
work is being done. The photo-electric cell in particular, be-
IVES: PHYSICAL PHOTOMETRY I>5
cause of its bearing on many important points in physical theory,
is the object of wide study. The relation between illumination
and current, and the differences in wave-length sensibility in
various cells of the same composition, are subjects under study,
and with increased knowledge it is to be expected that we shall
acquire control of the disturbing factors. That accomplished, we
shall hope to utilize the enormous sensitiveness of this class of
instrument and at the same time make them measure light.
126 TRANSACTIONS I. K. S. — PART 1
AN APPROXIMATE UNIFORM PH( >T< METRIC
POINT-SOURCE.*
RY A. B. KENNKLLV, R. W. CHADBOURN AND G. I). EDWARDS.
Synopsis: Experiments are described on a modified form of frosted
tungsten ioo-watt spherical stereopticon lamp with a view to producing
a uniform virtual point-source. The measurements show that exempting
an axial cone, at each pole, of 45 deg. semi-angle, or 29.3 per cent, of the
total spherical area, the maximum deviation ratio of the lamp (the ratio
of the maximum deviation of the intensity to the mean spherical intensity
over the retained area) was 4.65 per cent.
A luminous point-source may be denned as a source of light
condensed in so small a volume as virtually to constitute a mere
point in space for the purposes under consideration. Such a
point-source would be specially serviceable for placing at the
focus of a parabolic reflector in the production of a parallel beam
of light. A point-source to serve for a projector does not need
to distribute light uniformly in all directions. It only needs to
radiate light from a central point.
In the theory of photometry, however, it is customary to start
with the simple concept of a uniform luminous "point-source,"
or an ideal lamp which distributes light uniformly in all direc-
tions, as though the source were concentrated at a single point.
No lamp can be produced to comply with such a concept. There
must always be an appreciable surface-area in the luminous
source, and this surface is seldom even approximately spherical.
It is supported by a more or less opaque structure, in a chamber
whose walls are not uniformly transparent; so that the distribu-
tion of luminous flux is frequently very far from being uniform
in different directions, even at long radial distances from the
lamp. At short radial distances from the lamp, the distribution
of light is apt to depart still further from uniformity. In actual
service, this departure from the condition of a simple uniform
luminous point-source is not of great consequence, except that
* A paper presented at a meeting of the New England Section of the IUumtnatinu
Engineering Society, November 10. 1914.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
KEN NELLV,CIIADBOURN, EDWARDS \ LUMINOUS POINT-SOURCE 12J
whereas from a photometric standpoint, a single measurement of
candlepower taken in any direction would completely specify a
uniform point-source, the ordinary non-uniform radiator requires
to have its candlepower measured in many directions, in order
adequately to specify its photometric properties. We also know
that for particular purposes in illumination, a marked departure
from uniform distribution may be desirable; as, for instance,
when a lamp is needed to emit a strong beam of light in a selected
direction.
Nevertheless, there would be a certain convenience in the pho-
tometer room, if a virtual uniform point-source were available;
i. e., a source which, although of appreciable dimensions, would
emit light uniformly in different directions and, under its condi-
tions of use, would act substantially as though this light emerged
from a point. Standard incandescent lamps are ordinarily cali-
brated for mean horizontal intensity when rotating, or for a con-
stant intensity in one geometrically defined direction, when fixed
with this direction along the axis of the photometer bar. A vir-
tual uniform point-source would make rotation unnecessary in the
first case, and the marking of the fiducial direction unnecessary
in the second case. Such a lamp would be easy to set up, and to
calibrate in a photometer. It could only be expected to serve as
a virtual point-source at a suitable photometric distance ; because
no light source can be produced at a mere point, and, at very
short ranges, actual luminous surfaces must be expected to depart
widely from point-source conditions.
A virtual point-source photometric standard would also have
the advantage that its mean spherical reduction-factor would be
unity, and its total flux of emitted light would be just 47r times
its intensity as measured in any direction. A rough criterion of
the degree of approximation offered by any lamp to a point-
source, is its spherical reduction factor with respect to 1.0. A
lamp with a spherical reduction factor differing materially from
1.0 must differ materially from a point-source at the photometric
distance considered. On the other hand, a lamp might have a
spherical reduction factor of 1.0, and yet might differ greatly
from a point-source. For example, it might happen to have a
mean horizontal candlepower just equal to its mean spherical
128 TRANSACTIONS I. E. S. — PART I
candlepower, and yet display considerable irregularity in candle-
power in different zones. A strict definition of deviation from
the point-source condition at a given radius of measurement
might be stated as the greatest difference between actual candle-
power in any direction and the mean spherical, divided by tin-
mean spherical candlepower. This might be called the point -
source deviation ratio of the lamp, for the radius of photometric
observation considered. If applied over the entire sphere, how-
ever, perhaps no existing lamp could possibly escape a large
deviation ratio ; because in the case, say of an incandescent lamp,
where the conducting wires entered the lamp, a shadow would
have to be cast, and the deviation from mean spherical candle-
power would have to be considerable along the direction of this
shadow. Nevertheless, the practical utility of the definition might
be fairly well maintained by expressing some reservation for the
shadow cone. Thus, if an incandescent lamp had a shadow near
its base comprised within a right cone of, say, 45 deg. semi-angle,
within the apex formed at the optical center of the lamp, as indi-
cated in Fig. 3, the mean spherical candlepower might be reck-
oned to the exclusion of this basal shadow zone. Over the rest
of the sphere, the deviation from the mean spherical candlepower
thus delimited might conceivably be reduced to insignificance at
distances beyond one meter. Such a lamp would be a virtual
uniform point-source at and beyond meter^distance, except within
the 45 deg. conical zone comprising the lamp-base. In general.
the ratio of point-source deviation for such lamps could be re-
duced by increasing the size of the exempted zone ; until, however,
the exemption became so large that the utility of the lamp as a
virtual point-source became seriously restricted. With an axial
cone of semi-angle 45 deg. as in Fig. 3, the exempted area would
be vers 45 deg. = 0.293 of the hemisphere surrounding the cone,
and with 45 deg. axial cone at each pole the exemption would be
0.293 of the whole sphere. That is, the retained area would be
0.707 of the whole sphere. Expressed in solid-angle measure,
the retained angle would be 0.707 X 4" steradians and the
exempted angle 0.293 X 4^ steradians. In general, with an axial
cone of semi-angle 6 exempted at each pole, the retained area
would be cos0, and the exempted area vers0 = 1 — cos0. taking
the whole area of the sphere as unit}-.
KEN NELLY, CHADBOURN, EDWARDS : LUMINOUS POINT-SOURCE 129
Several unsuccessful attempts were made by the writers to find
an existing type of lamp which might approximate a uniform
virtual point-source. The lamp department of the General Elec-
tric Company assisted us, however, by preparing a modification
of one of their tungsten ioo-watt stereopticon lamps of the spher-
ical frosted type with a concentrated spiral tungsten filament.
This type of lamp is illustrated in Fig. i. Its external diameter
Fig. i.— Diagram of a ioo-watt concentrated, tungsten-filament stereopticon
lamp 3% in. in diameter.
is 3.75 in. (9.53 cm.). The tungsten wire filament is first wound
in a spiral approximately 1 mm. in diameter. This spiral is then
looped up and down in a crown of 10 hook-supports indicated in
plan by Fig. 2. Two lamps of this type were tested, one with a
clear globe, and the other with a frosted globe. As might have
been expected, the clear-globe lamp was decidedly inferior to the
frosted-globe lamp as a uniform point-source; so that we need
only consider, in what follows, the results obtained with the
130
TRANSACTIONS I. E. S. — PART I
Fig. 2.— (Upper diagram) Plan of supported filament. Fig. 3.— (lower diagram) Axial
section of a tungsten-filament stereopticon lamp, indicating an exempted core at
each pole of semi-angle 450.
CANDLE POWER
ZO 40 A 60 F 80
Pig, 1. Rousseau diagram.
KENNELLY.CIIADBOURN, EDWARDS : LUMINOUS POINT-SOURCE 13 I
frosted lamp, the globe of which was uniformly and completely
frosted.
The lamp was set up in the photometer rotating about its axis
about 100 revolutions per minute. There was actually but little
candlepower difference in azimuth ; so that the test might have
been made without rotating the lamp, if the mean of several read-
ings in fixed azimuths at each zone had been taken.
The zonal distribution curve and the corresponding Rousseau
diagram are given in Fig. 4. It will be seen that the luminous
intensity remains fairly close to 75 candles over a considerable
solid angular range. Above an elevation of 60 deg., the intensity
falls off to 55.8 at the tip, apparently owing to reduced reflecting
power from the walls within the socket. Below a depression of
45 deg"., the intensity falls off rapidly, apparently owing to ab-
sorption of light by the hooks, and socket. Nevertheless, the
mean spherical candlepower comes out 70.5 with a mean hor-
izontal candlepower of 74.9, making a spherical reduction factor
of 0.941. It is evident that the curved line ABCDE on the
Rousseau diagram of a true virtual point-source would be straight
and parallel to the base O E.
The corresponding involute diagram is shown in Fig. 5.1 Here
the successive arcs are drawn in zones of 15 deg. The polar
diagram is indicated by the broken line 90 deg., 75 deg., 60 deg..
45 deg., 30 deg., 15 deg., o deg., —15 deg.. —30 deg., —45 deg..
— 60 deg., — 75 deg. The corresponding involute is ABCDE
FGHIJKL M. Half the total projected vertical distance be-
tween A and M measures 70.4 candlepower to scale and repre-
sents the mean spherical candlepower of the lamp, with a spher-
ical reduction-factor of '—-+ = 0.940. It is evident that for a
74-9
virtual point-source, the involute M L K — C D E F would be-
come a true semi-circle, and the evolute, or line of centers
PQRSTUVWX would shrink to a single central point at T.
If we consider the point-source deviation ratio of this lamp
after exempting a conical region of 45 deg. semi-angle with re-
1 Kennelly, A. E. A Rectilinear Graphical Construction of the Spherical Reduction
Factor of a Lamp ; Trans. I. E. S., February, 190S. A New Graphic Method for Deter-
mining the Mean Spherical Intensity of a Lamp by the Length of a Straight Line when
the Curve of Meridianal Intensity is Given. Electrical World, March 28. 1908.
I 32 TRANSACTION'S 1. K. S. PART I
spect to the axis; i.e.., retaining only the region from — 45 deg.
to -(-45 deg. of elevational angle, we find on the Rousseau dia-
gram that the mean spherical cp. is represented by the distance
h 1 1 or * I since the area i I H h is found to be equal to the planim-
etered area of the curve over the base ih. The mean spherical
cp. over this exempted area is 74.2. The greatest deviation from
Fig. 5.— Kennelly diagram.
this value over the retained area is at eD = 70.8 or 3.4 cp. The
maximum deviation ratio is thus — — — 0.0458 or 4.58 percent.
74.2
As already pointed out, the area retained is 70.7 per cent, of the
whole area of the sphere; or the exempted region is 29.3 per
cent. Over the entire retained area, the maximum deviation
from the mean retained spherical cp. is thus only about 4.5 per
cent.
KEN NELLY, CHADBOURN, EDWARDS: LUMINOUS POINT-SOURCK 1 33
Similarly, in the involute diagram of Fig. 5, retaining only the
involute curve D E F G H I J, the mean retained spherical candle-
. . di'..
power is half of the vertical distance D J or — divided by
0.707, or 74.3. The maximum deviation over this retained area
is 74.3 — 70.8 = 3.5 cp. and the maximum deviation ratio -^-
= 0.0471 or 4.71 per cent. If both the Rosseau and involute
diagrams could be drawn without any inaccuracies, their results
would, of course, be in agreement. In this case, the maximum
deviation ratio may be taken at the average value of 4.65 per
cent, over the retained area between +45 deg. and — 45 deg. It
is evident from either of the diagrams (Figs. 4 and 5) that be-
tween -{-30 deg. and — 30 deg. the deviation ratio would be much
less, but this would exempt half the area of the sphere.
If the frosted tungsten stereopticon lamp here considered were
further modified in structure, the approximation to a uniform
virtual point-source could evidently be increased. Thus, the
base of the lamp might be removed and replaced by a thin glass
tube, or pair of tubes, carrying out the leading wires. Again,
the globe might be enlarged, the spherical form continued over
the area covered by the present base, and the filament supporting
wires arranged for minimum shadow. With all of these amend-
ments, the exempted area might probably be considerably re-
duced, and the maximum deviation ratio also. Perhaps the max-
imum deviation ratio might be reduced to 2 per cent. It is hoped
that, as a matter of interest, it may be possible to carry on further
experiments in this direction.
TRANSACTIONS
OF THE
Illuminating Engineering Society
Vol. X NUMBER 2 1915
SOME USES OF LIGHT IN THE TREATMENT
OF DISEASE.*
BY E. C. TITUS, M. D.
Synopsis: The value of light as an efficient remedy when properly
employed in the treatment of many painful and diseased conditions is
discussed in the following paper. A brief review of the art of apply-
ing the therapeutic effect of light is also included.
To many the subject of phototherapy is invested with so much
mystery, and its fundamental principles are so frequently imper-
fectly understood, that it is not surprising that progress in this
field has been so slow. Even now comparatively few are making
systematic use of this important therapeutic agent. It would
consume much more time than is at my disposal to present more
than an outline of this subject, and I will therefore confine
myself chiefly to its practical therapeutic aspect, as based largely
upon my own observations.
From time immemorial the beneficial influence of sunlight upon
animal and vegetable life has been recognized, but it is only at
the present time that we are appreciating its full value in the
treatment of disease.
The excellent and even wonderful results of heliotherapy in
the treatment of bone tuberculosis, to which attention has been
called within a recent period, will serve as an illustration.
For obvious reasons, however, sunlight is not always avail-
able, and it has therefore been found advantageous to resort
to other sources of light. Thanks to the progress made in elec-
tricity, we now have at our disposal various means of obtaining
light closely approaching that of the sun in its remedial action,
and to these means, chiefly, my paper will be devoted.
* A paper read at the eighth annual convention of the Illuminating Engineering
Society, Cleveland, O., September 21-24, i9r4-
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
I36 TRANSACTIONS I. E. S. — PART I
Phototherapy may be considered under two heads, its thermic
and actinic effects, although both of these are represented in
varying degrees in all light, irrespective of its source.
It must be remembered that the thermic effects of light are
due to the impingement of the rays upon the translucent cuta-
neous tissues. The arrest of the light rays by the skin and sub-
cutaneous structures produces radiant heat which has a higher
penetrating power than convection heat as generated by a hot-
water bag or poultice, for instance. It has been found that the
thermic effects of light extend to a depth of two inches or more,
while convection heat is principally exerted upon the surface.
In comparing the therapeutic action of both it will be seen that
the changes produced in the tissues by the former are much
more pronounced. Thus if the body be exposed to an intense
light, as in an electric light cabinet bath, the resulting hyperemia
and elimination of waste products by the skin and kidneys (cel-
lular nutrition) are much more pronounced than in a Turkish
or Russian bath. The marked augmentation of the oxidation
processes in the tissues is shown by the greater amount of carbon
dioxid thrown off by the lungs and by the increase of solids in
the urine. It is also claimed that the natural defences of the
body (phagocytosis) are greatly promoted.
The actinic or chemical rays play an important part in photo-
therapy only when the light is concentrated upon a localized area
as in the use of the arc lamp. Under these circumstances the
actinic rays appear to enhance as well as modify the action of
the thermic and luminous rays. Thus the ultra-violet radiations,
which are actinic, have been shown to exert an anti-bacterial
action as well as to promote local phagocytosis.
I am not unmindful of the fact that much of our knowledge
is still in the theoretical stage, and for that reason have refrained
from entering into the many details. I will, therefore, proceed
now to the clinical aspects of this subject, dividing it into the
general and local applications of phototherapy.
The general application of phototherapy consists practically in
the use of the electric light bath, and since much of the benefit to
be derived from this agent will depend upon the apparatus
employed, I will first give a description of what has proven to
me to be the most satisfactory type of cabinet.
TITUS: EIGHT IN THE TREATMENT OF DISEASE 13/
An electric light cabinet should be constructed according to the
following plan. The cabinet should be octagonal in shape, 4 ft.
square by 5 ft. high; the lining should be of white blotter and
not mirror surface; the source of light should come from 100
40-watt tungsten lamps, conveniently arranged, so that they will
be under control from within by properly placed switches, one-
half or full number of the lamps to be employed, as desired.
The cabinet should be open at the top, not entirely, but partly
so and it should have an air vent 3 inches in diameter in the
center of the floor, over which is placed a low stool 18 inches
high, upon which the subject is seated. (It has been found that
a ventilated room is much more quickly and evenly heated arti-
ficially than one that is closed or sealed.) The further advan-
tages of this construction are that a large volume of light with
a minimum amount of heat is produced in the cabinet, that the
emanations of noxious gases and odors from the human body
are quickly carried off, that the degree of cutaneous hyperemia
and diaphoresis is much more intense, and that the usual de-
pression and other unpleasant symptoms are entirely obviated,
as compared with the older form of closed cabinet.
Among the conditions in which the electric light bath has
proved to be most serviceable are arteriosclerosis (hardening of
the arteries), gouty and rheumatic conditions, Bright's disease,
diabetes, obesity and acute catarrhal affections of the respiratorv
tract.
In the majority of cases of arteriosclerosis in the earlier stages
I have advised the regular use of these baths with beneficial
results, and I firmly believe that they have warded off more
serious organic changes which otherwise frequently ensue.
The effects of the baths are :
1. To induce intense hyperemia or reddening of the skin and
thus reduce the congestion of the deeper organs, which is fre-
quently present.
2. To increase elimination by way of the lungs and skin. It
has been found that during and following the bath the elimina-
tion of carbon dioxid is practically doubled, while the profuse
perspiration produced carries away much toxic or poisonous
material and in that way relieves the overtaxed kidneys. As it
is generally accepted that toxemia plays an important part in the
l$S TRANSACTIONS I. E. S. — PART I
causation of hardening of the arteries, the benefit to be derived
from this method is readily apparent.
Rheumatic and Gottty Affections. — In late years it has been
frequently pointed out that many conditions commonly termed
rheumatic differ essentially from the acute type of the disease
which is very probably of bacterial origin. On the other hand,
there is abundant reason to believe that these chronic forms
which have been grouped under the names of rheumatoid arthri-
tis, rheumatic gout, osteo-arthritis, arthritis deformans, are the
result of auto-intoxication and disturbances of metabolism.
From what has been said above it will be readily understood
that the marked effect of the electric light bath in increasing
elimination will exert a beneficial influence upon the toxemia in
these cases and therefore prove of material aid to other treatment.
The distressing pains and stiffness in the joints are also greatly
relieved as patients have frequently assured me. In chronic
gout, which is more frequent in this country than is generally
thought, the action of light baths is to augment the cutaneous or
peripheral circulation and in that way favor the absorption of
uratic or chalky deposits.
It may be asked why a Turkish or Russian bath will not do
equally well in the conditions mentioned. My own experience
has shown that the effect of the light bath is much more pro-
nounced and prolonged.
Bright's Disease. — One of the chief aims in the treatment of
Bright's disease is to lessen the work of the kidneys. The light
bath will be found a better auxiliary measure for accomplishing
this purpose than the usual hot pack or steam bath. As pre-
viously pointed out, notwithstanding the profuse sweating
induced, the patient experiences no depression because of the
stimulating effect of the light energy upon the peripheral nerves.
Diabetes. — The light baths are not adapted to every case of
this disease, but particularly to patients who present a dry skin
with various cutaneous eruptions, especially of an eczematous
character. The best results are obtained where diabetes is
attended with high blood pressure.
Obesity. — The heat penetration in an electric light bath, which
as already mentioned extends to a depth of over two inches, stimu-
TITUS: LIGHT IN THE TREATMENT OF DISEASE 1 39
lates the oxidation processes in the fatty tissues and promotes
their disintegration in cases of obesity. It will thus prove an
excellent auxiliary to the customary treatment.
Acute Catarrhal Affections of the Respiratory Tract. — The
writer has frequently had an opportunity to witness the beneficial
effects of an electric light bath at the beginning of a cold in
aborting it or greatly ameliorating its course. From personal
experiences there can be no question of its superiority over the
customary hot bath and diaphoretic (perspiration inducing)
remedies.
LOCAL APPLICATION OF LIGHT.
In the local applications of light the following means are
available :
i. The arc light, which is best employed by means of an ordi-
nary marine searchlight, with its glass front window removed.
The one I employ consumes 25 to 35 amperes of direct current
at 40 volts, and projects the light in parallel rays by means of a
12-inch parabolic reflector, and has a light value of about 5,000
candlepower.
2. The high power incandescent lamp with a carbon or tungsten
filament of 500 candlepower and provided with a dome reflector.
The carbon filament uses 12 amperes at no volts, while the
tungsten lamp consumes only 3 amperes at no volts. The
former gives off more thermic rays, while the latter produces a
greater amount of white light with a minimum amount of heat.
Without entering into detail regarding the physiological action
of light when applied locally, it may be of interest to call atten-
tion to some of its main features.
As already mentioned in discussing the general applications of
light, it constitutes a means of generating heat within the tissues
down to a depth of two inches or more, while connective heat is
far less penetrating. Moreover, besides the conversion of light
rays into heat, we have to deal with the chemical actinic rays
which also play a not unimportant part in phototherapy.
The sum total of these combined effects is as follows. There
is an increased local activity, as manifested by a pronounced
hyperemia and an augmented tissue oxidation and elimination.
The effects of radiant energy, however, are not confined to the
I40 TRANSACTIONS I. E. S. PART I
site of application, but are so diffused that remote effects are
produced in distant organs and nerve centers as a result of
peripheral or cutaneous stimulation. It is easy to understand
that the increased circulation, oxidation and elimination in the
affected part will relieve congestion and promote absorption of
exudates and deposits and the excretion of toxic materials. It
has likewise been shown by physiological investigators that the
heat production in the tissues increases phagocytosis and thus
enhances the vital resistance.
The rapid relief of pain and local spasm experienced from
light therapy is due in a great measure to the reduction of con-
gestion and to tissue relaxation. In this connection it may be
emphasized that these decided effects are brought about without
the least risk to the patient, a statement which is not applicable
unreservedly to other methods of treatment.
I shall now briefly discuss those conditions in which the local
application of phototherapy in my experience has yielded the
most satisfactory results. The employment of the parallel rays
from a high power marine searchlight as described above, applied
for 30 minutes to the spine at a distance of 10 feet, is one of
the most effectual and lasting means of relieving many forms of
spinal congestion.
In the acute stages of bronchitis or in pulmonary congestion
from almost any cause, light applications to the chest afford a
more prompt relief of chest pain and respiratory distress than
any other measure with which I am familiar. In cases of chronic
bronchitis marked benefit is obtained by prolonged daily applica-
tions of light to the front and back of the chest, continued until
marked redness and tanning of the skin is produced.
To promote more speedy absorption in pleurisy I know of no
better means than the daily use of phototherapy. In lobar and
bronchial pneumonia its beneficial influence is manifested by
marked relief of pain and dyspnea (shortness of breath) and an
improvement in the general comfort of the patient; and in cases
where resolution was delayed, it seemed to hasten this process.
I have frequently had occasion to resort to this treatment,
using cither the arc or 500 candlepower tungsten lamp, in cases
of both acute and sub-acute inflammation of the gallbladder,
TITUS : LIGHT IN THE TREATMENT OF DISEASE 141
congestion of the liver and other abdominal viscera from chronic
malaria, alcoholism and persistent intestinal auto-intoxication.
It is no exaggeration to say that my results have been far better
than when sole reliance was placed upon customary medicinal
treatment.
In the treatment of muscular rheumatism, neuritis and even
the intense discomfort associated with herpes zoster (shingles),
more rapid and lasting relief, due to diminished congestion and
nerve sensibility, will be obtained by this method than by recourse
to the various analgesics and with no risk of undesirable after-
effects.
The pain in acute middle ear catarrh (common earache), the
frontal or orbital headache accompanying acute colds, and espe-
cially involvement of the frontal sinus and ethmoid cells is
promptly alleviated by a thorough application at frequent inter-
vals of light from a 50 candlepower carbon or tungsten lamp in
a suitable reflector. To this I can testify not only from my own
experience, but I could add the testimony of many physicians
familiar with the use of this potent therapeutic agent. In chronic
ear trouble and disease of the frontal sinus and antrum, it has
proved a very valuable auxiliary by relieving the congestion and
clearing up the discharge.
It has been my privilege to witness the success of this treat-
ment in several cases of catarrhal appendicitis, and it has seemed
to me that the pain and other symptoms were more quickly
ameliorated and the necessity of surgical intervention more often
avoided than had been my previous experience.
In various types of septic conditions, such as phlebitis, so-called
milk-leg, following child-birth, or intrapelvic operations, the
use of light in the manner indicated or by means of the multiple
light dome, as employed in the Women's Hospital in New York,
has proved a well-nigh indispensable agent in gynecological
practise.
It will be found equally useful in the treatment of infected
wounds of the extremities, cellulitis, furuncles, varicose ulcers,
and localized infective processes in general.
From experience up to date there seems to be a brilliant future
14- TRANSACTIONS I. K. S. — PART I
for this measure in hastening repair in cases of delayed union
of fractures.
In an article published some time ago I reported observa-
tions which showed that it might be possible to prevent the occa-
sional deleterious effects of the X-ray by following its applica-
tion with the rays from a marine searchlight. It is very grati-
fying to me to state that subsequent experience has seemed to
confirm these results.
If, in this rather fragmentary sketch, I have been sufficiently
fortunate to impress upon you the value of phototherapy as a
safe and efficient auxiliary in the treatment of many conditions,
the object of this paper will be fully realized.
DISCUSSION.
Prof. F. C. Caldwell : It is certainly desirable for us as
illuminating engineers to know something about the curative ef-
fects of light. It seems, however, that our relation to a paper of
this sort is rather a peculiar one, in that it is something that we
know little about and are in no position to discuss. It would be
a matter of interest to know to what extent the statements that are
here made represent the consensus of opinion of the medical pro-
fession and to what extent they are the observations and views of
only the author. It seems that if the contents of this paper are of
the former class they are of great interest to us from an educative
standpoint. If, however, the paper is of a controversial nature.
we really are in no position to handle it.
Mr. John B. Taylor: The statements in the paper of Dr.
Titus are unaccompanied by the data usually required by engi-
neers or physicists to justify opinions respecting the correctness
of the author's claims. The illuminating engineer, unless he is
also a doctor of medicine, has neither opportunity nor right to
attempt to check the results reported. The engineer should,
therefore, keep an open mind and request further and more
specific facts. Until these are available it seems proper to express
the opinion that much is "not demonstrated."
There is plenty of physical evidence that X-rays and ultra-
violet light affect the body tissue and kill bacteria. Is there
similar evidence for the statement which appears three times, to
LIGHT IN THE TREATMENT OF DISEASE 143
the effect that "* * * the thermic effects of light extend to
a depth of two inches"? We may recall that the body tissue is
largely water and that water cells are regularly used for the
purpose of cutting off the infra-red or so-called "thermic rays."
Dr. P. W. Cobb: In the paper Dr. Titus lays stress on the
fact which Mr. Taylor has just mentioned, viz., the thermic
effects of light extend to a depth of two inches or more. Now,
the use of heat in the treatment of disease is, as you all know,
a very old matter. Every mother of a family knows the value of
it. But the means chiefly employed have been means which
involve conduction, as examples, the hot water bag and the poul-
tice. In more advanced therapeutics a hot air bath has been used,
where, for instance, a joint which is suffering from some chronic
trouble, may be baked, wrapped in cotton and placed in a chamber
which is heated by a lamp. The results of this treatment have
been very good in certain cases. The point that Dr. Titus wishes
to make here is that the light rays penetrate to a greater depth
than the heat that we can introduce into the tissues by any con-
duction or convection method. In using a light source such as a
tungsten filament lamp for this purpose, there is a certain limit.
We know that the infra-red radiation beyond the visible — barring
a short interval just beyond the red — is rapidly absorbed by water.
There would be then a certain amount of the energy which would
be stopped at the very surface, or at very shallow depths in the
skin. If the energy used were increased superficial burning
would be the result. It has occurred to me that there is oppor-
tunity for scientific investigation which might materially augment
the resources of the photo-theapist. It would seem possible that
by investigation of living tissues the elevation of temperature at
various depths might be determined and that, further, it would
be possible to find just which wave-lengths are superficially
absorbed and which ones penetrate the tissues deeply. Knowing
these facts, it would be possible to make screens which would cut
out the rays that are absorbed at the very surface by means of
which the superficial heating effect could be avoided and a deeper
heating effect obtained. We know, for instance, that in looking
at the hand toward the sun, there is an orange reddish light that
is transmitted through the thinner portions of the fingers. We
144 TRANSACTIONS I. E. S. — PART I
know that water will not transmit the longer-waved infra-red
radiations. Could we so screen the light that only those rays
which have a deep, penetrating power in the tissues would reach
the skin and by greatly increasing the energy get intense deep
effects without the superficial effect which might be undesirable?
I want to put this in the form of a question to Dr. Titus and ask
whether any scientific work has been done on the actual penetra-
tion of the rays into the living tissues, that is. with exact ref-
erence to their wave-length.
Mr. G. H. Stickney : Dr. Titus points out what suggests an
important application of light for the good of humanity. As
most of us are untrained in medical practise, we are unable either
to confirm or question his results. Even if only part of the bene-
fits described could be assured of realization, it would seem to me
that the subject would be well worthy of further investigation
to the end that artificial light might be better adapted to meet
such needs, and the facts of the case made more generally known.
Mr. C. O. Bond: In one of the weeklies in the East, there
appeared recently an editorial concerning the sun bath cures that
were effected at some place in Switzerland, where high altitude
and clear air gave an excess of ultra-violet light over what is
obtained in lower altitudes and through different strata of filter-
ing air. They are, it seems, accomplishing some quite remark-
able results in cures of all sorts of diseases, so much so, that
this editorial spoke with unbounded enthusiasm. If that be true,
then it is quite worth while undertaking to duplicate these condi-
tions by artificial light. But it would seem a difficult thing to do
this where there is a glass bulb surrounding the source of light at
the very beginning, because much of the ultra-violet radiation
would be lost at that point. With the searchlight scheme which the
author suggests, the glass face being removed, there is not the
same chance of losing the ultra-violet rays.
Dr. Ellice M. Alger (Communicated) : I am not competent
to discuss the technical side of Dr. Titus' paper, but there is one
point I should make. The careless listener or reader might easily
get the erroneous impression that photo-therapeutic apparatus
was about all the equipment that the physician of the future would
need. No doubt the author intended to lay special emphasis
UGHT IN THE TREATMENT OF DISEASE 145
on the very important qualification contained in the last sentence
of his paper, viz., "phototherapy is a safe and efficient auxiliary"
but not a method of treatment in itself. To use it as the doctor
advises in appendicitis or in earache would be criminal for a man
who was not competent to exercise the nicest judgment as to the
point where the case ceased to be medical and became surgical.
It would be little better for a man to treat Bright's disease and
diabetes knowing nothing of their nature or their danger signals
but with the simple faith that his therapy is good for all diseases.
Electro-therapeutics has been particularly handicapped in just
this way. Its special danger has been that it can be made useful
in many different branches of medicine, of all of which no one
human brain could have more than a smattering. It can be used
safely only by one who has a sound fundamental training and
who knows not only his own limitations but the limitations of his
medium. I am glad Dr. Titus so evidently had this in mind in
his concluding sentence.
Dr. John Wieeard Travell (Communicated) : In this paper
the many useful ways in which light may be utilized to alleviate
painful and diseased conditions of the human body have been set
forth briefly and forcibly. The limited subject has held the
speaker to a description of certain therapeutic uses of light with-
out permitting him to describe other mehods of treatment, or to
make comparison with other methods as to the degree of efficiency
in securing results. It is like reading a page in Materia Medica
in which the good qualities of a drug like digitalis are enumerated
and the many conditions in which it might be used noted. But
from such a brief perusal one must not conclude that it will act
in all these many ways better than all other agencies.
It is my fortune to be familiar alike with the therapeutic uses
of light and with Dr. Titus' method of using it in his practise,
and I feel impelled to emphasize the fact that he uses light as
an adjunct to other physical agencies and drugs, and not as a
cure-all.
Mr. R. B. Ely: Physicians have come to the office of the
central station I am connected with and asked for information
about lamps of the kind described in this paper. The only lamp
of this sort that I knew of was the "Lucudescent" lamp, which
1 4O TRANSACTIONS I. K. S. PART I
is regulated by a rheostat. Its rays I believe are more toward
the infra-red than toward the ultra-violet. A great many
physicians have come and wanted to purchase any kind of a
lamp, so long as it was a large source that they could use in some
way, apparently regardless of the spectrum of the lamp.
Another question about the electric bath. A great many com-
plain about the cost of the electric baths in residences and are
endeavoring to reduce that cost, but it has been my experience
that they would not install a tungsten lamp in place of a gem lamp
in these baths. I would like to know whether both carbon and
tungsten lamps are used for specific diseases or whether one lamp
in such a cabinet would answer all purposes.
Mr. W. R. Mott: For the last four years, the use of flame
carbons has been coming forward in the treatment of disease.
For this purpose there are used a blue flame carbon and the snow
white flame carbon which is used for general illumination.
There is a book on the medical use of light, entitled, "Light and
Energy" by Dr. Margaret A. Cleaves. I don't consider this a
particularly important book at the present moment, but it sum-
marizes an enormous fund of information. One thing that il-
lustrates its defects is that it suggests the use of calcium peroxid
in a flame carbon. Out of curiosity I tried it and had an inter-
esting result. With about 20 per cent, of calcium peroxid the
carbon did not give any important amount of light. With about
40 per cent., the carbon, after burning nearly five minutes, ex-
ploded due to dissociation of the calcium peroxid in the entire
length of the electrode.
In regard to the use of the white flame arc, it is of interest to
know that the candlepower increases nearly as the square of the
current. The exponent is about 1.8 for some direct current open
arc lamps. The white flame arc is much more powerful than any
other known agent for actinic effect.
In the treatment of disease by light, there are two chief func-
tions : one the stimulation of healthy growth, and the other the
destruction of germs. In the destruction of germs the ultra-
violet light is very strong. The best wave-length for each bac-
teria is not known.
A physician in Cleveland went to the laboratory of the National
UGHT IN THE TREATMENT OF DISEASE I47
Carbon Company to find out how to reflect ultra-violet light.
That is not a simple proposition. In a book by Landolt and
Bornstein, some data are given on the reflecting power of several
materials. At a wave-length of 305^/i in ultra-violet the reflecting
power is :
Reflecting power
Metal in per cent.
Alloy (69 per cent. Al, 31 per cent. Mg) 72.2
Nickel plated 44.2
Copper 25.3
Platinum 39.8
Gold 31.8
Silver 9. 1
Silver in the red has a reflecting power of about 90 per cent.
One of the problems in the design of a lamp for therapeutic
purposes is to reflect those rays which are required. In some
cases the ultra-violet rays are wanted in others they are not.
The open flame arc gives off fumes which are objectionable
and should be removed by good ventilation. I have found
in the use of the white flame arc for the photographic studio, that
a small piece of ammonium carbonate placed in the enclosed
chamber will eliminate the bad effects of the nitric acid produced
by all open arcs.
I have tried an experiment with the snow white flame carbons
and found that glass of an ordinary window pane (0.08 in. thick),
destroyed at least 50 per cent, of the photographic power, and
with another chemical I found that a greater portion, as much as
two-thirds, of the light was destroyed. The question of specially
designed glass therefore, is important. If ultra-violet rays were
required then quartz would be necessary. If stimulation were
desired then other glasses specially selected for each treatment
would be advisable.
Dr. E. C. Titus (In reply) : The great majority of physicians
do not themselves employ light in the treatment of disease, but
do refer patients frequently to institutions where it and other
physical agencies are in use.
The researches of Finger of Vienna demonstrated that by
applying on ointment consisting of 4 per cent, esculin in glycerin,
(the active principle of horse chestnut) to the skin that 80 per
2
I48 TRANSACTIONS I. E. S. PART I
cent, of the ultra-violet rays penetrate to the deeper tissues where
ordinarily said rays are arrested by the skin.
The researches of Finsen of Copenhagen seem to prove that
both the ultra-violet and the luminous rays exercise their char-
acteristic influence not alone upon the surface of the skin, but
also on the deeper parts as evidenced by their inhibitory action
upon both local and deep tubercular processes.
Further, Kellogg of Battle Creek, Mich., the originator of the
electric light bath cabinet, has shown that the processes of elim-
ination of deleterious substances retained in the tissues are
promptly intensified through the increased activity of the skin and
of the kidneys, with elimination of waste products, and the
doubling in quantity of the carbon dioxid eliminated by the
lungs, as the result of the constitutional effects of the intense
luminous rays upon the surface of the body.
One fact which Dr. Cobb seemed to lose sight of is that the
body fluid is practically a circulating saline solution whose con-
ductivity for light energy is one of the best known. Photo-
graphic plates have been affected by light through two or more
inches of living tissue. In accordance with the law of conserva-
tion of energy, the luminous rays which are carried into the
tissues are there converted into heat, inducing a physiological
hyperemia and tissue oxidation or more active metabolism.
In connection with Mr. Mott's remarks it would seem proper
to emphasize that the ultra-violet rays are used principally for
local effects on the skin and superficial conditions, as for the
dissipation of so-called port wine marks.
The writer had attempted to show the therapeutic applications
of the full spectrum or more particularly of the luminous rays as
an efficient auxiliary in the treatment of many painful and other
disease conditions.
Referring to Mr. Ely's remarks, — it is the diffused and intense
light energy employed in a cabinet bath, properly ventilated as
pointed out in the paper, to which we attribute its chief thera-
peutic efficiency.
LUCKIKSIi: NEW HIGH-EFFICIENCY LAMP 149
THE APPLICATION OF THE NEW HIGH-EFFICIENCY
TUNGSTEN LAMP TO PHOTOGRAPHY*
BY M. EUCKIESH.
Synopsis: The results of a general study of the photographic value
of the radiation from the new gas-filled tungsten lamp are presented. A
comparison has been made of this new lamp with the mercury-vapor lamp
and the older type of tungsten lamps. The effect of voltage on actinicity
has been studied. A scheme which has been developed for reducing glare
from this lamp when used in portrait photography is described. Other
photographic data are given. The fundamental principles of the lighting
of studios are dwelt upon and the application of the tungsten lamp to
various branches of photography are briefly described. Data on present
practise in moving picture production studios are given and desirable
accessories are shown.
The recent great increase in the efficiency of tungsten lamps
of large size, brought about by introducing the filament in an inert
gas, has made it possible for the new lamps to invade fields in
which the incandescent lamp heretofore has not been an impor-
tant factor. One of the interesting new fields in which the gas-
filled tungsten lamp is meeting with considerable success is that
of photography. Owing to the higher operating temperature of
the filament the luminous efficiency is considerably increased and
the actinic value of the light for ordinary plates even in a greater
ratio. The natural characteristics of the tungsten lamp, such as
portability, steadiness, ease of operation, unvarying quality, con-
tinuous character of spectrum, and high efficiency, are valuable
allies to the most essential characteristic, namely, radiant energy
of high actinic value. A study of the actinicity of the light from
gas-filled tungsten lamps has shown that this lamp is destined to
become an important factor in photographic procedure.
Sensibility of Ordinary Photographic Plates. — In ordinary
photography only the rays of wave-length from 0.30 p to 0.50 n
are of appreciable importance. In fact the ultra-violet radiation
in daylight practically ends at 0.30 n, the rays of shorter wave-
* A paper read at a meeting of the Nevr York Section of the Illuminating Engi-
neering- Society, January 14, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
i5o
TRANSACTIONS I. E. S. — PART I
length being absorbed before reaching the earth. Ordinary clear
glass begins to absorb ultra-violet rays at 0.35 /* and becomes
opaque for rays of shorter wave-length than 0.30 fi. Optical
systems used in photographic apparatus usually being made of
glass, the radiation of shorter wave-length than 0.30 /1 is of no
interest. Ordinary plates highly sensitive only to 0.50 p can be
made relatively more sensitive to rays of longer wave-length, but
this procedure usually results in greatly decreasing the speed so
that ordinary plates are far from orthochromatic. In ordinary
portraiture there is no urgent need for plates sensitive to all the
"■.;...-;!
0
4*
Kig. i.— Spectral energy distribution in radiation from various sources.
visible rays because quite satisfactory modeling of the subject
can be done in light and shade.
Spectra of Common Light Sources. — In Fig. 1 are shown the
spectral distributions of energy in the spectra of the light from
tungsten lamps as compared with skylight and noon sunlight.
These are plotted with equality at 0.59 \i which indicates the
relative values of energy of various wave-lengths for approxi-
mately the same integral values of luminous intensity. No
spectro-photometric data on the latest arc lamps are available.
The spectrum of the mercury arc, being a line spectrum, is not
luckiesh: new high-efficiency lamp 151
plotted; but its actinic value for ordinary plates is much more
nearly equal to that of daylight than that of the new tungsten
lamp. In some other respects, however, it is not as desirable
as the latter for photographic purposes. It is seen that the new
high efficiency tungsten lamps emit relatively much more of the
so-called actinic rays than the vacuum type.
Sensibilities of the Eye and Ordinary Photographic Plate. — In
Fig. 2 are shown diagrammatically the spectral sensibilities of
the eye and of the ordinary photographic plate for rays of equal
energy value. While it is a well-known fact among those
acquainted with the science of photography that the sensibilities
of the eye and the ordinary photographic plate are far different,
it is not so well known to many interested in the art of photog-
_, , , , 1 _
Fig- 2.— Spectral sensibilities of the eye and the ordinary photographic plaife
for rays of equal energy value. 1 * Qf ofT
raphy. One of the aims of the investigator in the science of
photography is to produce a high speed plate sensitive relatively
to the various spectral rays in the same general manner as the
eye. This has not yet been done. However, this is no great
handicap in ordinary portraiture. On the other hand, such a
plate would be invaluable in landscape and much indoor pho-
tography involving the reproduction of colored objects in true
values.
Relative Actinicities of Mercury Arc and Tungsten Lamps. —
In order to study the actinicity of an illuminant1 it is advan-
tageous to arrange an apparatus which will give a number of
different values of illumination on the same plate simultaneously.
This is easily done by means of a disk having openings of differ-
1 Luckiesh, M., New Tungsten Lamps in Photography; Electrical World, July 19, 1914.
152 TRANSACTIONS I. E. S. PART I
ent degrees. The disk used by the writer had ten openings vary-
ing in size from 10 deg. to 180 deg. The plate and disk were
enclosed in a velvet-lined box with a small aperture in one end
covered with ground opal glass which was chosen after finding
that it transmitted practically the same rays that clear glass trans-
mits and in the same relative proportions. This ground glass was
necessary in order to obtain well-defined circular strips on the
photographic plate, to obviate "pinhole" effects, and to cut down
the light so that a reasonably long exposure could be given. Ex-
posures should be sufficiently long so that they can be accurately
timed with a stop-watch. In a given case both the exposure of
the plate and the illumination on the disk were kept constant.
Several plates were exposed for each illuminant with the usual
unexposed "fog-strip" on each. These were developed under the
same conditions and finally measured for transparency by means
of a Martens polarization photometer. In order to interpret the
data the following definitions are presented :
light transmitted
Transparency = T =
light incident
Opacity = O = -~
Density = D = log O = log = .
In Fig. 3 are plotted the results obtained on a Seed 26 plate
with a mercury-vapor tube and three tungsten lamps. The plate
chosen is representative of the sensibility of common photo-
graphic plates. The densities plotted against the logarithms of
the illuminations produce a curve which is straight over a con-
siderable region. This region is the accepted working range of
the plate. Data of this character are so influenced by the con-
ditions of exposure, development, kind of plate, etc., that no
more than a general idea of the relative actinicities can be gained
without presenting too extensive data for a paper of this char-
acter. It is seen that for an ordinary photographic plate the
light from a mercury arc is three to four times more actinic than
the light from the gas-filled tungsten lamp operating at 20 lumens
per watt. Owing to the compactness of the light source of the
tungsten lamp, however, the light is more efficiently controlled or
euckiesh: new high-eeficiency lamp
153
directed than in the case of an extended source. This tends to
overcome the disadvantage of the gas-filled tungsten lamp with
its lower actinic value per lumen.
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Fig. 3.— Relative actinicities of different illuminants for an ordinary
photographic plate (Seed 26).
Effect of Voltage on Actinicity of Tungsten Light.— -The influ-
ence of voltage or filament temperature on the actinic value of
the light from the gas-filled tungsten lamp is shown in Fig. 4.
2 3 4 5 6 8 10 20 40 60 80 100 MO 180
RELATIVE ILLUMINATION
Fig. 4.-Effect of voltage on the actinic intensity of a 1,000-watt, 115-volt, nitrogen-
filled tungsten lamp for an ordinary photographic plate (Seed 30).
A 1,000-watt gas-filled tungsten lamp operating normally at 115
volts and 18 lumens per watt was operated at three voltages and
the relative actinicities of the light determined for an ordinary
'54
TRANSACTIONS I. K. S. PART I
photographic plate (Seed 30). It is seen that the actinic value
increases very greatly as the voltage is increased above normal.
For instance, to produce a photographic density of unity (trans-
parency 10 per cent.), the relative amounts of radiation were 68
and 34 respectively for normal voltage (115) and 135 volts.
Thus it is seen that an increase of 17 per cent, in voltage above
normal doubles the actinicity of the light from this lamp for the
plate used. In this experiment the illumination was allowed to
increase with the voltage ; that is, the position of the lamp was the
same for the three voltages.
Effect of Voltage on Actinicity per Unit of Light Flux. — In
order to show the influence of voltage on actinic value per lumen
of visible light, another experiment was performed in which the
1
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RELATIVE ILLUMINATION
Kig. 5.— Effect of voltage variation on the actinicity of the radiation from a 1,000-watt,
115-volt, nitrogen-filled tungsten lamp; luminous intensity constant.
illumination falling on the multi-sector disk was kept constant.
The results are shown in Fig. 5. This shows that the radiation
affecting ordinary photographic plates increases more rapidly with
voltage than does the total luminous radiation. The figures at
the right represent different voltages. In this case a Seed 26
plate and the same lamp (1,000-watt, 115-volt gas-filled) as in
the foregoing experiment were used. It is well to note that
actinicity depends upon the sensibility of the plate under con-
sideration. For instance if a plate is more sensitive to the violet
or blue rays the actinicity of the radiation from a tungsten lamp
will increase more rapidly than the luminous intensity with in-
creasing voltage. However, the actinicity of this radiation for a
luckiesh: new high-efficiency lamp 155
truly orthochromatic plate will increase in the same ratio as the
luminous intensity. In other words, an increase of 17 per cent,
in voltage would not double the actinic value for an orthochro-
matic plate, but would increase it only 67 per cent. It should be
noted that the data represented in a given curve in Fig. 5 are
for constant illumination as measured with a direct comparison
photometer. It is thus seen in Figs. 4 and 5 that a great gain in
actinic value can be obtained by increasing the voltage above
normal. This led to an early trial of the scheme and there are
outfits on the market employing this principle. An increase in
voltage, however, results in a decrease in the life of a tungsten
lamp ; so that the writer was led to another method of producing
light of high actinic value which could further be used where
lamps were burned for long periods such as in taking moving
pictures. The method which also has other advantages will be
discussed later.
Orthochromatic Photography. — There are some kinds of pho-
tographic work (relatively few, however) that require an accu-
rate reproduction of color values in light and shade such as in
the photography of paintings and the tri-color printing process.
Here orthochromatic plates are necessary and also a light source
emitting all the visible rays. There are no truly orthochromatic
plates on the market and where accurate work is desirable a very
accurate filter is necessary to alter the spectral character of the
light which reaches the plate so that the sensibility of the plate
approaches closely to that of the eye. Most of the so-called ortho-
chromatic plates available are far from being truly orthochro-
matic. Some are not even sensitive to red rays to an appreciable
extent. Many show a relatively insensitive region at about 0.50 fi.
The high-efficiency gas-filled tungsten lamp is quite satisfactory
for most of the work in orthochromatic photography. Its light
has all the visible rays, which is quite essential. Owing to the
preponderance of yellow, orange and red rays, it is unnecessary
to use such a slow filter with this light as with daylight for most
so-called orthochromatic plates. This means a somewhat higher
speed for rough orthochromatic work than with daylight. How-
ever, for an orthochromatic plate such as the Cramer spectrum
plate it will be found that there is too much of the radiation in
If-'' TRANSACTIONS I. E. S. PART I
the long- wave visible region in the light of a gas-filled tungsten
lamp. In other words this plate has been over-sensitized to the
orange and red rays, which condition, however, is rare. As
already stated the need for orthochromatic plates in the portrait
studio is not urgent.
Adapting the Tungsten Lamp to Portrait Photography. — Owing
to the fact that light from the gas-filled tungsten lamp is only
one third to one fourth as actinic as daylight, it is to be expected
that a condition of glare is liable to obtain in portrait photog-
raphy- where a reasonably high speed is desirable. Such has
been found to be the case. It is quite desirable to have sufficient
actinic value per lumen of light in order to permit lenses to be
used at the smaller apertures and yet to insure sufficient speed.
The lamp, of course, can be burned above normal voltage for the
brief period of exposure in portrait work. However, this pro-
cedure calls for special apparatus and introduces an undesirable
flash-light effect. Further, it may have an appreciable effect upon
the life of the lamp, although this is at present an unknown quan-
tity to the writer. Certainly any appreciable amount of burning
at a voltage sufficiently excessive to warrant the use of special
apparatus would seriously decrease the life of the lamp. For
continuous work such as the making of moving pictures, the
lamps cannot be operated at any great increase above normal
voltage without a very considerable decrease in the life of the
lamp. The low actinic value of the light with a consequent con-
dition of glare when sufficient illumination is used to gain high
speed cannot be overcome by the use of diffusing screens.
It early occurred to the writer that some selective method was
necessary to adapt the new tungsten lamps in the best manner to
portrait photography. Experiments were made to produce a
glass of such transmission characteristics that practically all the
rays to which ordinary plates were sensitive would be transmitted
while the non-photographic but highly luminous rays would be
reduced. It was also necessary that the glass be quite trans-
parent to infra-red rays, because too much energy absorbed by
the bulb would be liable to cause serious trouble. Reference to
Fig. 2 shows that it should be possible to produce such a glass.
5 L,uckiesh, M., Adapting the Tungsteu Lamp to Portrait Photography; Eleclncal
World, November 14, 1914.
LUCKIESH : NEW HIGH-EFFICIENCY LAMP 1 57
Of course a highly efficient glass must be as transparent to the
ultra-violet rays as the clear glass of the camera optical system.3
Such a glass was made with a transmission for the total visible
light from the 1,000-watt, 115-volt, nitrogen- filled tungsten lamp
of about 30 per cent, while the actinic value was inappreciably
affected for ordinary photography. A further aim was to reduce
the ordinarily non-actinic rays in just the right proportions so
that a pleasing light, apparently white in appearance, was ob-
tained. A glass satisfactory in all these respects was obtained.
It was found to transmit about 85 per cent, as much of the total
radiation as clear glass, thus no trouble was to be expected from
excessive local temperature. This glass must not be confused
with the 'daylight' glass4 recently developed by the writer. The
two glasses are far different, for the daylight glass was developed
for the purpose of altering only the visible rays of tungsten light
to a spectral equality with daylight, whereas the glass here
referred to has for its purpose the transmission of the ordinary
photographic rays and the reduction of the remaining visible
rays to such a degree that an apparent match with daylight is
obtained.
The result of this development is a light that appears to be of
the same color as daylight and a light of approximately the same
actinic value per lumen. This means a great deal to the pho-
tographer. No accessory apparatus is necessary ; merely a socket,
lamp and reflecting apparatus. The light being practically of the
same apparent color and actinicity as daylight it can be used to
reinforce daylight. This has been done in many instances. When
daylight fails it can be used satisfactorily alone with the same
speed as daylight, thus the photographer does not need two
different instincts for making exposures. Burning at normal
efficiency, there is no danger from burn-outs, such as is present
with excessive over-voltage apparatus, and the lamp can be used
for such purposes as the production of moving picture films where
long periods of continuous burning are necessary. It has proved
successful in the latter field. The lamps have also been used suc-
* Luckiesh, M., Ultra-violet Radiation; Electiical World, June 15, 1915. Luckiesh, M.,
Glasses for Protecting the Eyes ; Trans. I. E. S., No. 5., 1914.
4 lyUCkiesh, M., Artificial Daylight ; Electrical World, September 19, 1914. Luckiesh
and Cady, Artificial Daylight; Trans. I. E- S., No. 8, 1914.
158
TRANSACTIONS I. E. S. — PART I
cessfully for home portraiture, and photographers have found
them readily portable for indoor work outside of the studio.
Difference in Transparency of Blue Glasses for Ordinary Pho-
tographic Rays. — As will be seen from Fig. 2, the glass will be a
bluish color; but in order to show that any ordinary blue glass
will not be satisfactory the data in Fig. 6 are given. Out of a
number of samples of glass the writer asked an assistant to
choose two blue glasses. The assistant is somewhat trained in
color-work and therefore understood clearly what 'blue' means.
The two samples were exposed to the total light from the gas-
filled lamp under the conditions previously described in the use
of the multi-sector disk. The results show the great difference
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RELM"IVL ILLUMINATION
Fig. 6.— Relative actinicities of the radiation from a 1,000-watt, 115-volt, gas-filled,
tungsten lamp after passing through two different specimens of blue glass.
This illustrates that there is a great difference in the transparency of blue
glasses for actinic rays. Ordinary plate used.
in the transparencies of the two samples for the so-called actinic
rays. At a density of unity the radiation passing through one
sample was about one third as actinic as the radiation which
passed through the other. Experiments with other media also
showed great differences in their transparencies to ordinary
actinic rays. Many blue dyes were unsatisfactory owing to lack
of permanency.
In order to show that the glass finally chosen for use in the
bulbs of the gas-filled tungsten lamp for photographic purposes
is highly transparent to the rays affecting ordinary plates, the
spectra of the light from this lamp through two samples of the
• srr
Fig. 7--Effect of proposed glass on various Seed plates. C-clear glass. A and B-Samples
of proposed glass transmitting 50 per cent, and 35 per cent, of total light from a tung-
sten-filament lamp operating at 18 lumens per watt.
Fig. 8.— A method of using the new high-efficiency special blue-bulb tungsten-filament
lamp in a portrait studio.
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pig. 9._An example of photostat lighting. Four i,ooo-\vatt, 115-volt, tungsten-filatnent
lamps in white-enamelled, angle, steel reflectors.
luckiesh: new high-efficiency lamp 159
proposed glass of different densities, as compared with the spec-
trum of the light through clear glass, are shown for six ordinary
plates. It is seen in Fig. 7 that there is no visible reduction in
the actinic rays for these first six plates on the left. To illustrate
how insensitive ordinary plates are to the green and yellow rays
attention is directed to the mercury-vapor comparison spectrum.
The green (0.546 fi) and yellow lines (0.577 /* and 0.579 f0> t0
which 95 per cent, of the visible light must be credited, do not
show on the reproductions which are made from ordinary plates.
In some cases the green line shows very faintly on the plate.
Here it is well to note that these spectograms were made with a
prism spectrograph and owing to the much greater dispersion of
the prism for the rays of short wave-length the plates seem to
be more sensitive to rays at about 0.46 fi. This is not the case,
for they are most sensitive to rays close to the short-wave end
of the visible spectrum.
It may occur to some that in the rare cases of orthochromatic
photography a lamp equipped with a bulb or screen of this glass
would be unsatisfactory. There is some reduction in speed in
this case, but not an excessive amount as is shown for three
so-called orthochromatic plates in Fig. 7. All the rays are yet
present in this light after passing through the blue glass. There
is really some advantage in many cases of orthochromatic pho-
tography in using the glass developed because the light after
being altered by the blue glass screen is a rough approximation
to daylight and therefore the same filters that have been used
with daylight can be used with this light which would not be true
with the unaltered light. Further it should be noted that the
light from the gas-filled lamp after passing through the blue glass
is just as actinic as daylight for any orthochromatic plate. In
other words, there is produced a 'photographic daylight.'
Spectro-photography. — A note on the study of spectral sensi-
bilities of plates may not be out of place. Owing to the variable
dispersion of a prism, the rays of short wave-length are greatly
weakened by the greater dispersion in this region than the rays
of longer wave-length. The spectra of most artificial light sources
are weakest in the ultra-violet region, which, combined with the
weakening due to excessive dispersion, causes difficulty in obtain-
l6o TRANSACTIONS 1. K. S. — PART I
ing the spectral sensibilities of plates. A grating spectrograph is
more desirable than one of the prism type, owing to the normal
spectrum obtained. However, for some work the prism spectro-
graph can be made more satisfactory by allowing for the weaken-
ing due to dispersion by means of a screen or revolving disk. If
the spectrum of a continuous light source of known spectral
energy distribution be photographed on a plate and a positive be
carefully made from this negative, the resulting positive can be
placed in a proper position in front of the plates to be used and
thereafter (provided they are the same plates) more satisfactory
results will be obtained, owing to the elimination of the weaken-
ing due to excessive dispersion in the short-wave region. Another
method of overcoming both the non-uniform spectral energy dis-
tribution and dispersion is found in making a templet in a revolv-
ing disk compensating for both of the foregoing with the result
that the photographic effect for energy of each wave-length would
be immediately that for equal amounts of energy throughout the
whole spectrum. A screen which will compensate for either the
variable dispersion or the non-uniform spectral energy distribu-
tion of the light source (or both) can be made by producing a
cam of the proper character which when uniformly revolved
would move a photographic plate across an image of a straight
tungsten filament. The cam would cause the plate to move
at just the proper non-uniform rate to cause a varying photo-
graphic effect on the plate of just the right amount at positions
corresponding to the various wave-lengths so that the negative or
positive, as the case may be, could be used as a screen for com-
pensating the effects of non-uniform spectral energy distribution
or variable dispersion or both. Possibly these schemes have
already been applied. At any rate they are desirable aids where
considerable spectro-photographic work is being done.
THE LIGHTING OF PORTRAIT STUDIOS.
It certainly would be presumptious for the lighting specialist
to attempt to teach the portrait photographer how to light his
subjects, for lighting is the basis of the photographer's art. The
writer has often recommended that the lighting specialist consult
the photographer and his product, for there is much to be gained
from such a procedure. However, the lighting specialist can be
LUCKIESH : NEW HIGH-EFFICIENCY LAMP l6l
of assistance in the portrait studio because he has an acquaintance
with the laws and methods for obtaining results desired by the
photographer. In other words, the photographer knows the
effects he desires, but the lighting specialist is perhaps better
acquainted with the optical laws which govern the results.
The lighting of subjects in the portrait studio is practically
entirely a matter of light and shade.5 The character of shadows
depends upon the position of the light source, the solid angle
subtended by the source at the shadow-forming object, and the
amount of scattered light reaching the object. The position of
the light source determines the direction of the shadows, the
area of the light source or more correctly the solid angle sub-
tended by the light source at the point of interest, determines the
character of the edge of the shadows, and the amount of scattered
light determines the density of the shadows.
Pig. io.— a— shadow produced by a point source of light amid non-reflecting sur-
roundings; b— shadow produced by a point source of light and io per cent,
scattered light; c— shadow produced by source of varying area and io per cent,
scattered light.
Obviously a point source of light in a perfectly black room
would produce black and sharp shadows on a diffusely reflecting
surface. If the walls and surroundings were of such a reflecting
power that io per cent, of the total light reaching the object is
scattered light, a shadow on a diffusely reflecting surface would
be one tenth as bright as the surface receiving the total light,
but would yet remain sharp in outline. By varying the area of
the light source the shadows would become less defined, but the
io per cent, of scattered light is still effective. Some combination
of these possible conditions is desired by the photographer.
The foregoing conditions are roughly represented in Fig. io.
The receiving surface is here assumed to be a perfect diffusely
reflecting substance. The third case, c, is not an exact represen-
5 Luckiesh, M., Light and Art : Lighting Jour.. March, 1913. Luckiesh, M., Light
and Art ; American Gas Inst., October. 1913.
1 62
TRANSACTIONS I. E. S. — PART I
tation, for the sloping line would be more or less curved owing
to the different distances of the elements of the surface of the
light source from the shadow-producing point.
The lighting of a studio by means of a diffusely transmitting
skylight is illustrated in Fig. II. The skylight, ef, is for sim-
plicity assumed to be vertical as is the case in many studios. Its
shadow-producing qualities are dependent upon the solid angle,
epf, (the dimension perpendicular to the plane of the paper can
be assumed equal to the dimension shown for simplicity). Scat-
tered light of course is controlled by screens and the direction of
the shadows by curtains and the orientation of the subject. Often
the amount of light passing through the skylight (the flux den-
sity) is insufficient to insure reasonably short exposures, so the
Fig. ii.— Illustrating the dependence of shadow-producing effect of extended
sources upon the solid angle subtended at the subject by the source; that
is, upon the size of the source and its distance from the subject.
subject must be moved closer to the skylight. This means that
the solid angle is greatly increased with a result of apparent
flattening in the photograph. In order to produce satisfactory
modeling, a source too large in area is undesirable. This necessi-
tates greatly reducing the skylight area by screens or moving the
subject further from the skylight, both cases often resulting in
an undesirable decrease in the illumination of the subject. Re-
ferring again to Fig. 1 1 it is seen that the light source can be
decreased in area as the subject approaches it. Thus the shadow-
producing qualities of the three sources ab, cd, and ef are the
same, if the dimension perpendicular to the paper is assumed to
vary in the same manner and the sources are uniformly bright.
A great advantage experienced in the use of artificial lighting
LUCKIESH : NEW HIGH-EFFICIENCY LAMP
163
is that studios can be reduced very much in size owing to the
greater amount of light obtainable per unit area of the source
than in the case of the average skylight in cities and that the sky-
light can be dispensed with. Thus the skylight, ef, in Fig. 11 can
be replaced by an artificial lighting outfit covered by a diffusing
medium of much smaller actual size, ab, without altering the solid
angle, fpe, and therefore without changing the shadow-producing
effect.
Accessories for Tungsten Lamps. — The only essential acces-
sories for tungsten lamps are a socket, a reflector, and a diffusing
screen. In general angle reflectors such as those shown in Fig. 12
are found the most convenient. There are many standards al-
ready available of the same general character as shown in Fig. 13.
These should be readily adjustable for height and portable. As
Fig. 12.— White enamelled steel reflectors suitable for photographic purposes.
would be expected, many photographers desire to carry out their
own ideas as to apparatus for containing the lamps. This was
one of the reasons for deciding to adapt the scheme of using the
selectively transmitting colored glass, proposed and developed by
the writer, to the lamp bulbs. Doubtless there are many cases
where the glass could be used as a screen in front of the reflector,
but the colored bulb presents a complete unit. This has been used
behind various kinds of artificial "skylights" or windows. A
satisfactory arrangement was found where a photographer had
placed three of the special photographic lamps in an asbestos
lined vertical box covered on one side with tracing paper. The
middle lamp was hung somewhat lower than the others and the
tracing cloth immediately in front of it was replaced by thin silk
of less diffusing property with a result that a more directed effect
3
164
TRANSACTIONS I. E. S. — PART I
was obtained. Translucent and opaque screens were placed in
various positions over the diffusing front depending upon the
desired result. Some photographers have combined their special
lamps with a mercury arc equipment already in their possession.
Needless to say the ghastly appearance of the persons in the
studio can thus be largely eliminated.
Fig. 13.— A standard for use with the gas-filled, 1,000-watt tungsten-
filament lamp in portrait photography.
Here it might be well to bring to the attention of the photog-
rapher the practise of using the fluorescent reflectors with mer-
cury arc lamps. This reflector is an excellent development, but
the red and orange rays emitted by it, due to fluorescence, are
obtained very largely at the expense of the ordinary actinic rays.
luckiesh: new high-efficiency lamp 165
A more efficient scheme photographically would be to use the
mercury arcs with white reflectors and eliminate the ghastly
appearance of the persons in the room by the addition of tungsten
lamps which would also contribute toward the actinic value of
the total light. However, in general the writer would not recom-
mend the use of a combination of two different kinds of illumi-
nants where both are appreciably different in actinicity and color,
owing to confusion which would result unless the light were well
mixed by means of a diffusing screen.
In Fig. 8 is shown a photograph of a studio where two of
the special photographic lamps are used in separate portable
standards. Here it will be noted one unit is placed on each side
of the front of the subject, but at quite different distances. Many
photographers prefer to use the primary sources on one side of
the subject, depending upon reflecting screens for lighting the
opposite side sufficiently. The writer believes that in either case
two units are desirable for satisfactory modeling and the majority
of photographers with whom he has discussed the matter are of
the same opinion. Of course the units can be placed behind the
same diffusing screen, but the two sources seem to be necessary.
Regarding the speed at which portraits can be made with the
special photographic lamp, it is sufficient to state that the expos-
ures are the same as for daylight. This is not true with the clear
lamp because it is impossible to obtain sufficient actinic value to
insure success with short exposures without producing a condi-
tion of glare which is not conducive to the production of satis-
factory pictures, unless excessive over-voltage is applied.
Printing and Enlarging. — The tungsten lamp has already
played an important part in printing. The problem presents no
difficulties and it is very easy to experiment with the lamps for
this purpose. Here there is no need for the special blue-bulb
photographic lamp, the purpose of which is to eliminate glare
where human subjects are being photographed. The writer has
seen many successful printing outfits employing various sizes of
gas-filled tungsten lamps.
In enlarging, the new lamps find a newer field. Here there are
two general forms of apparatus available; these are shown in
Fig. 14. The upper illustration shows a satisfactory arrange-
i06
TRANSACTIONS I. E. S. PART I
merit for high speed. Where a condenser is used the light source
should be compact. Concentrated-filament, gas-filled tungsten
lamps have proven satisfactory for this purpose; the exposures
being only a few seconds in duration. A cheap outfit is repre-
sented in the lower illustration. Here the lamp only is contained
in a white enamelled reflector. Over the aperture a ground glass
is placed and the negative is viewed against it. Owing to the
greater loss of light due to the absence of a light-gathering con-
denser the exposures are many times greater than in the other
case. However, satisfactory enlargements can be made in a
reasonable length of time.
Of course the variations in the schemes for printing and
Fig. 14. — A— concentrated tungsten-filament lamp; B— negative: C— condensers;
D— ground glass; E— lens; F— enlargement.
enlarging are manifold, so that it seems hardly worth while to
do more than present the chief principles. However, a special
field of interest is the lighting for photostats. This is best
described by the illustration, Fig. 9. Here as many as four
1,000-watt, gas-filled tungsten lamps are used depending upon
the size of the subject. Exposures of only a few seconds are
necessary for satisfactory results.
Moving Picture Production Studios. — The lighting for mov-
ing picture production studios is a far different problem from
that for ordinary portrait and commercial photography. In this
field artificial light sources are excessively taxed in order to fur-
nish sufficient actinic rays so that fully timed pictures can be
luckiesh: new high-efficiency lamp 167
made in one sixty-fourth of a second. Pictures are made at the
rate of sixteen per second, but considering the time during which
the film is moving when the shutter is closed, and further allow-
ing for the period during which the lens is not working at full
aperture, the actual exposure is perhaps only one fourth as long
as would be indicated by the rate of sixteen per second.
There appear to be two general classes of production studios.
In one class the lighting is permanently installed in position and
relatively large areas (approximately 18 ft. (5.48 m.) by 32 ft.
(9-75 m0 are lighted. In the other general class the lighting
apparatus is portable and relatively smaller scenes are usually
lighted. Both classes are found combined in other studios.
Doubtless both general schemes have their own advantages, but
it appears to the writer after visiting a number of studios that
the scheme of using portable lighting apparatus makes possible
better effects in general and is the more economical in space,
electrical energy, and equipment. Certainly better lighting effects
can be obtained in many cases for the scenes are continually
changing which demands a flexible lighting system in order to
obtain the best possible effects. Possibly some producers find
these advantages offset by the desirability of order.
In order to give an idea of the lighting requirements in mov-
ing picture production studios the following data on lighting
equipment required in certain observed sets are presented.
I. Set about 16 ft. by 30 ft. (4.9 by 9.1 m.).
124 mercury-vapor tubes, d. c, 112 volts, 3.5 amperes.
Energy used, about 50 kw.
Lamps arranged in banks of 8 each.
Placed 48 overhead inclined at about 30 deg. from horizontal and
12 ft. (3.65 m.) from floor.
64 on one side in banks two tiers high.
12 at front 7 ft. (2.1 m.) above floor.
Actors worked to within 10 ft. (3 m.) from front lights.
II.
Set about 16 ft. by 25 ft. (4.9 by 7.6 m.).
24 carbon arcs, a. c, 220 volts, 14 amperes.
Energy used, approximately 50 kw.
Placed 16 overhead and 8 in front about 8 ft. (2.4 m.) from floor.
Actors worked to within 10 ft. (3m.) from front lights.
1 68 TRANSACTIONS I. E. S. — PART I
III. Set about 14 ft. by 20 ft. (4.3 by 6 m.).
18 carbon arcs, d. c, no volts, 20 amperes.
2 30-ampere carbon arcs in series for flood light through a window.
Energy used, approximately 43 kw.
Placed 12 in front and 6 on side near front from 4 to 7 ft. (1.2 to
2.1 m.) from floor.
Actors worked to within 5 ft. (1.5 m.) of front lights.
IV. Set about 15 ft. by 15 ft. (4.5 m.).
12 carbon arcs, d. c, no volts, 20 amperes.
Energy consumed, approximately 27 kw.
Placed in front overhead in two rows about 8 ft. and 9 ft. (2.4 and
2.7 m.) from floor.
Actors worked to within 7 ft. (2.1 m.) of front line of lamps.
V. Set about 12 ft. by 24 ft. (3.6 by 7.3 m.).
48 mercury arcs, d. c, no volts, 3.5 amperes.
2 carbon arcs, d. c, no volts, 28 amperes.
2 carbon arcs, d. c, no volts, 30 amperes.
3 quarts mercury arcs, d. c, no volts, 3.5 amperes.
The 3 quartz mercury arcs and 2 carbon arcs were in front and the
48 mercury arcs were distributed on one side with the excep-
tion of two banks of 8 each which were near the front on the
other side. None overhead. The 2 30-ampere carbon arcs
were on the side near the front and about 10 ft. (3 m.) from
the floor. These gave a marked effect in the picture. This
appeared to be an exceptionally intelligent attempt to obtain
good lighting effects.
Energy consumed, about 33 kw.
Actors worked to within 7 ft. (2.1 m.) of front line of lamps.
IV. Set about 10 ft. by 10 ft. (3 m.).
11 1,000-watt gas-filled tungsten lamps, no volts.
Placed in front corners about 8 ft. (2.4 m.) from floor. More
lamps on one side than the other.
Energy consumed, 11 kw.
Light well controlled by angle reflectors.
Actors worked to within 5 ft. (1.5 m.) of front line connecting the
lamps.
VII. Set about 10 ft. by 15 ft. (3 by 4.5 m.).
16 1,000-watt special blue-bulb, gas-filled tungsten lamps, no volts.
Placed 8 in front, 6 on side near front, 2 overhead.
Energy consumed, 16 kw.
Actors worked to within 7 ft. (2.1 m.) of front.
Of course the wattage necessary depends upon the actinic value
of the illuminant used and especially upon the area of the scene.
IvUCKIESH : NEW HIGH-EFFICIENCY LAMP
169
The preceding data will be useful in estimating the magnitude of
an installation, the area and character of the scene being known.
There appears no field where the lighting expert is more needed.
Notwithstanding the fact that a large number of units are neces-
sary in order to obtain sufficient illumination of high actinicity
for making moving pictures a great deal of light was observed
to be lost by lack of attention to light-controlling accessories.
The tungsten lamp can successfully be used in moving picture
production studios, but care should be exercised in conserving
the light for use on the scene. This lamp, owing to its compact-
Fig. 15.— A method of supporting tungsten-filament lamps in moving
picture production studios.
ness, readily lends itself to a high utilization efficiency which
must be realized in order to insure success owing to the lower
actinicity of this light. The necessity of the use of such a selec-
tive method of reducing the glare from these lamps by absorbing
a portion of the non-actinic rays is emphasized in the moving
picture production studio. The illumination necessary is enor-
mous and if multiplied several times (as is the case when the
clear tungsten lamp is used) becomes very annoying especially
in the large sets.
As already mentioned portability of the lighting apparatus is
I/O TRANSACTIONS I. E. S. — PART I
quite desirable. The mercury arcs are usually arranged in ver-
tical banks of eight each in a frame supported on wheels. The
carbon arc lamps are usually non-portable with the exception of
the bare high-amperage arcs which are placed on tripods. A
form of portable standard developed in one of the studios using
the special blue-bulb gas-filled tungsten lamps is shown in Fig. 15.
The stand is made to be adjustable for height and the lamps may
be tilted about their supporting arms. One of the white-
enamelled angle steel reflectors shown in Fig. 12 was adopted
and found satisfactory. It has also been recommended in one
studio using the scheme of permanent installation that the blue-
bulb gas-filled tungsten lamps be used in series with a rheostat
which would reduce the voltage of the lamps below normal. Only
while the camera is being operated would the rheostat be cut out.
thus subjecting the lamps to about 10 per cent, over- voltage.
This would reduce the number of lamps necessary and if care
were exercised the decrease in life of the lamp would not be
serious.
To summarize the requirements in artificial lighting of moving
picture production studios, the characteristics of the light sources
placed in their order of importance are as follows : high actinic
value of the radiation, portability, control of the light, color- value
of the light, energy consumption. In most cases energy consump-
tion was found to be a minor consideration.
The author desires to acknowledge his indebtedness to Mr.
H. McMullan for his assistance in the experimental work and
for the preparation of the illustrations.
DISCUSSION.
Mr. Wm. A. D. Evans (Communicated) : There are one or
two points brought out in Mr. Luckiesh's article which are not
entirely clear to me, and there are also two or three items, re-
garding which I am not in entire accord with his views.
On the second page Mr. Luckiesh makes the following state-
ment :
The spectrum of the mercury arc, being a line spectrum, is not
plotted, but its actinic value for ordinary plates is much more nearly that
of daylight than that of the new tungsten lamp. In some respects, it is
not as desirable as the latter for photographic purposes.
NEW HIGH-EFFICIENCY LAMP I/I
I cannot conceive in any respect whatsoever that the mercury-
vapor lamp is not as desirable as the nitrogen-filled lamps for
photographic purposes. A lamp to be desirable for photographic
purposes should be rich in the so-called "actinic rays." And as
Mr. Luckiesh has stated that the actinic value of the spectrum
of the mercury-vapor lamp is nearly equal to that of daylight, it
would seem that its desirability for photographic purposes could
not be added to.
On page 4, it is stated :
It is seen that for an ordinary photographic plate the light from a
mercury arc is three or four times more actinic than the light from the
gas-filled tungsten lamp operating at 20 lumens per watt. Owing to the
compactness of the light source of the tungsten lamp, however, the light
is more efficiently controlled or directed than in the case of an extended
source. This tends to overcome the disadvantage of the gas-filled tungsten
lamp with its lower actinic value per lumen.
In relation to this, I note further on that Mr. Luckiesh states, on
the fifth page, that "a 1,000-watt, gas filled tungsten lamp oper-
ating normally at 115 volts and 18 lumens per watt." Under
ordinary operating conditions, is the nitrogen-lamp operated at
18 lumens per watt; whereas, in comparative tests against mer-
cury arcs, is the lamp operated at 20 lumens per watt?
Regarding the "extended light source" I desire to say that the
average photographer is accustomed to natural light coming from
a skylight for his work, which is nothing more or less than an
extended light source and the question of diffusion is most im-
portant for proper photography. As far as possible, photo-
graphers desire to get away altogether from the so-called "spot-
lighting" effects. It might be advisable in some cases to use a
spot-light to bring out certain high lights, etc., but the main
lighting is always desired from an extended source. I fail to
see how in this case the gas-filled lamps by being more efficiently
controlled can overcome the disadvantage of its lower actinic
value per lumen.
On page 13 the statement is made that:
The green line (0.546 mu) and the yellow lines (0.577 and 0.579 mu)
to which 95 per cent, of the visible light must be credited do not show
on the reproductions which are made from ordinary plates.
From investigations made by Messrs. Fabry, Lardenburg, Von
1/2 TRANSACTIONS I. E. S. — PART I
Recklinghausen, Henri, Coblenz, and others showing the relative
intensity of the four visible lines in the mercury spectrum, oper-
ating in a low pressure lamp or glass tube lamp, the green and
yellow lines (0.546 mu and 0.577-9 mu) are responsible for
practically 75 per cent, of the light in place of 95 per cent., as
stated by Mr. Luckiesh.
In this connection, it might be stated that a very curious co-
incidence occurs in the mercury lamp. Of the four lines which
are prominent in the visible spectrum, the line 546, which is
present, is located at the point of maximum sensibility of the
eye; while the line 404 is located approximately at the point of
maximum sensibility for the photographic plate.
On page 12 Mr. Luckiesh shows a photograph of a photo-
reproducing machine lighted by four 1,000-watt nitrogen lamps.
In ordinary practise, throughout the country, this work has been
accomplished by two 385-watt mercury-vapor lamps, which
shows a ratio of approximately one to five in the amount of energy
consumption for the same class of work.
On page 19 it is stated:
Regarding the speed at which portraits can be made with the special
photographic lamp, it is sufficient to state that the exposures are the
same for daylight. This is not true with the clear lamp because it is
impossible to obtain sufficient actinic value to insure success with short
exposures without producing a condition of glare which is not conducive
to the production of satisfactory pictures, unless excessive over-voltage
is applied.
From reading this, it would see as if the author meant that with
the blue glass lamp added actinic value was secured, that is, an
ordinary clear lamp could have its actinic value increased simply
by putting on the blue glass. I do not think he meant to convey
this idea, but this is the impression which would be gathered.
In relation to the lighting of motion picture studios I desire to
state that most of the data submitted by Mr. Luckiesh is for
small work. For one of the largest indoor stages in the country
the lighting installation consists of 17 banks of eight mercury
lamps each, hung overhead and about 8 ft. from the floor at the
front line and gradually rising at about on angle of 30 degrees,
so that the back lamps are about 20 ft. from the floor. Two
banks are placed in front, and the number gradually widening
NEW HIGH-EFFICIENCY LAMP 1J$
out going towards the back. Along one side are also hung five
banks at an angle of about 45 degrees to throw the light in on
the side. These lamps are all mounted overhead on trolleys, and
can be moved lengthwise of the studio, so that the scene can be
set up on any one of three stages. In addition, there are pro-
vided six floor stands of eight lamps each, which are used on one
side of the stage and down towards the front, practically all the
light coming from overhead and one side, there being, as might
be said, a complete curtain of light across the ceiling and down
on the side. This stage allows the setting up of scenes 32 ft. deep,
with a back line of 24 ft., and a front line of 8 ft., and approxi-
mately with an average intensity of about 300 to 350 foot-
candles.
Furthermore, with this mass of lamps lighted, there is practi-
cally no glare to bother the actors and the heat is in no way
excessive and hardly noticeable.
In summarizing the requirements of the artificial lighting of
motion picture studios, the author places the characteristics of
light sources in the following order : the high actinic value of the
illuminant, the portability and control of the light, the color value
and the energy consumption. He states in most cases the energy
consumption was found to be a minor consideration. This has
not always been the writer's experience, as energy consumption
is quite a vital fact in a large studio, which is being operated all
day and is a point which has to be taken into consideration.
Moreover, another point which the author neglected to men-
tion, and which is very important — that is the maintenance. This
is a feature which I believe is as important in motion picture
studio work, as in any other commercial industry.
Dr. C. E. K. Mees (Communicated) : The advent of the new
high-efficiency tungsten lamp was naturally of the very greatest
importance to those interested in the development of photography,
inasmuch as it not only placed at their disposal with artificial
light a high-intensity source, but that source differed from the
former high-intensity sources in the fact that it was especially
rich in red and green rays.
The importance of this is derived from the fact that the
tendency of photography is towards the effect of color correct
1^4 TRANSACTIONS I. E. S. — PART I
methods, and eventually of color photography. Whereas the
older photographic materials were sensitive only to the shorter
wave-lengths, within the last few years there have been intro-
duced materials sensitive to the whole visible spectrum and
radically different from the earlier orthochromatic plates, which
were sensitive only to the blue and violet and to a small region
of the yellow-green of the spectrum. These panchromatic plates
are of comparatively recent introduction, and while they are
largely used for special work requiring sensitiveness to red and
green, such as color photography or commercial work involving
the photography of red and yellow objects, their use in por-
traiture is rapidly increasing, though it is, at present, very lim-
ited, the professional photographer preferring to use the more
easily manipulated and cheaper materials to which he has hitherto
been accustomed. The advantages of panchromatic plates for
portraiture, however, are manifest. The human skin is covered
with small capillaries of a red color, producing streaks and
blotches of light red, which, while nearly invisible to the eye,
have a very strong absorption for violet light, so much so that
under a light source which transmits no red the skin is seen to be
of a very uneven texture, and this uneven texture is reproduced
in photographs taken on materials sensitive only to the shorter
wave-lengths, so that portrait negatives exaggerate skin defects,
and invariably are worked up by hand in the retouching process.
Retouching is used partly to correct defects in lighting, and
partly to enhance the beauty of the sitter, but the greater portion
of the work done is to improve the surface of the skin, and it
is this work which has caused retouching to be reproached with
the spoiling of the likeness.
From this it will be seen that the use of panchromatic plates
is by no means likely to be confined to the few kinds of photo-
graphic work where they have hitherto been considered essential,
because there is, in fact, little photographic work where correct
color rendering is not an advantage, and in portraiture, which
represents the widest field of all, the advantage is so great that
red sensitive plates would probably have been used long ago but
for the difficulties which attend their use. Of these difficulties
the greatest has been the greater exposure which has been neces-
NEW HIGH-EFFICIENCY LAMP 175
sary in order to get correct color rendering. Even with the best
color sensitizers, the sensitiveness to red and green which can be
obtained is much less than its sensitiveness to blue light when
tested on a daylight spectrum, and consequently in order to get
satisfactory color rendering, yellow niters have to be used with
the plate, which considerably increases the exposure.
It is not true that orthochromatic or panchromatic plates are
much slower in their total sensitiveness than non-color sensitive
plates, but even with the best panchromatic plates an increase of
exposure of about three and a half times is necessary for day-
light with the lightest filter which will give correct rendering, and
this increasing exposure has greatly militated against the applica-
tion of the plate to portraiture.
When we turn to the employment of artificial light sources,
however, we are faced with quite different conditions. Artificial
light sources are so rich in red and green rays that only a very
light filter — if, indeed, a filter at all — is required for the use of
panchromatic plates, while the multiplying factor of this filter is
reduced by the excess of red and green in the light source, so that
a panchromatic plate, with such a source of light as the nitrogen
tungsten lamp, requires less exposure than the corresponding
plate unsensitized, while, of course, the color rendering is quite
satisfactory. The introduction of the nitrogen tungsten lamp,
therefore, marks an era in artificial lighting for studio work as
it does in almost all other branches of the lighting art.
With the introduction of this lamp photographers all over the
world commenced experiments which were marked with great
success, and there is no doubt that the nitrogen tungsten lamp is
destined to be one of the chief illuminants for studio portraiture
in the future, and indeed I, personally, am inclined to think that
studios lighted in this manner will to some extent displace day-
light studios. With the introduction of this illuminant the possi-
bility of obtaining correct color rendering in color portraiture is
very greatly increased, and although at first the tungsten lamps
would be used with ordinary plates, the use of panchromatic
plates will undoubtedly grow, and we may expect consequently
that indirectly the tungsten lamp will aid in the production of
176 TRANSACTIONS I. E. S. — PART I
more correct portraiture, giving a more faithful rendering of the
skin texture than has been possible in the past.
Turning to the new lamp of blue glass, this lamp, while
undoubtedly of a pleasing color to the eye, abandons the very
advantages of excess of red and green which are such valuable
factors in the tungsten lamp when used with color sensitive
materials, and it will, therefore, clearly not be of use for this
purpose. At the same time, most studios do not and will not for
some time use such color sensitive materials, and, therefore, the
loss of the red and green in the blue glass lamp is of no impor-
tance photographically, and the loss of the blue light being small
(though it is by no means negligible) the diminution of glare
and the more pleasing color would entirely justify the adoption
of the screen lamp.
The great advantage of this lamp is that it can be used to rein-
force lighting either by daylight or by the enclosed arc where the
unscreened lamp on account of its color would be objectionable
as introducing two different colors in the lighting, and for this
purpose the new lamp will undoubtedly be in considerable de-
mand. Thus, it seems to me that both the unscreened and
screened lamps represent an advance in photographic portraiture
— a screened lamp as a reinforcing lamp for daylight, and an
unscreened lamp as assisting the introduction of materials giving
correct color reproduction — which must tend to the general
improvement of the status of photography.
When we turn to cinematographic work, however, it seems a
little doubtful whether tungsten lamps will be employed to the
same extent for black and white cinematographic work, though
they represent an invaluable aid in the experimental work on
color cinematography, on which so much is being done. An
investigation of the gradation of non-color sensitive materials
such as those used for the negative film in moving picture work-
shows that the gradation improves as we pass towards the more
infrangible end of the spectrum, so that a film which gives very
excellent gradation at 400/i/i, will give by no means as good results
for a light with a mean wave-length of 480/x/*, and if comparative
photographs are taken by these two wave-lengths, it will be found
that in the photograph taken by the longer wave-length the high-
NEW HIGH-EFFICIENCY EAMP \yy
lights are clogged up and deficient in detail and very easily show
strong halation, while in the photograph taken by shorter wave-
lengths the highlights will retain all their quality, and owing to
the opacity of the film for light of this wave-length halation will
be nearly absent. For this reason it is improbable that in cine-
matographic work the nitrogen tungsten lamp will displace the
illuminants at present used ; namely, the mercury- vapor lamp and
the enclosed arc lamp.
If cinematographic pictures be taken by mercury- vapor lamps
and also by nitrogen tungsten lamps, the difference in the quality
of the pictures will be most marked, the highlight gradation being
well retained in those taken by the mercury lamp and the absence
of halation being noticeable, while in those taken by the nitrogen
tungsten lamp the highlights are clogged up and halation appears
wherever any portion of the picture has been over-exposed. This
effect is undoubtedly due to the difference in the color of the two
light sources. If the spectra of the two light sources be pho-
tographed by non-color sensitive materials, it will be seen that
the center of action of the nitrogen tungsten lamp is at 480^,
while a fair average of the lines of the mercury-vapor lamp
would place its center of action at about 400, the lines at 365, 404
and 436 being all of nearly equal density.
A small practical advantage of the mercury- vapor lamp is that
it is a light source of considerable area and of low visual intensity,
so that the lamps can be used without any diffusing screen, and
if long tubes are used widely spaced, a set of mercury-vapor
lamps makes an effective substitute for a window.
When we turn to the question of efficiency, we also find that
although the nitrogen tungsten lamp is of high efficiency for the
visible spectrum, it is much surpassed by the mercury-vapor lamp
and the enclosed arc lamp in the violet and ultra-violet regions of
the spectrum, and this is an additional reason for the use of these
latter lamps in moving picture studios, where efficiency is of
high importance.
Summarizing the views expressed in this paper, therefore, we
may say that in ideal photography materials should be used which
will render color values as they are seen by the eye, and that
the introduction of the nitrogen tungsten lamp renders the use
1/8 TRANSACTIONS I. E. S. — PART I
of such materials for studio work easy and is to be welcomed
for this reason. For studio work where non-color sensitive
materials are to be used, and especially where a light acts as a
supplement to daylight, or the enclosed arc lamp is required, the
blue glass nitrogen tungsten lamp will be of great use. For
moving picture work, however, both conditions of efficiency and
of the quality of the resulting negatives are likely to tend towards
the continuance of the light sources at present in use, and to pre-
vent their replacement to any appreciable extent by the nitrogen
tungsten lamp.
Prof. George A. Hoadley : Mr. Luckiesh has shown us in
the curves on the third page (Fig. 2) the difference in sen-
sitiveness, between the eye and the photographic plate. Now
take a point source of light, and let a ray from it strike upon
a lens, of which we may consider this a half cross-section. We
know that when the ray strikes the lens, we have a bending of
the rav. We also know that if it is white light when it strikes the
lens, the ray will not only bend, but will be dispersed, and we
shall probably have it coming down in this direction — we have
the red at R (Fig. A) and the violet nearer the lens at V, and
consequently we have a horizontal spectrum from the red to the
violet — between those two points. Now this becomes of value
when you consider that we shall have a red focus at R and a
violet focus at V. The eye will focus better in the position
marked Y; the photographic plate in position V. We have
pretty nearly that condition in astronomical photography. We
are looking at point sources in the location of thousands of
stars, and if we focus our apparatus and put the plate at Y, we
shall find that the time of exposure will have to be very much
longer than if we should put the plate near V at the actinic
focus. Consequently in a larger lens it is necessary to make
that distinction, or that difference in the position of the plate,
in order to take the picture more quickly, and in order to get a
NEW HIGH-EFFICIENCY LAMP 1 79
better focus. With the ordinary camera lens that is not necessary
at all perhaps on account of the fact that we get rid of the dif-
ference in focus by many different kinds of glass and a com-
bination of lenses.
Mr. M. LuckiESh (Reply to Mr. Evans) : In regard to Mr.
Evans' first quotation from the second page of my paper will
state that the actinic value of the mercury arc, while nearer to
that of daylight for ordinary plate, need not be sufficient to stamp
the mercury arc as good as tungsten light for all photographic
work. Mr. Evans cannot conceive this so I will refer him to
the proper rendering of color values as one instance where the
mercury arc fails.
Mr. Evans next quotes from the fourth page of my paper re-
garding the operating efficiency of the tungsten lamps used. I
designated in each experiment the efficiency at which the lamp
was operating. I am merely interested in presenting facts.
Further the efficiency of operation is subject to change from
month to month as there is always the tendency toward higher
luminous efficiency in the electric incandescent lamp industry.
There is no point in the least to Mr. Evans remarks on that
score. I used different lamps at different times and for the sake
of exactness expressed the conditions exactly.
He further takes issue with my statement that the light from
the small source (the incandescent filament) is more efficiently
controlled than from an extended source. I believe Mr. Evans
at any other time will agree to this. He misconstrues my mean-
ing for I do not recommend spot light effects in the studio. His
conception will be clearer when I remind him that in the moving
picture studios is this exemplified. In a mercury arc installation
much of the light is not directed upon the objects to be photo-
graphed but wanders away never to return.
He further quotes from the thirteenth page and takes issue
with my statement that 95 per cent, of the light from the or-
dinary mercury arc which I used must be credited to green and
yellow lines. He quotes others as obtaining different results.
I must remind Mr. Evans that the problem of color photometry
has not yet been solved, so various persons will obtain different
results depending upon the method used. I quoted data ob-
4
l8o TRANSACTIONS I. E. S. — PART I
tained by myself by the direct comparison method of photometry
after considerable investigation of methods of color photometry.
I used as an illustration a photostat equipped with four 1,000-
watt tungsten lamps and Mr. Evans states that the same work
is done with two 385-watt mercury-vapor lamps. His citation
lacks value, however, inasmuch as he neglects to give compara-
tive speed. Various wattages are being used for such equipment,
but I took this photograph merely as an illustration for high
speed work. Mr. Evans appreciates that the necessary factor —
exposure — has been omitted by him in his comparison.
Mr. Evans quotes from the nineteenth page and thinks that
the impression gained is that the blue lamp adds actinic value.
The portion of the paper devoted to the modified bulb is devoted
practically entirely to data showing that I have eliminated rays
of practically no photographic value for ordinary plates.
In regard to the lighting of moving picture studios by means
of tungsten lamps I submitted only the data available at that
time. I am sorry that I was only able to cite smaller studios,
but the work has just begun. The outlook is promising and I
will try to present much more data regarding this field at some
future time.
Mr. M. Luckiesh (Reply to Dr. Mees) : Regarding the future
of the tungsten lamp in cinematographic work we can only con-
jecture. It is being used to-day in some of the smaller studios
with entire satisfaction. Certainly it will find a place of more
or less importance in such work. I quite agree with Dr. Mees
that we should photograph with an object of rendering true
color-values as they are seen by the eye. But at present this is
being done only to a relatively small extent in the portrait studios.
It was for this reason (and others) that I have recommended
and developed the blue bulb lamp giving a rough "photographic
daylight." Dr. Mees, however, shows that there are exceptions
when he claims that the illuminants at present used in cine-
matographic work have an advantage over the clear tungsten
lamp because the light of longer zvave-lengths is present in lesser
amounts in the former light sources.
luckiesh: safeguarding the eyesight 181
SAFEGUARDING THE EYESIGHT OF SCHOOL
CHILDREN*
BY M. LUCKIESH.
Synopsis: The object of this paper is to present to school authorities
the importance of proper lighting in safeguarding the eyesight of school
children. Data are presented showing the increasing prevalence of near-
sightedness with advancing school grades and other data showing the
decrease in the percentage of shortsightedness accounted for in part at
least to the improvement in lighting conditions. Opinions of authorities
are quoted which show the importance of good lighting in preserving
eyesight and the economic gain in such conservation. Factors which
influence vision are discussed; namely, illumination, uniformity, direction
of light, glare, character of reflecting surfaces, etc. Legislation on school
lighting is discussed. Extracts from enacted laws pertaining to the
subject and general recommendations for school lighting legislation are
presented. Satisfactory and unsatisfactory conditions found in modern
schools are illustrated and the co-operation of school authorities in
improving lighting conditions is urged. A partial bibliography of the
literature pertaining to school lighting is appended.
INTRODUCTION.
There are twenty million school children in the United States
who are devoting several hours each day to study or perform-
ance of other work equally trying on the eyes. According to
the available statistics about 10 per cent, of the number of school
children examined are found to have defective vision. In many
cases the percentage of defectives has been found to increase
with increasing age. This increase can be attributed largely to
the manner in which the eyes are used. Light being essential to
vision, it is natural to turn to lighting for a possible cause of the
increase in the number of children with defective vision. Con-
sidering those that are already defective it is certain that proper
lighting and proper use of the eyes will result in a large number
being permanently cured. Further, this is an age of prevention
as well as cure. Prevention of defective eyesight means proper
lighting and proper use of the eyes. It should be remembered
that the child's eyes are immature in growth and function and
therefore quite susceptible to misuse. Insufficient illumination
whether due to shadows owing to improper direction of light or
* A paper read at a meeting of the Pittsburgh Section of the Illuminating Engi-
neering Society, Cleveland, Ohio, January 29, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
182
TRANSACTIONS I. E. S. — PART I
to an actual deficiency in the amount of light at a particular
desk results in the tendency of the child to hold the reading
matter too close to his eyes. Practising this continually, results
in a malformation of the eye muscles and consequent near-sight-
edness. The tendency once begun requires more effort to correct
than to prevent beforehand.
Glare from windows, blackboards, glazed paper or artificial
light sources causes eye-fatigue with resulting disorders too com-
plicated to discuss in a paper of this nature. A lack of training
in avoiding such conditions also aids in increasing the number of
children having: defective vision.
Fig. i. — Prevalence of short-sightedness in three secondary schools
in Stockholm, 1894-1903.
Prof. Johan Widmark of Sweden in a paper on "The Decrease
of Short-sightedness in Secondary Schools for Boys in Sweden,"
presented at the Fourth International Congress on School Hy-
giene held in Buffalo in 191 3, publishes some interesting statistics
Some of these have been plotted and are shown in Figs. 1 and 2.
In Fig. 1 are shown the data gathered in three kinds of schools.
These illustrate the increase in near-sightedness with increasing
grade of class. The classes are named first, second, third,
fourth, fifth, lower sixth, upper sixth, lower seventh, and upper
LUCKIESH : SAFEGUARDING THE EYESIGHT
183
seventh. The corresponding percentage of near-sighted pupils is
shown for each class. The most striking feature is the unques-
tionable increase of near-sightedness from class to class. A
further point of interest being the greater prevalence of near-
sightedness in the "classical" school than in the "modern" school.
Another school which has both the classical and modern side has
in general a slightly less percentage of near-sighted pupils than
found in the classical school.
Tv'T'.v-'i-vy^.-r.rr
Md-W^\H::tm:n^^
f /9oo /
Year-
Fig. 2. — Percentage of short-sightedness in the highest class of all
the state secondary schools for boys in Sweden.
In Fig. 2 is shown the steady decrease in the percentage of
short-sightedness in the highest classes of all the state secondary
schools for boys in Sweden from 1895 to 1906. Data obtained
in 1883 but perhaps not directly comparable with the foregoing
data showed a percentage of near-sightedness as high as 65 per
cent, in some schools. Prof. Widmark accounts for the decrease
in short-sightedness in recent years as illustrated in Fig. 2 as
follows :
Among the hygienic improvements which have been effected during
recent years in our schools and in all the conditions relating thereto I
should be disposed to mention first the improvements in the lighting of
rooms and in the printing of the books used by pupils, and that for this
reason among others, that the influence of these changes is of effect in
184 TRANSACTIONS I. E. S. — PART I
the homes too, the strain on the eyes when the pupils are busy with the
preparation of lessons being thereby much reduced. If the comparison is
made between the methods of lighting rooms now and those of ten years
ago, the difference is very striking, both at school and at home.
He further comments upon the significance of the decreased
use of the old Gothic types.
Opinions of Other Authorities. — At the Buffalo meeting on
School Hygiene conservation of vision received marked atten-
tion as is illustrated by the following abstracts :
D. P. MacMillan, director of child study in the public schools
of Chicago, states :
Defects of the senses of sight and hearing, to which appeal is largely
made in school room activities, are considered by some to be the primary
causes of delay or derangement of normal development, and they lead to
the formation of injurious habits, etc.
W. H. Brainerd, an architect of Boston, states in discussing
"The Ideal School Site":
The first purpose of the school is instruction. The first need of
instruction rooms is light for the use of the eyes and apparatus. Light
must be in abundance and without glare. Sunlight should reach all
instruction rooms, and others as far as possible. Long continued hot sun-
light is not desirable in class-rooms. The desirability of exposure for
class-rooms is in the following order : easterly, southerly, westerly. For
large buildings a site permitting of the major axis running northeast and
southwest is most desirable. Class-rooms should have the easterly and
southerly exposures ; assembly halls and accessories westerly and northerly
exposures.
Dr. F. Park Lewis of Buffalo in a paper on "Sight Saving and
Brain Saving," states :
It is an accepted fact, recognized by ophthalmologists everywhere,
that changes occur in the eyes of children during the period of their
school life, of which the most prominent symptom is a steadily progressive
development of near-sightedness. As definitely formulated by the late
Prof. Dufour: (1) In all schools the number of short-sighted pupils
increases from class to class. (2) The average degree of short-sighted-
ness increases from class to class. (3) The number of short-sighted
pupils increases with the increase in school demands.
Dr. James Kerr of London, states :
Ocular experience is the only final test of illumination. Eyestrain is
due to fatigue due to overwork or glare. The eye adapts itself to bright-
ness by varying its sensitiveness. Primary glare is due to physical effects
on the retina, secondary glare to difficulty in adaptation. One third of
our school children have such defective visual acuity that better illumina-
tion is necessary than for normal eyes.
LUCKIESH : SAFEGUARDING THE EYESIGHT 185
He further states that
Artificial lighting for each school place should not be less than 2
foot-candles. Blackboards require 60 per cent. more. Glare must be
guarded against.
Dr. Lewis C. Wessels of the Bureau of Health, Philadelphia,
in speaking of defective vision from the economic standpoint
states :
In Philadelphia each pupil costs about $35 per year to teach. Under
normal conditions a pupil 14 years of age should reach the eighth grade
at a cost to the state of $280. If on account of defective vision the child
only reaches the fourth grade in that time it has still cost the state $280,
but with only $140 worth of result, a loss to the State of $140. The loss
to the child is considerably more because at the age of 14 it is likely to be
put to work, poorly equipped, its earning power curtailed for want of a
proper education so that it can contribute but little toward its own support
or that of the state. So again the state loses.
He further explains how the Department of Public Health
through a division of ophthalmology furnishes glasses free to
poor children and adds
We are now refracting nearly 2,500 cases a year. If we save each
one of these children but one year during its entire school life there will
be an annual saving of over $87,000 not counting the child's time and
increased efficiency.
This is certainly an interesting phase of the subject. A further
discussion of the economics of the relative costs of prevention
and cure would also be of interest.
These are opinions and statistics from only a few authorities
but probably sufficient to rout any lurking suspicion that the
safeguarding of eyesight is not a vital problem. Further it is
seen that the light expert has a great deal in common with school
authorities, medical examiners, and architects in safeguarding
the most important and educative sense — vision.
FACTORS INFLUENCING VISION.
Illumination.— The eye is a very flexible organ and can adapt
itself to a tremendous range of brightness. Visual acuity or the
ability to distinguish fine detail depends upon the illumination,
although above a certain minimum value of illumination acuity
increases very slowly with increasing illumination. One sees by
distinguishing differences in brightness and color. In ordinary
reading brightness contrast makes it possible to distinguish the
1 86 TRANSACTIONS I. E. S. — PART I
black letters or words on the lighter background. After a cer-
tain minimum value of illumination is reached the process of
distinguishing ordinary type becomes increasingly difficult with
decreasing illumination. The amount of illumination necessary
for reading with comfort depends upon a number of conditions,
but under fairly satisfactory conditions the illumination at the
top of any desk should not be less than 2.5 foot-candles. This
minimum value should be greater for daylight than for artificial
lighting because of the greater non-uniformity of the illumina-
tion under average natural lighting conditions indoors.
Uniformity.- — A fair degree of uniformity of illumination on
the plane of the desk tops is quite desirable owing to the strain
on the eyes resulting from the necessity of adapting the eyes for
considerable variations in brightness where there is too great
non-uniformity. Owing to architectural difficulties it is quite
impossible to obtain uniform illumination with natural light.
The diversity, however, can be reduced even in this case to a
satisfactory value. Satisfactory uniformity is easily attainable
in artificial lighting.
Direction of Light. — One of the fundamental principles of
proper lighting is to have light come from the left. This of
course assumes that all persons are right-handed. In natural
lighting three systems are in vogue, unilateral, bilateral and sky-
lighting. The predominant opinion favors unilateral lighting
with the windows on the left of the pupils when seated.
In artificial lighting there are three general systems of lighting.
the so-called direct, semi-indirect, and indirect lighting. These
divisions are not clearly defined. The first system in which most
of the light is directed downward by shades and reflectors is per-
haps used more than the others although the semi-indirect
method is growing in popularity in many places and is perhaps
more generally satisfactory in the problems of lighting class
rooms, reading rooms, etc. In this system the light source is
contained in a translucent glass bowl open at the top. Some
light passes through the bowl to the working plane, the remainder
reaching the working plane indirectly by reflection, chiefly from
the ceiling.
Glare. — In natural lighting the sky is the source of light
LUCKIESH : SAFEGUARDING THE EYESIGHT
l87
chiefly depended upon. Very elaborate studies of the amount of
visible sky necessary at any point of the room have been made by
reflection chiefly from the ceiling. Various authorities agree in
general, notwithstanding the fact that the data have been gathered
by different methods. The brightness of the light source whether
natural or artificial, should be low, say not more than three
candlepower per square inch. The brightest sky measured by
the writer has shown 2.5 candlepower per square inch. One of
the important effects of high brightness is the production of
annoying after-images. In Fig. 3 are shown some results on the
£zz^>a34/r& /rr CSe-casrt/j
Fig. 3.— Effects of brightness of source and exposure on the duration
of the after-image.
duration of after-images. The brightness of a tungsten filament
operating at 7.9 lumens per watt (1.25 w. p. m. h. c.) was found
to be 1,080 candlepower per square inch. In the same units the
approximate brightnesses of a Welsbach mantle and a frosted
tungsten lamp of the older type are respectively 30 and 5. These
figures are given to aid in comprehending the data. The after-
images actually lasted longer than shown in Fig. 3, but at the
end of the intervals of times indicated they ceased to be annoy-
ing and changed color which latter served as a criterion in
making the observations. It is seen that the after-images from
1 88 TRANSACTIONS I. E. S. — PART I
bare artificial light sources besides fatiguing and being harmful to
the eye can be annoying owing to loss of time occasioned and dan-
gerous when the person is working near machinery owing to the
temporary blinding effect. Nevertheless inspection shows that
bare lamps directly in the field of view are often found in the
shops in technical schools where there is an ever-present danger
from machinery in operation.
Intrinsic brightness is not alone the cause of glare. An area
of sky when viewed through a window surrounded by relatively
dark walls causes a very annoying glare yet the sky is perhaps no
brighter than i candlepower per square inch. Thus excessive
brightness contrasts are found to be responsible for the annoying,
and sometimes very discomforting and harmful conditions of
glare. This is shown by an easy experiment. Hold a lighted
electric incandescent lamp before your eyes in an ordinary room
and under most conditions you will experience uncomfortable
glare. However, if you take the lighted lamp to the window
and view it against the sky the glare is hardly noticeable. There
is another factor which complicates the situation namely total
light flux. More light is entering the eye in the latter case which
possibly by the process of adaptation reduces the annoyance
somewhat. It has become recognized, however, that brightness
contrast plays a large part in eye- fatigue. A blackboard viewed
in juxtaposition to a white wall often results in annoying glare.
Light surroundings such as walls and ceiling have a general
tendency in reducing the conditions of glare. For instance a
bright ceiling reduces the annoyance of an artificial light source
viewed against it. Light walls reflect light back to the side of the
room containing windows thus lessening the contrast between the
bright sky and the adjacent walls. The colors of walls and
ceilings usually found satisfactory are light tints of buff, yellow,
or grey.
Artificial light sources should be hung high in order to be out-
side the normal visual field if possible. They should be
screened with shades or reduced in brightness by enclosing glass-
ware. Likewise windows should be equipped with approved
shades in order to control the daylight as much as possible and,
when necessary, to screen out the direct sunlight.
LUCKIKSH : SAFEGUARDING THE EYESIGHT
189
Polished surfaces are recognized as sources of annoying glare
and in many cases defeat well laid plans of the lighting special-
ist. In Fig. 4 the various kinds of reflecting surfaces are il-
lustrated; a shows mirror reflection, and b the reflection from a
perfectly mat surface; c shows a combination of these which
results from a highly glazed white surface, for example varnished
white walls and glossy paper. A piece of polished window glass
placed over white blotting paper is a simple illustration of this
kind of reflection ; d and e illustrate two other types of reflection
encountered.
Obviously a child holding a mirror flat upon the printed page
of a book can see the image of a light source which is well above
6
6
<?> 6
<§>
Fig. 4. — Various types of reflection.
his head out of the normal visual field. The result of glazed
paper too often used in books is somewhat analogous. Owing to
the fact that the image of the light source is regularly reflected by
the black letters and white background with practically equal
facility, there is a decrease in contrast between the printed
matter and the background causing difficulty in reading and also
a distracting and harmful effect of the "glare spot." For these
reasons glazed surfaces have been condemned by the light spec-
ialist. Glare owing to regular reflection from blackboards is a
common annoyance in school rooms. This can be overcome in
various ways including tilting, the judicious use of window
shades, and by lighting them artificially. The proper placing of
blackboards can be determined beforehand as illustrated in
Fig. 5 ; a shows a plan of a class room lighted from one side.
190 TRANSACTIONS I. E. S. — PART I
In this case the lighting is from the wrong side, but this was
chosen because it represents an actual case. The paths of the
rays of light can be followed in their course with the result that
the condition shown is just what was observed in the room in
question. In b is shown the elevation. In this case the window
area was too small and a further mistake was made in placing a
blackboard between the windows. These are conditions that can
not be too severely condemned. In c is shown a remedy for badly
lighted blackboards. Walls and desk tops should also be as free
from glaze as practicable.
Considerable data have been obtained on the effect of glare in
reducing visual acuity, much of which will be found in references
cited in the bibliography. However, an interesting case is shown
in Fig. 6 because it brings out various points of interest and also
incriminates the sky in glare production. An acuity object was
set up in the shade of a building as far from the building as pos-
sible. The day was clear and light reached the object from more
than one half of the sky. No light from the sun reached the eye
or test object or immediate surroundings directly or by regular
reflection. The writer who made the observations wore no visor
to shield the eyes. Only a slight sensation of glare was apparent
before beginning the test. However, as soon as acuity observa-
tions were begun the glare became very evident and rapidly grew
painful. Five readings were made first through clear correcting
glasses (represented by the black dots). As quickly as possible
the clear glasses were replaced by yellow-green glasses of about
50 per cent, transmission for the total light and five acuity read-
ings were taken (represented by crosses). A decided decrease
in discomfort was experienced when wearing the yellow-green
glasses and as will be noted acuity is higher in this case notwith-
standing the decrease in illumination was fully 50 per cent.
These glasses were again replaced by clear glasses and five acuity
readings were made. This procedure was continued as indicated
in Fig. 6. The interval of time required to make five readings
including the change of glasses was the same in each case (being
three minutes), but the actual time of taking the individual read-
ings was not noted. Here they are plotted at equal intervals.
While the above procedure is rather complex and bears upon
EUCKIESH : SAFEGUARDING THE EYESIGHT
I9I
A,
y
c
^
X
\3'
PLAN
a
Fig. 5. — Showing law of regular reflection applied to blackboards.
192
TRANSACTIONS I. E. S. — PART I
problems worthy of much careful investigation, the experiment
answered the intended purpose in bringing forth several points:
(1) Glare conditions are not always apparent when the eyes are
not engaged in serious work such as reading or distinguishing
fine detail. However, bad lighting conditions are readily recog-
nized when the eyes are called upon to do such work. (2) There
is a rapid falling off of visual acuity when the conditions of glare
are severe. (3) Such a harmless appearing light source as a wide
expanse of sky can produce a very severe condition of glare. The
intrinsic brightness is very low as compared with artificial sources,
but the quantity of light is high and the image of the sky is spread
over a large portion of the retina. (4) There was an apparent
recuperation of the eye during the periods that the yellow-green
/*
»
\ .6
\
•
i
•
r-*-*-*_2_
X
L m -
rTT
« W.a'.n^ <rllwjr«n 5U1
se>. SO*/. t<»i»mi«.'on
e
—
• WtaK-.n^ clear jl>ISM.
-
0
1
6 9 /*.
Fig. 6. — Showing rapid reduction in visual acuity under the glare
from the unobstructed blue sky.
glasses were worn. (5) Notwithstanding the effect of glare,
when clear glasses were worn, in reducing visual acuity the values
of the latter when the colored glasses were worn remained con-
siderably higher. (6) This experiment emphasizes the necessity
of prolonging acuity readings over a considerable period if
acuity is to be a criterion of the satisfactoriness of illumination
conditions.
Some of the increase in visual acuity when the yellow-green
glasses were being worn can be accounted for by the nearer
approach to monochromatism of the light that passed through
them. However, conditions indicated that the advantage was due
very largely to a reduction in the glare. Other interesting con-
clusions can be drawn, but the illustration has already fulfilled its
luckiesh: safeguarding the eyesight 193
object in bringing forth the facts that glare conditions are very
complex and that cognizance of glare often depends upon the
character of the activities in which the eyes are engaged.
LEGISLATION ON SCHOOL LIGHTING.
The legislation on this subject which has come under the obser-
vation of the author has been chiefly with reference to natural
lighting. This is quite the expected course, but needless to say
attention must be given to artificial lighting. The latter problem
will be found much easier and no doubt will be officially taken
care of eventually. It is the duty of this society and school
authorities to urge proper legislation to cover lighting conditions
completely. It may be interesting to quote extracts from codes
already in existence.
Extracts from the Indiana "Sanitary School House Law" are
as follows :
Interior walls and the ceiling shall be painted or tinted some neutral
color, as grey, slate, buff or green.
All school rooms where pupils are seated for study shall be lighted
from one side only, and the glass area shall be not less than one-sixth of
the floor area, and the windows shall extend from not less than 4 feet
from the floor to at least 1 foot from the ceiling, all windows to be pro-
vided with roller or adjustable shades of neutral color, as blue, gray, slate,
buff, or green.
For left-handed pupils desks and seats may be placed so as to permit
the light to fall over the right shoulder.
Blackboards shall be preferably of slate, but of whatever material,
the color shall be dead black.
Abstract from the Rules and Regulations of the Indiana State
Board of Health are as follows :
No class-room shall exceed 24 feet in width, with the ceiling not less
than 12 feet nor more than 14 feet in height.
No window sash shall have more than four lights, and the tops of all
windows shall be square. When the proximity of other buildings or a
portion of the same building interferes with the proper lighting of a
class-room, the light shall be properly projected and diffused by the use
of prism glass.
When artificial lighting by means of electricity or gas is used the
lights shall be placed near the ceiling and the lights deflected by proper
shades toward the ceiling, either indirect or semi-indirect lighting being
used.
Where the light in any class-room is from the north, the proportion
of glass area to floor area should not be less than 1 to 5.
194 TRANSACTIONS I. E- S. — PART I
Architects, etc., shall certify hy affidavit indorsed on all plans and
specifications submitted that such plans and specifications comply with the
Indiana Sanitary Schoolhouse Law and with the rules of the Indiana State
Board of Health.
Abstracts from the Ohio State Building Code referring to
school buildings are as follows :
The height of all rooms, except toilet, play, and recreation rooms,
shall be not less than one half of the average width of the room, and in
no case less than 10 feet high.
The proportion of glass surface in each class, study "recitation high
school room, and laboratory shall be not less than i square foot of glass
to each 5 square feet of floor area.
Windows shall be placed at the rear or the left and rear of the pupils
when seated.
Tops of windows, except in libraries, museums, and art galleries, shall
not be placed more than 8 inches below the minimum ceiling height.
The unit of measurement for the width of properly lighted rooms,
when lighted from one side only, shall be the height of the window head
above the floor.
The width of all class and recitation rooms, when lighted from one
side only, shall never exceed two and one half times this unit, measured
at right angles to the source of light.
The candlepower of electric lamps shall not be less than the follow-
ing, viz. :
Auditorium 1 candlepower to 2Y2 sq. ft. of floor area
Gymnasium 1 candlepower to 2^ sq. ft. of floor area
Stairways and hall 1 candlepower to 4 sq. ft. of floor area
Class and recitation rooms 1 candlepower to 2 sq. ft. of floor area
Enclosed fireproof stairways, service stairways, corridors, passage-
ways, and toilet rooms shall be lighted by artificial light and said lights
shall be kept burning when the building is occupied after dark.
The Illuminating Engineering Society is taking up the matter
of the lighting of schools chiefly through a recently appointed
Committee on School Lighting. Observations have been made
and data have been collected for several years previous to the
appointment so that fairly definite activities were begun at once.
The following brief resume of requirements in school lighting
was presented to the Committee on Lighting Legislation for use
as a basis in formulating a code on school lighting. This is not
in complete form, but is expected to serve as a starting-point.
GENERAL CONSIDERATION.
The lighting of a school building should be referred to a com-
petent expert before the plans for the building are drawn. The
LUCKIESH : SAFEGUARDING THE EYESIGHT 195
importance of doing this early is evidenced by the fact that the
orientation of the building plays an important part in the design
of those features which depend for their satisfactoriness upon
proper lighting.
Minimum intensity of illumination, 2.5 to 3.0 foot-candles on
the plane of the desk top.
Polished surfaces such as blackboards, glossy paper, polished
desk tops, and glazed walls should be avoided.
Light sources (sky or artificial) should be well out of the ordi-
nary visual field.
Glare from blackboards should be avoided. This can be done
by carefully placing them, by lighting artificially, by tilting them,
and by keeping their surfaces mat. They should never be placed
between windows.
Excessive brightness contrasts should be avoided. A bright
source should not be viewed against a dark background. The
walls adjacent to a blackboard should not be too light in color.
Surroundings such as walls and ceilings should in general be
light in color. Ceilings and frieze should be practically white
(high reflecting power). Walls should be reasonably light.
Colors used should be white, grey, or tints of buff, cream or olive
green.
Children should be taught how to safeguard their vision; that
is, how to hold their books, to assume a correct position relative
to the light source, to complain of glare from blackboards, etc.
Teachers should be instructed to teach these fundamentals to
the children.
Good lighting should be incorporated in every course where
practicable and especially in the "home-making" course.
MORE SPECIFIC RECOMMENDATIONS.
Natural Lighting. — Window area should be ample — that is, an
appreciable percentage (say at least 20 per cent.) of the floor
area.
The windows should preferably be located on one side of the
room to the left of the students.
A portion of the sky should be visible from every desk top, at
least 5 degrees vertically.
5
196 TRANSACTIONS I. E. S. — PART I
The width of the room should not be more than twice the
window height.
The windows should be equipped with approved window shades
for controlling the light and excluding direct sunlight.
Prism glass should be used in extreme conditions at least.
Lighting and ventilating courts should be painted white.
Minimum illumination on desk top, 3 foot-candles.
Diversity of illumination not greater than 100 to I.
Artificial Lighting. — Ample general lighting is recommended.
Local units subject to control of pupils are condemned.
Minimum illumination on desk top, 2.5 foot-candles.
Light sources should be out of normal visual field if possible.
They should be equipped with diffusing glassware to reduce their
brightness and screen the source from the pupils' eyes.
Highest permissible brightness, 3 candlepower per square inch
when viewed against a light background.
Blackboards should be lighted by properly screened and judi-
ciously placed local units.
The system of lighting will depend upon many conditions. Any
well-designed system is satisfactory in its proper place. There
appears to be a growing tendency for the semi-indirect system.
It appears more generally satisfactory for class rooms, reading
rooms, etc. In the shops a direct system is advisable.
No local units should be used unless absolutely necessary.
CONDITIONS FOUND IN MODERN SCHOOLS.
There is a large amount of authoritative data available per-
taining to the best practise in natural and artificial lighting. Ref-
erences to many sources of valuable information are given in the
bibliography. The practises which the writer considers best are
already presented in a general manner throughout the paper.
Specific recommendations apply only to specific conditions, so it
is quite outside the scope of this paper to go into detail. It will
be enlightening, however, to consider some actual conditions —
good and bad — found in modern schools. It is gratifying to be
able to state that some of the cases of faulty lighting shown here
are being corrected. In general natural lighting conditions do
not appear as bad in the modern schools which the writer has
LUCKIESH : SAFEGUARDING THE EYESIGHT 197
had an opportunity to visit as the artificial lighting conditions
although there are opportunities for improving the former.
In Figs. 7 to 12 inclusive are found some very faulty artificial
lighting installations. The first general criticism is found in the
use of the local unit subject to the control of the pupil. The
average pupil knows practically nothing regarding the proper use
of light. In the drafting rooms pupils were found working in
the shadow of the hand or T-square when a slight adjustment
of the lamp in front of him would have given him satisfactory
lighting were it not for his neighbors' lamps which glared at him
from all sides. In Fig. 7 the units are fastened to the drawing
table. In this one respect this condition was more favorable
than the case shown in Fig. 8 where the units were practically
uncontrollable for they hung on drop-cords from a ceiling perhaps
12 feet in height with angle reflectors which could not protect
the eyes of the individual without causing a bad condition of
glare for many of his neighbors. The conditions were photo-
graphed as found on entering the rooms. Much more could be
said against such practise, but the photographs speak for them-
selves.
In Fig. 9 is found the condition in a machine shop in a tech-
nical high school. The complexity of shafting and belts make it
difficult to light this room by a system of general lighting. An
attempt has been made and yet it could be done more successfully.
If sufficient light cannot be directed to the lathes from overhead
units, local units could be used as a last resort. But these should
be shielded from all eyes by narrow concentrating reflectors
instead of being left bare as shown in Fig. 10.
In Fig. 11 is seen a condition not unusual in the shops of the
technical school. The photograph was taken in the position of
the eyes of a worker at one of the benches. Could one devise a
more discomforting condition of glare under which to work?
Equally bad conditions have been found in sewing rooms and
domestic science laboratories. A very faulty system used in a
sewing room is shown in Fig. 12. Glaring lights greeted the
worker from nearly every position in the room. The same criti-
cism applies here as in Fig. 8. An especially striking instance was
found in a "model" dining room where the young ladies were
I98 TRANSACTIONS I. E. S. PART I
being taught the principles of home-making. The furnishings
were satisfactory and were arranged in a manner which would
no doubt meet the approval of the seasoned house-wife, but above
the dining table was a fixture containing four bare carbon lamps
extending at an angle long ago condemned in lighting practise.
Brackets too low on the side wall contained bare carbon lamps.
The lighting system was wholly congruous but equally bad. This
was one of the most discouraging conditions encountered for it
showed that the director of the home-making course had no idea
that good lighting is one of the most essential features in making
a home attractive and comfortable. And further, these young
ladies were graduated without a knowledge of the possibilities of
lighting. The writer firmly believes that lighting has a socio-
logical importance of an unrealized magnitude. These are just
a few instances of bad lighting encountered in modern schools.
That rooms can be lighted well and inexpensively is shown in
Fig. 13. illustrating a foundry lighted by the direct method using
glass reflectors. The use of glass reflectors is commendable, for
the ceiling is not left in complete darkness as is the case with the
opaque reflector. Of course, this will be considered wasteful of
light by some, but a foundry is a dingy place at best, so the waste
is justified if it adds to the scanty cheerfulness.
In Fig. 14 is shown a large class room lighted inexpensively
by the direct method. This lighting is fairly satisfactory. It
would be excellent if the clear incandescent lamps were replaced
by bowl-frosted lamps. The latter should be used very generally
in lighting systems similar to that illustrated in Fig. 14. The
daylighting in this case is from two sides and the rear which is
not satisfactory.
In Fig. 15 is illustrated an approved method of direct lighting.
The lamps are hung high and screened by large, deep diffusing
reflectors. The natural lighting is likewise satisfactory.
In Fig. 16 is shown a large assembly room lighted with direct
units hung too low. This is a serious defect in this system. A
high hanging-height would convert this very unsatisfactory con-
dition into a fairly good example of so-called direct lighting.
Note the glare from the glazed desks and doors.
In Fig. 17 is shown a highly approved method of lighting for
t*
Figs. 7 and 8.— Examples of faulty drafting room lighting.
Figs. 9 and 10. — Examples of faulty shop lighting.
Fig. ii.— Faulty shop lighting.
Fig. 12.— Faulty lighting in a sewing room.
Fig. 13. — Satisfactory foundry lighting.
Fi£. 14— Satisfactory class room lighting.
Fig. 15. — An example of satisfactory direct lighting.
Fig. 16. — Unsatisfactory lighting in an assembly room. Units are hung too low.
Fig. 17. — An example of excellent semi-indiiect lighting.
Pig 1- An excellent example of indirect lighting.
EUCKIESH : SAFEGUARDING THE EYESIGHT 199
class-rooms — the so-called semi-indirect system. The light is
well diffused and the room has a cheerful appearance. The day-
lighting is from the left and the window area ample. Note the
glare from the desk top and image of the light source reflected
from the window. This latter illustrates that in a broad sense
proper lighting involves surroundings as well as the lighting
units. In Fig. 18 is shown an excellent example of indirect
lighting which is a very satisfactory system in the proper place.
Many auditoriums and class rooms are well lighted by this
method.
CO-OPERATION WITH SCHOOL AUTHORITIES.
The Illuminating Engineering Society through various com-
mittees and the individual efforts of members can be of consid-
erable assistance to school authorities in improving lighting con-
ditions, bringing about desirable legislation, and in promoting
the instruction of pupils in the correct use of the eyes and of light
sources.
The need for improvements in lighting has been shown from
several viewpoints. Certain conditions commonly found produce
glare from which discomfort arises and eye trouble may result.
Bad lighting promotes near-sightedness which in turn handicaps
the individual throughout life. Teach the pupil the fundamental
principles of conserving vision and a life-long benefit has been
bestowed upon him. But besides this, confront him with good
examples of proper lighting and the combination will be so far-
reaching in its effect that the benefit derived can not be estimated
in terms of the cost. It might also be well to note here that in
school lighting as in all other branches of illumination the ef-
ficiency of the system is the ratio of satisfactoriness to cost and
not the reciprocal of cost. The Illuminating Engineering Society
is prepared to co-operate with school authorities and it is to be
hoped that the latter will recognize that their position is a key-
stone to the promotion of the conservation of our most important
and educative sense-vision.
BIBLIOGRAPHY.
Ueber die neue Wengen'sche Methode das Tageslicht in Schulen zu prufeu.
Hermann Cohn, D. Med. Wochenschr., Berlin 28, 1902 (85-86,
102-104).
200 TRANSACTIONS I. E. S. — PART I
Ueber eine schuelle methods zur prufund der lichtstarke auf den arberls-
platzen in schulen.
E. Pfeiffer, Bureau und wekstatten Munchence med Worheuschr
49, 1902 (926).
Public School Room Lighting.
Knight and Marshall, Trans. I. E. S., vol. 5, 1910, p. 553.
School Lighting.
Ilium. Eng., London, Sept., 1910, p. 557.
The Conservation of Vision.
Dr. E. M. Alger, Trans. I. E. S., vol. 5, 1910, p. 1005.
School Lighting — Natural.
Dr. James Kerr, Ilium. Eng., London, Mar., 191 1, p. 154.
Artificial Lighting of Schools.
Dr. N. Bishop Harman, Ilium. Eng., London, Mar., 191 1, p. 157.
Notes on the Lighting of Some Schools and Colleges.
L. Gaster, Ilium. Eng., London, May, 191 1, p. 289.
An Analysis of Glare from Paper.
M. Luckiesh, Electrical Review and West. Elect., June 1, 1914.
Illumination of School Buildings.
V. R. Lansingh, Amer. School Board Jour., June, 1912.
Zeichensall, Bureau und Schul Beleuchtung.
Licht u. Lampe, Heft 115, 1912, p. 476.
Distribution of Natural and Artificial Light in Interiors.
M. Luckiesh, Trans. I. E. S., vol. 7, p. 388.
School Lighting and Eye Strain.
Ilium. Eng., London. Nov., 1912, p. 515.
School Lighting.
Ilium. Eng., Feb., 1913, p. 106.
Indirect Lighting at Rugby School.
Elec. Eng., July 10, 1913, p. 406.
Lighting of Schools and Libraries.
Jour, of Gas Ltg., July 15, 1913, p. 161.
Proceedings of Fourth International Congress on School Hygiene.
Buffalo, N. Y., 1913.
Lighting of Schools.
Jour, of Gas Ltg., Sept. 2, 1913, pp. 601, 616.
Organized Health Work in Schools.
Bulletin 44, 1913, U. S. Bureau of Education.
Lighting of School Rooms.
T. M. Young, Ilium. Eng., Oct., 1913, p. 498.
Value of School Room Lighting.
Elec. World, Oct. 4, 1913, p. 698.
Die beleuchtung von schulraumen und horsalen.
Licht u. Lampe, Oct. 9, 1913, p. 807.
LUCKIESH : SAFEGUARDING THE EYESIGHT 201
The Physiological and Mental Disadvantages of Unscientific School
Illumination.
L. Gaster, Ilium. Eng., London, Nov., 1913, P- 555-
Natural Lighting of Schools.
Ilium. Eng., Nov., 1913. P- 581.
School and Library Lighting.
Elec. Eng., Nov. 13, 19*3, P- 628.
Illumination School Lighting and Education.
Gas Light Journal, Nov. 24, 1913, P- 322.
School Lighting.
Electrician, Nov. 21, 1913, P- 275-
Uber lehrzimmerbeleuchtung mittels gas in den wiener stadtischen schulen.
F. Pohl, Jour. f. Gasbeleu., Jan. 3, 1914, P- *•
The Illumination of Burwash Hall, University of Toronto.
Elec. News, Jan. 15, 1914. P- 57-
Daylight Illumination in School Planning.
P. J. Waldram, Lond. Ilium. Eng., Jan., 1914.
School Room Lighting.
Romaine W. Myers, Jour, of Elec, Jan. 31, 1914, P- 96.
School Lighting.
E. H. Nash, Ilium. Eng., London, Feb., 19 14, P- 1^-
Some Experiments in School Lighting by Gas.
F. H. Gilpin, Light. Jour., Mar., 1914, P- 5°.
Illumination in the New Electrical Engineering Laboratory, Sheffield
Scientific School of Yale University.
C. E. Clewell, Light. Jour., Mar., 1914, P- 53-
School Illumination.
Gas Age, Mar. 16, 1914, P- 274.
Glare in School Illumination.
M. Luckiesh, Amer. School Board Jour., Apr., 1914.
Report on Daylight Illumination of Schools.
London Ilium. Eng., July, 1914.
Planning for Daylight and Sunlight in Buildings.
Marks and Woodwell, Trans. I. E. S., vol. 9, I9I4, P- 643.
Protection of the Eyes of School Children.
X. M. Black and F. A. Vaughn, Ophthalmic Record, Feb., 1913-
DISCUSSION.
Mr. S. G. Hibben: Even though semi-indirect lighting is
most excellent in schools, I do not consider direct lighting with
open bottom reflectors to be taboo. Under quite a number of
conditions, such as with units placed high enough to be well out
of the line of vision, direct lighting reflectors are satisfactory—
202 TRANSACTIONS 1. E. S. PART 1
in fact advisable whenever a good systematic maintenance or
cleaning system would probably be lacking.
A larger number of direct than of semi-indirect units is neces-
sary, both to secure a close approach to the same quality of
broadly distributed or multidirectional light, and also in order
to keep down the intrinsic brilliancies. The direct reflectors that
are recommended for the schools are deep, to shield the fila-
ments of the lamps, so that the proper sized shade for a ioo-watt
lamp in a classroom would be that which ordinarily would be
used with a 150-watt lamp elsewhere.
The chief factors influencing the performance of the semi-
indirect bowls are the density of the glass, and the hanging
height. It goes without saying that ceiling colors are vital. I have
found that of identically shaped bowls the medium density glass
will produce 25 to 30 per cent, more illumination on desk tops
than the heavy density opal. When a medium density bowl is
lowered from the ceiling, the illumination beneath it increases;
the reverse is often true when using a heavy density bowl.
I have considered it much better policy to use a larger sized
light-density glass bowl, rather than a small sized heavy-density
one. The common objection to the light-density glass is the rel-
atively high intrinsic brilliancy. This may be overcome by using
a larger bowl ; and even though the first cost be greater than
that of a smaller denser bowl, yet the increased efficiency or the
larger amount of light on the working plane, will eventually
more than over-balance the first cost.
Mr. G. W. Roosa : It might be a good plan to have rules on
optical hygiene printed on small sheets and pasted in every school
book. The necessity of safeguarding the eyesight and of better
school lighting cannot be too strongly enphasized.
TRANSACTIONS
OF THE
Illuminating Engineering Society
Vol. X APRIL 30,1915 NO. 3
ON THE CHOICE OF A GROUP OF OBSERVERS FOR
HETEROCHROMATIC MEASUREMENTS.*
BY HERBERT E. IVES AND EDWIN F. KINGSBURY.
Synopsis: In making measurements on colored light with the flicker
photometer the visual characteristics of the observers are of the utmost
importance. A group of readers should be chosen whose average is that
of an average eye. In this paper a method is described, by means of two
test colors, for selecting a group whose average characteristics shall be
those of the very large number who determined the photometric scale
used by the authors.
In the photometry of colored lights the selection of observers
is of exactly equal importance as the selection of an instrument
and of conditions of illumination and photometric field size.
Skill, previous experience and conscientiousness cannot make a
man normally color sensitive if he is born otherwise. Conse-
quently in selecting a group of observers who shall have in their
mean a normal eye, one may pass over the best "reader" in a
laboratory and use in his place the newest errand boy. In short,
where colored light photometry is in question, one must in the
choice of observers free one's mind as completely as possible
from any previous criterion and establish a new one based on
considerations of the nature of the observers' color vision.
In work recently presented before the Illuminating Engineer-
ing Society1 we have carried out extensive measurements of
differently colored lights, using throughout a definite photo-
metric method. This method comprises in part the use of a
* A paper read at a meeting of the Philadelphia Section of the Illuminating
Engineering Society, March 19, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
1 Experiments on Colored Absorbing Solutions for Use in Heterochromatic Photome-
try; Trans. I. E. S., No. 9, p. 795; 1914.
Additional Experiments on Colored Absorbing Solutions for Use in Heterochromatic
Photometry; Trans. I. E. S., 1915.
204
TRANSACTIONS I. E. S. — PART I
certain design of flicker photometer, under stated conditions, and
for the other part the use of a group of observers carefully
selected so that their results shall be the same as for a normal or
average eye. The instrument and method of use have already
been described. It is the purpose of this paper to describe both
the method of choosing the working group of observers and also
a means by which other laboratories can select a group of
similar characteristics.
The average eye now used in the laboratory of the United
Gas Improvement Company is based on measurements made by
sixty-one observers, this number being all that could conveniently
be obtained during a period of several weeks, and being as well
B
V
1
)
+c •<
S -1
I
J- ..
if
W
C -7
V
WAVC-LtHJTH
Fig. i.— Spectral transmissions of two colored solutions used in the selection
of a group of observers for heterochromatic measurements. A — 53 grams
copper sulphate to 1 liter of solution; B— 72 grams potassium dichromate
to 1 liter solution.
a large enough number so that the inclusion or exclusion of any
observer in the group would affect the result by less than half
of 1 per cent. The color measured was a monochromatic green
against the light of a carbon lamp. This was not chosen as a
criterion for general use, but was incidental to a determination
of the mechanical equivalent of light and further details will be
found in the account of that investigation.2
We shall first describe how our laboratory luminosity scale
has been maintained on the basis of these measurements, after
- The Mechanical Equivalent of Light; Physical Review, 1915.
Measurements on a Monochromatic Green Solution; Physical Review, 1915.
IVES AND KINGSBURY : HETEROCHROMATIC MEASUREMENTS 205
which we shall describe means by which this same scale can be
worked to in any laboratory.
The transmission of the special monochromatic green solution
as given by the mean of sixty-one observers is 0.0437. Indi-
vidual observers available in our laboratory vary from this as
much as 12 per cent, on either side. In selecting a group for
making a colored light measurement the procedure is simply to
pick a group of at least five whose mean reading on the test
color difference, as made and recorded once for all, is the true
mean. Thus the group of seven used in one of the measure-
ments on the blue solution previously described had obtained the
following values on the monochromatic green :
0.0474
0.0432
0.0416
0.0453
0.0398
0.0471
0.0418
Mean 0.0437
When any one observer of such a group was not available
either another was selected of very nearly the same character-
istics or, as was sometimes necessary, one or two other observers
of the group were replaced by a different selection whose mean
value from our record was again that of the sixty-one.
The luminosity scale maintained in this way has now been in
use in our laboratory for a period of many months. It has
proved eminently satisfactory. The different observers consis-
tently retain their characteristic positions. Measurements made
with different groups at various times have shown most excellent
agreement.
In order to make this method of selection of observers gen-
erally available, and insure at the same time that the same
luminosity scale is adhered to, we have thought it advisable to
adopt a different test color difference than that incidentally
obtained in the study of the mechanical equivalent of light. For
this purpose we have worked out two colored solutions of inor-
ganic salts which to the average eye, as determined by our meas-
urements, should have equal transmissions of the light of a
206 TRANSACTIONS I. E. S. — PART I
standard carbon lamp. At the same time an effort was made to
select transmissions each of which should give practically one
end of the spectrum alone. The idea of this was that if a group
of observers measures the ratio of the two halves of the spectrum
correctly it will probably measure any of the ordinary much less
pronounced color differences right.
The test colors which we now recommend are given by the
following aqueous solutions :
Yellow solution : potassium dichromate — 72 grams to 1 liter of solution.
Blue-green solution : copper sulphate — 53 grams to 1 liter of solution.
These, placed in two carefully matched tanks of 1 centimeter
thickness, should transmit equal amounts of the light of a stand-
ard "4-watt" carbon lamp, the measurement being made at
20 deg. C. by the flicker photometer under the conditions of
illumination and field size previously described. In regard to
the illumination, it is to be noted that the actual transmission of
these solutions is close to 70 per cent. In order, therefore, to
secure the equivalent of 25 meter-candles on a white surface the
lamp and distance should be arranged to give 35 or more meter-
candles, depending on the absorption of the optical parts of the
photometer. Needless to say, as in all precision photometry, the
test should be carried out by the substitution method, the two
solutions being alternated on the test side.
The transmissions of these solutions have been established by
a series of approximations involving a large number of measure-
ments all made in accordance with our original method of main-
taining the luminosity scale. This scale is now maintained by
using the new test colors in exactly the same way as outlined
for the monochromatic green and agrees, as it should, with the
original scale. That is, a group selected by their measurements
on these test colors as having a "mean eye" also possesses that
characteristic when tested by their measurements on the mono-
chromatic green solution.
A number of questions which arise in connection with the
choice of a group of observers in this way can be answered from
our experience. For instance, the question of what to do if
enough observers are not available to make a balanced group is,
we find, taken care of by giving double weight to one or two, in
such way that the same weighting gives equality with the test
IVES AND KINGSBURY: HETEROCIIROMATIC MEASUREMENTS 207
colors. Again the question arises as to the minimum number of
observers necessary. Is one observer, for instance, enough, if
he reads the test color difference correctly? We find in general
that it is hardly safe to depend upon one observer who tests
normal, because after all the test is to some extent arbitrary and
is not an absolute guide to an observer's performance on all types
of color differences. We have actually noted, however, that the
mean result of a certain pair of rather extreme observers (whose
vellow . , . N . .
values for —r-. are respectively 1.12 and 0.90) m a long series
blue
of measurements is almost uniformly the mean of the group, sug-
gesting that in many cases as few as two balanced observers
would be sufficient, but we would nevertheless recommend at
least five observers for precision work.
An important question which is frequently raised is that of
the permanence of an observer's characteristics. Will the mem-
bers of a group retain their relative positions over a period of
time? A large number of observations, extending over nearly a
year, have convinced us of the practical permanence of individual
color vision characteristics, with very rare exceptions. We shall
publish these data in another connection, but that portion obtained
in this present study may profitably be presented here. In the
series of measurements by which these two equal transmission
solutions were developed, the preliminary work was done with a
physical photometer (to be described shortly), after which two
series of visual measurements were made, at an interval of about
a month. In the first set seven observers participated and in the
second eleven. Of these, six measured in both sets. In the
following table we give the values of the ratios of transmission of
the two solutions (the actual ratio of each approximation being
taken as the unit) as obtained by these men at these two times:
Observer
I
2
3
4
5
6
Mean 0.992 °-997
Ratio — —
1st set.
2nd set.
0.957
o-973
O.946
O.965
1.002
I.052
0.910
O.904
1.042
1.068
I.043
I.074
208 TRANSACTIONS I. E. S. — PART I
It will be seen that with one exception the observers have
repeated to i per cent, or better. This one observer (number 3)
as it happens had, previous to this work, never read an optical
instrument and was used in the work chiefly because of his avail-
ability at all times. The one exception need not, therefore, be
given great weight. Even so, the mean value for this group of
six, on these extreme test colors, is only ]/2 per cent, different in
the two sets.
Another question is whether this method of selection could not
be used for observers to work with the equality of brightness
method. The answer is "yes>" provided it were possible to make
sufficiently definite and consistent settings by that method on the
test color difference to yield unambiguous results. Actually the
number of settings and the time which would be required defi-
nitely to determine an observer's characteristics by this photo-
metric method would be prohibitive. The method of selecting
observers is planned for the photometric procedure in which the
flicker photometer is used, and it is recommended for that only.
This paper, together with those which have preceded, to which
reference has been made, give full descriptions of instruments
and methods by which uniform results may be obtained in differ-
ent laboratories in the photometry of colored lights. A luminosity
scale has been developed — a matter of as much importance in
photometry as is a temperature scale in thermometry — to which
these uniform results are referred. The test colors just described
may be compared to the fixed points by which a thermometer is
calibrated.
haskell: lighthouse illumination 209
LIGHTHOUSE ILLUMINATION.*
BY RAYMOND HASKELL.
Synopsis: This paper describes the various forms of illuminants used
in the lighthouse service and discusses their application by means of lenses
and other means of intensification to lighthouses, buoys and light vessels.
In some form or other practically every system of illumination
and every type of primary light source, has at some time been in
use, or at least tried, for the purpose of lighthouse illumination.
Even totally indirect lighting has been seriously advocated in the
proposition to throw a strong beam upon the clouds. This, while
it theoretically gives height to the signal and hence greater range
of visability, would be impractical on account of the enormous
energy required and the uncertainty of clouds.
History informs us that lighthouses existed long before the
Christian Era, but, in comparison with modern installations they
were built more as curiosities or monuments, than as aids to
navigation. Later, however, a great many were constructed by
the Romans, and the sites of these are indeed in many cases
identical with those of modern lighthouses. The first lighthouse
structure built in the United States was situated in Boston har-
bor. This, however, was partly destroyed during the Revolution,
and the present Boston lighthouse, while on the same site, is a
fairly modern structure.
The oldest existing lighthouse towers in the United States are
situated on Sandy Hook and Cape Henlopen, but even in these
cases the lanterns and superstructures are comparatively modern.
ILLUMINANTS.
In ancient days, and in fact up to fairly modern times, the
illumination for lighthouse towers was produced by burning
piles of fagots or other material giving a comparatively large
flame. These were followed by the use of candles and various
types of primative seed oil lamps. Oils have been, and still are,
* A paper read at a meeting of the Philadelphia Section of the Illuminating Engi-
neering Society, November 20, 1914.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
210 TRANSACTIONS I. E. S. PART I
the principal sources of light used in lighthouses, the greatest
advance in their use being in the improvement of the lamps and
the manner of distribution of the light. Until recent times, veg-
etable or animal oils were the only ones used, the principal illum-
inant in the lighthouses of the United States being lard oil, but
since the discovery of petroleum, kerosene, in one form or an-
other, has formed the basis for light sources in the greater num-
ber of cases.
Both flat and round wicks are used, and for large installations
burners with as high as eight concentric wicks have been de-
veloped. There are still a considerable number of five wick
burners in use.
Since the advent of the mantle, wick lamps for the more power-
ful lights have been superseded in favor of the kerosene mantle
type of lamp. This form of light source, at the present time, is
the best, as to light efficiency and cost, known. Its only drawback
is the fallibility of the mantle and hence the necessity for having
a keeper to watch it occasionally and also to keep the lamps and
accessories in proper shape.
In large installations it is necessary to have a keeper anyway,
and therefore this system of illumination is almost universally
used in these cases.
The first incandescent oil-vapor (kerosene with mantle) lamps
used in this country were patterned after the French lamps, in
which the kerosene is vaporized by the excess and waste heat of
the mantle heating a tube containing the oil and situated over the
mantle. This, however, had its drawbacks in efficiency and reg-
ulation, and another type has been developed which allows free
passage of the light in all directions and gives a very high intrinsic
brilliancy. This high intrinsic brilliancy, as will be readily under-
stood, is the principal characteristic demanded by an illuminant
for lighthouse purposes. The cost of this lamp for fuel is about
i cent per 500 candlepower per hour, or including repairs and
depreciation, about 1.5 cents per 500 candlepower per hour.
Electricity, on account of the high intrinsic brilliancy as exem-
plified in the arc and concentrated filament lamps, presents itself
as the ideal source of lighthouse illumination. Its great drawback
however is its cost and the difficulty of obtaining it at most light
haskkll: lighthouse illumination 211
stations. Simplicity and reliability are the watch words in the
lighthouse service. Unless current can be obtained from power
companies on shore, the use of electricity is prohibited by the
cost of generating plants, the inability to make repairs on account
of isolation of stations, and the necessity of employing skilled
labor.
'Where current can be obtained, as in some shore stations, the
concentrated filament lamp is more or less ideal and is used sat-
isfactorily. Even here it must be watched, as lamps will burn
out and power lines will fail, but a lighthouse must stay lighted
regardless.
The electric arc is theoretically ideal as a concentrated light
source for use with lenses, but practically its drawbacks are many
and various. It has been found expedient, therefore, to utilize
this source only in a few instances, the most notable example
being Navesink on the Highlands, just south of Sandy Hook.
This is the most powerful signal in the United States, and cor-
respondingly gives an exceedingly quick flash.
Gas, either in the form of enriched oil gas or acetylene, is a
very important source of light in the lighthouse service, and is
used particularly in buoys or small beacons, where great intensity
is not demanded, and where it is impractical to have an attendant.
These gas installations will operate without attention from three
to six months, depending on the size of the burner and very little
trouble is experienced with them.
LENSES.
While the intensity of the source is important, the greatest
factor in lighthouse illumination is the means of intensifying or
directing the light energy in order to obtain the most usable re-
sult.
This was first accomplished by the use of metallic reflectors.
These are still used on some small light vessels, and when kept
highly polished are not a bad installation. In these cases eight of
these are so arranged on a carriage around the mast that they can
be lowered to the deck and attended to without exposing the men
to the weather.
The next development was the dioptric Fresnel, which was
212 TRANSACTIONS I. E. S. — PART I
followed by the complete lighthouse lens, containing both diop-
tric and catadioptric prisms. By catadioptric prisms is meant
those above and below the central belt which direct the light in
the desired direction, both by refraction and also by total reflec-
tion from the inner surface of the glass. This is shown by a
lens profile. In the central belts the light energy is directed hor-
izontally by refraction only. In the upper and lower prisms the
light is first refracted, then totally reflected and finally refracted
again. By means of these prisms the total energy from the source
at the centre is theoretically emitted in a parallel direction. In
cases of units which are known as fixed lenses, the prisms are
evolved around a vertical axis, and the resultant beam is a series
of parallel horizontal planes of light diverging in all directions,
in azimuth. With flashing and range lenses the prisms are
evolved around one or more horizontal axes, and the resultant
beams are theoretically cylinders of light. Practically on account
of the sizes of the sources the beams are solid cones of light
whose divergence depends on the dimensions of the source, and
whose intensity depends practically only on the intrinsic brilliancy
of the source, and on the solid angles subtended by the lens
panels at the focus. The flashing is produced by revolving the
lens around the source.
The mariner prefers a fixed light as it gives him something
steady to run by, but such lights are naturally lacking in intensity
and are often confused with shore lights. The flashing light is
very powerful but is of short light duration. With lenses of the
same focal length, the ratio of the period of luminosity to period
of darkness is indirectly proportional to the intensity of flash.
Where high power is not needed, but where it is desired to pro-
duce a distinctive light, it is customary to use a fixed lens, but
to cut off the light at definite periods by means of blanking
sections of the lens, and revolving it about the source of light.
This can be accomplished by extinguishing or blanking shutters
which periodically cover up or cut off the light from the source.
In order to utilize the light energy which is lost when a lens
panel is blanked off, it has been found expedient to install silvered
spherical mirrors in place of these blanking panels. By prop-
erly arranging the mirrors the light, which would strike a blank
HASKELL: LIGHTHOUSE ILLUMINATION 213
panel, can be reflected back through the source and out through
the lens on the opposite side, thereby intensifying that beam very
greatly. With sources of illumination that are transparent, as
acetylene gas, this method is very efficacious, but with sources
which are quite opaque, as mantle lights, the gain from this
scheme is scarcely 25 per cent. To obviate this loss the idea
was conceived that instead of sending the energy back through
the focus, it could be sent back alongside of the focus just missing
the mantle. Theoretically this would not produce good results,
as the lenses are designed for a point source at the focus, but
practically the sources are generally so large that the fact that
the image is not at the focus is scarcely realized, and from 80 to
85 per cent, of the otherwise lost energy can be utilized in use-
ful light. With fixed lenses this intensifies the beam. When used
with flashing lenses it increases the relative light period.
In using this principle of offset mirrors it has been found most
practical to split the mirrors vertically, and so set them as to
send the reflected light on both sides of the mantle instead of
all on one side.
As mentioned above the usual method of producing occulting
or flashing lights when gas or electricity is not used for the illum-
inant is by means of revolving the lens. This is done by clock-
work actuated by weights. The lenses are often very heavy and
are generally supported on chariots, ball bearings or floated in
mercury. For the heavy lenses the mercury float method
is found to be the best. By the proper design of mercury float,
a two-ton lens can be carried on less than 50 pounds of mercury
and the whole thing can be revolved by a few ounces constant
force. This requires, however, that the parts of mercury float
outfit shall be machined and set up exceedingly true, and also
that the lens shall be very well balanced. In order to use oil-
vapor lights, it is necessary on account of the tanks containing
oil and air under pressure, that the lamp shall be stationary and
the lens revolve around it.
The most powerful flashing lens ordinarily used is what is
called the bivalve. This consists of two hemispherical shaped
panels, the prisms of which are so arranged as to concentrate
practically all the light emitted by the source into two diametri-
214 TRANSACTIONS I. E. S. — PART I
cally opposite beams. The flash emitted by these bivalve lenses is
very powerful, but is of short duration, in many cases of less than
one tenth second duration. When it is desired to utilize the
beam in only one direction, as in the case of a range lens show-
ing light only in one direction along a channel, one half of a bi-
valve can be used and intensified by the substitution of mirrors
for the other half. This condenses and directs all the light
emitted by the source in one direction in a search light beam.
By proper design of prisms and panels it is possible to flash
numbers, as in the case of Minots Ledge, which flashes 1-4-3, or
as in other cases to make combinations of red and white flashes.
These special combinations are used in cases where a number of
lights together are likely to produce confusion.
The manufacture of lenses is quite a delicate operation, and
until lately such work has been done abroad. This has been due
partly to the fact that the largest factor in the cost is labor, which
can be obtained much cheaper abroad than here, and also to the
fact that the demand has not been sufficient to warrant the initial
outlay necessary.
Recently, however, American manufacturers have gone into
this industry and by the use of machinery are making better
lenses than those obtained abroad, and it is believed it soon will
be a paying proposition to them. The advantage of the American
made lens over the foreign one lies in the use of machinery in-
stead of hand labor, whereby all similar prisms are exactly alike
and interchangeable, and repairs can be easily made. In foreign
lenses the prisms rarely are the same and repairs are very ex-
pensive.
LIGHT INTENSITY.
A great many attempts have been made to compute the candle-
power values produced by various lenses, but there are so many
factors entering into this computation that a formula becomes too
loaded down to be workable. They all end up by making some
assumption or other which is never practical and vitiates the
whole computation. In working out candlepower values the
Unit d States Lighthouse Bureau has used the empirical method,
obtaining all the data it could and then using simple formula for
rpolation. The values were obtained by actually measuring
HASKELL: LIGHTHOUSE ILLUMINATION 215
such lenses as were available with the different sources of lights
used in the service.
The following results are worth noting. With small lenses the
candlepower increases up to 150 feet and then remains constant
no matter how far away it is taken. With large lenses the
maximum is reached at 250 to 300 ft. (75 to 90 m.), and
further increase of distance causes no change. This is largely
due to the fact that the sources of light are fairly large. As a
general rule the maximum is reached soon after a point is
reached where all the prisms fill with light.
Fixed lenses with the same light source are found to vary
in candlepower directly with the diameter; flashing lenses of
similar construction vary approximately as the square of the
diameter decreasing and departing, however, from this law
somewhat as the larger lenses are considered. This is probably
due to the fact that the prisms in the larger lenses are thicker and
not so well set as the medium sized ones. With fixed lenses the
candlepower varies directly as the intrinsic brilliancy and as the
width of the light source, but does not depend on its height. With
flashing lenses the candlepower depends only on the intrinsic
brilliancy, the large sources producing only more divergence of
beam and no increase of candlepower.
The dioptric portion of the lens, approximately 300 above and
below the central plane, produces about 60 per cent, of the light,
the upper catadioptric portion 30 per cent, and the lower 10 per
cent.
All of the above facts would be naturally foretold by geomet-
rical optics, but it is always pleasing to have theory so well cor-
roborated.
The brightest light in the United States is on the Highlands
of the Navesink where an electric arc is intensified by a second
order bivalve lens. It is estimated at 25,000,000 candlepower.
BUOYS.
The lighted buoy is more or less a modern invention. At one
time an attempt was made to have a string of buoys in one of
the channels of New York harbor lighted by electricity and sup-
plied by a cable from the shore. They gave so much trouble,
2l6 TRANSACTIONS I. E. S. — PART I
however, that they were abandoned. The next development was
the use of oil or Pintsch gas, each buoy being a unit by itself.
The gas is contained in the body of the buoy under up to 180
pounds (12 atmospheres) pressure and burns in a protected lan-
tern at the top. In order to save gas and give character to the
light, a mechanism is installed in the lantern which automatically
and periodically turns the gas on and oft*. A small flame or pilot
burns continuously in order to light the gas when it is automati-
cally turned on. The mechanism is simple and operated by the
gas pressure, and barring accidents will operate as long as there
is gas in the buoy. Ordinarily these buoys will run without at-
tention from four to nine months, depending on the flashing
period of the light.
These buoys are very easily filled at their stations by simply
lashing the buoys to the side of a lighthouse tender, attaching a
hose and pumping the gas into them from a large storage holder
carried on deck. The crews of these vessels become quite expert
in securing these buoys for attention even in rough seas, and it
is surprising how little damage is done to them.
The candlepower of an ordinary oil gas lantern, however, is
low and in hazy weather especially it cannot be seen at any
great distance. To increase its light intensity, in many cases
the gas is burned with a mantle. The use of the mantle intro-
duces, however, a more or less uncertain factor. Sometimes a
mantle will operate for many months satisfactorily without
failure, while another mantle from the same manufactured lot
will fail very quickly. These lights therefore are generally used
in places where they can be observed every few days and given
attention if necessary.
The most modern gas illuminant is acetylene. This is burned
in a lantern more or less in the same manner as oil gas, only the
mantle is not used. This gas, however, cannot be compressed
with safety into the body of the buoy, and so is stored in tanks,
dissolved in acetone. These tanks fit into pockets in the buoy
and are so arranged that they can be easily removed and replaced
on station by a boat alongside.
Another form of buoy more or less in use generates the acety-
lene at low pressure directly from calcium carbide stored in the
HASKELL: LIGHTHOUSE ILLUMINATION 2\J
buoy. Theoretically this should be the most economical method
to produce acetylene, but practically it is unsatisfactory. Owing
to high seas and waves the buoys often do not generate evenly
and considerable gas is lost. It is impossible to tell exactly how
long a buoy is going to run which makes it administration costly
on account of tender costs. There is a buoy of this type in New
York harbor which ran sixteen months on a single charge, and
then the next time it went out in two months.
In order to save gas in the day time it is possible to equip gas
apparatus with a mechanism which is operated by the light of the
sun and turns the gas off in the day time. These so called "sun
valves" operate quite satisfactorily, especially on large installa-
tions where considerable gas is consumed, but with small lanterns
the depreciation and repairs of the sun valve is greater than the
cost of gas saved. This is especially true of buoys where the
danger of being damaged by passing vessels is great.
LIGHT VESSELS.
Perhaps the most important aid to navigation is the light
vessel. These are vessels anchored at well known sailing points
whereby the mariner can get a perfect idea of his position in
thick weather without the danger usually attendant in running
too near a lighthouse. Light vessels being anchored in reason-
ably deep water, the mariner runs close to them and can get an
accurate point of departure for shaping his course, while light-
houses being on land the mariner cannot run near to them and
especially in thick weather must more or less guess at his posi-
tion. In addition to signal lights these vessels all carry an air
fog signal and most of them submarine bells.
The characteristic lights of a light vessel are carried at or near
the mast head and consist practically of the same systems as
enumerated above. The small vessels are equipped with oil
lamps with reflectors or with small lenses and lanterns. These
are arranged on frame work around the mast so designed that it
can be lowered to the deck and given proper attention without
the necessity of the men going aloft in bad weather.
A large number of vessels are being equipped with gas ap-
paratus, particularly acetylene on account of its simplicity and
2l8 TRANSACTIONS I. E. S. — PART I
ease of handling. This gas apparatus has the further advantage
that the lanterns can be fixed permanently at the mast head and
thus gain several feet in height over the oil light installations.
Most of the larger vessels are equipped with electric plants and
the sources of illumination are concentrated filament 250-watt
tungsten lamps in 300 mm. lanterns. These give a most satis-
factory light and require little attention, the only drawback being
the necessity for a complete electric plant. One vessel,
"Ambrose" at the entrance to New York harbor is equipped with
flaming arcs in 300 mm. lanterns. These of course give a very
powerful illumination, but it is really greater than is necessary
to correspond with the elevation of the lanterns. These lights
are so bright that there is complaint that they prevent the pilots
from detecting other ships approaching from back of the light
vessel.
Both light vessels and lighthouses will soon be displaced in a
large number of cases with big buoys. These are being made
now with very heavy bells and strong whistles, and on account
of the lower initial cost and maintenance, several can be used
instead of one light vessel, for the same cost and a much broader
system of guide posts of the sea can be established. The mariner
will simply run between buoys, a few miles apart.
sharp: data on artificial daylight units 219
SOME DATA ON ARTIFICIAL DAYLIGHT UNITS.*
BY CLAYTON H. SHARP.
By projecting a spectrum on to a card covered with skeins of
worsted of all the principal spectral colors, including also purple,
it was shown how the colors of fabrics vary as seen in different
colored lights. Thus a red worsted is black in green and blue
light and a blue one is black in the red light. Therefore it is
necessary in order that colored fabrics may always be seen alike
that they always be viewed under light of the same spectral com-
position, having that is, the same relative intensities of each of
the colors. As a standard of composition of this sort, daylight
is chosen and this is called "white light."
The colors of fabrics are obtained in one of two ways; either
by the use of a pure dye or by mixing two different dyes together.
For instance, a green may result from the use of a pure green
pigment or it may result from the admixture of blue and yellow.
Two greens differently made up might match in one light,
whereas with light of a different spectral composition, they would
be differently affected and hence would not match. The use of
the daylight equipments is to provide this standard white light
of a given spectral composition for the purpose of matching
colors. In certain respects an equipment of this kind is better
than daylight, inasmuch as it is always of a fixed value and does
not vary continually as daylight does, both in color and intensity.
The following daylight equipments were exhibited and data
obtained at the Electrical Testing Laboratories and made avail-
able through the courtesy of the Lamp Committee of the Asso-
ciation of Edison Illuminating Companies were given.
The principle of the operation of these equipments is that by
the interposition of a bluish screen between the light source and
the object to be viewed, the excess of red and yellow in the light
source is removed, and the spectral composition of the resultant
light becomes the same as that of daylight.
* Summary of a lecture delivered before a meeting of the Xew York Section of the
Illuminating Engineering Society, November 14, 1914.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
220
TRANSACTIONS I. E. S. — PART I
Description of
equipment
Character of
the light source
A Moore carbon dioxid tube
B Special Welsbach mantle
C Intensified arc
D Gas-filled tungsten lamp
E Gas-filled tungsten lamp
F Gas-filled tungsten lamp
Character of
the screen
None.
Greenish-blue pebbled glass
and purple gelatin.
Composite of small pieces of
blue, green and clear glass
with diffusing glass.
Bluish glass.
Globe of bluish glass, sand-
blasted on the interior.
Globe of blue glass flashed
with opal.
Data on Illumination Produced.
Equipment B.
The illumination values found are shown on the accompanying
chart. The center of the field was much brighter than the
edges.
Equipment C.
The following values were obtained :
Horizontal foot-candles
Location of test station
Directly beneath center of screen...
1 ft. out from center of screen
2 ft. out from center of screen
3 ft. out from center of screen
4 ft. out from center of screen
Equipment D.
The following values were obtained :
Horizontal foot-candles
i ft. iS in.
Location of test station below screen below screen
Directly beneath center of screen 52 18.0
3 in. out from center of screen 36 —
6 in. out from center of screen 11 8.5
1 ft. out from center of screen 4 3.0
18 in. out from center of screen — 1.5
Note: Illumination very non-uniform. Bright spot directly
beneath unit.
18 iii.
below screen
3 ft.
below screen
50.0
13-4
26.O
13-2
5-6
8.4
1.4
2.5
—
1.0
A (on left)— Moore carbon dioxid tube; B (on right)— A special gas mantle daylight producer.
C — Intensified carbon arc lamp with
color screen.
F — Tungsten lamp in a blue glass globe
flashed with opal.
1000
410 450 490 550 570 6)0 650 690
VIOLET BLUE GREEN YELLOW 0RAM6E RED
WAVE-LENGTH
Fig. I.— Spectrophotometric curves of the daylight equipments.
sharp: data on artificial daylight UNITS 221
Absorption Data.
Equipment C.
Arc lamp unequipped, mean spherical cp 151
Arc lamp with reflector, mean spherical cp 107
Arc lamp with reflector and color screen 11
Absorption due to screen 90 per cent.
Equipment D.
Lamp equipped with reflector, mean spherical cp. 57.8
Lamp equipped with reflector and color screen... 3.56
Absorption due to screen 94 percent.
Equipment E.
Absorption 64 per cent.
Equipment F.
Absorption 73.5 per cent.
The spectrophotometric curves of these equipments are given
in the accompanying figure. Daylight curve ascribed to Ives
refers to the blue sky.
The Moore carbon dioxid tube has been suggested as a stand-
ard of white light and may in this case be used as a proper
standard for comparison.
222 TRANSACTIONS I. E. S. — PART I
BOOKS ON ILLUMINATION.
The table* on the following pages gives a classified analysis of all the
available books, in English, pertaining to illuminating engineering. It
indicates the possible utility of these books for illuminating engineer-
ing practise. The distributions under the various subject-headings con-
stitute, of course, an index rather than a precise analysis of the
contents of the books. Moreover, the classification, as might be
expected, is necessarily more or less arbitrary. For example, " Private
House Electric Lighting" by Taylor describes small plants for generation
of electricity, and the practical wiring and placing of lamps in residences.
It has been classed under the heading " G," but there are also good reasons
for classing it under " D," " M," " Q," or " U."
Catalog of Various Subjects Covered by Table I.
A. Physical basis of light production.
B. Physical characteristics of sources.
C. Chemistry of light production.
D. Electric illuminants.
E. Gas and oil illuminants.
F. Incandescent gas mantle lamps.
G. Electric and gas lighting (gen. mfgr. and dist.)
H. Units, standards and terminology.
I. Photometry.
J. Architecture.
K. Physiology and psychology.
L. Calculations.
M. Interior illumination.
N. Exterior illumination.
O. Reflectors, glassware, etc.
P. Fixtures.
Q. Commercial aspects of electric and gas lighting.
R. The Illuminating Engineering Society.
S. Illuminating engineering.
T. Color.
U. Miscellaneous.
* This table, which was prepared by Mr. Norman Macdonald, has been abstracted
from the annual report of the 1913-1914 Committee on Education of the Illuminating
Engineering Society.
BOOKS ON ILLUMINATION
223
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gove and porter: car lighting problems 227
A PRACTICAL STUDY OF CAR LIGHTING PROBLEMS.*
BY W. G. GOVE AND L. C. PORTER.
Synopsis: This paper describes very exhaustive tests conducted by
the New York Municipal Railway Corporation in order to determine the
best method of lighting the 600 new cars under construction for the new
subway in New York City. Direct, semi-indirect and totally indirect
lighting systems were tried in a full sized template car, built for the
purpose. Both standard equipment and equipment especially constructed
for the purposes were tested, the construction of the car being changed
where necessary. As a result of the tests, the system finally adopted
consisted of a single row of 56-watt tungsten railway lamps located down
the center line of the ceiling and equipped with intensive type opal glass
reflectors, this system offering the best combination of desirable factors,
including good lighting, reasonable installation cost and low maintenance
cost.
When the plans for the new subway in New York City were
being completed, it was decided that the six hundred cars should
be the latest word in car construction in every detail. Many new
and interesting mechanical and electrical devices, which have
been described in the various technical bulletins,1 were decided
upon for these cars. Not the least of these most up-to-date
factors was the lighting of the cars. The size, interior seat ar-
rangement, finish and construction of the cars presented many
new problems to be solved in choosing a lighting system which
would meet satisfactorily the following desiderata :
( 1 ) Quantity of light ; it being desirable to have an average
intensity of not less than 3 foot-candles on a hor-
izontal plane 42 in. (1.06 m.) above the floor, at
85 per cent, normal voltage.
(2) General effect and appearance of lighting system with
lamps lighted or extinguished.
* A paper read at a meeting of the New York Section of the Illuminating Engi-
neering Society, March II, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
1 Electric Traction, A. E. R. A., Dec, 1914.
JJS
TRANSACTIONS I. E. S. — PART I
(3) Lack of eyestrain for both seated and standing
passengers, involving not only intensity and
direction of light, but also glare and possible
shadows cast by standing passengers on the read-
ing matter of seated passengers.
(4) Efficiency.
(5) Installation and maintenance expense.
(6) Depreciation of equipment in service.
In order to make a thorough study of these problems a series
of tests were conducted in a full-sized model car constructed for
the purpose. This car was 67 ft. 3 in. (20.42 m.) overall, by
9 ft. 10 in. (3 m.) wide, by 12 ft. 3 in. (3.73 m.) high. The in-
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Fig- I. — I'lan and elevation of New York Municipal Railway Corporation's
subway tempate car.
terior dimensions of the body used in the tests were 65 ft.
(19.81 m.) long by 9 ft. (2.74 m.) wide. Fig. 5 is an exterior
view of the car. The interior car finish was white enameled
headlining and walls, down to the window sills. Below the sills
the walls were painted grey. The floor was concrete and the
seats upholstered in yellow rattan. Fig. 1 shows the interior
seating arrangement and gives the general dimensions of the
car.
Photometer tests were taken to supplement such data as ob-
servation of the general appearance, installation and maintenance
cost figures, etc. The photometric measurements were not made
with the intention of comparing the efficiency of any particular
types of illuminating devices or accessories thereto; though the
GOVE AND PORTER: CAR LIGHTING PROBLEMS 229
average intensities obtained were used in securing the relative
utilization efficiencies of the various lighting sy6tems tested.
In making the photometer tests stations were chosen 2 ft.
apart in a horizontal plane 42 in. (1.06 m.) above the car floor,
over one quarter of the floor area. The entire car, however, was
equipped with lighting units. Five readings were taken at each
station, on a portable photometer, recalibrated before each test.
In order to make one reading comparable with any other, sim-
ultaneous voltage readings were taken, as it was found to be
impracticable to hold constant voltage on the lamps. Each
photometer reading was corrected to normal voltage from the
characteristic curves of the lamp and the five corrected readings
averaged to obtain the station value. In obtaining the average
intensity for the entire car, weight was given the stations in
proportion to the area covered. The illumination values were
also calculated for 85 per cent, normal voltage, in order to see
what illumination would maintain under that condition.
The same lamps, as far as practicable, were used in the various
reflector equipments. As the tests were made to find out approxi-
mately what would be the average operating condition in new
cars, and not to determine the exact efficiencies of the different
reflectors, figures were based on the manufacturers' data book
ratings of the lamps.
It was decided before the tests started that tungsten filament
lamps would be used for illuminants, the question being as to the
best method of applying the lamps. Three systems of illumina-
tion were tried out, i. e., (a) direct lighting, (b) semi-indirect
lighting, (c) totally indirect lighting. In working up various
applications of these three systems, a study was made of existing
installations, supplemented by many suggestions for improve-
ment from various lighting experts and practical railway men.
In order to carry on the tests the interior construction of the car
was altered when necessary.
Photographs of the interior of the car were taken with the
lamps burning. The exposures were timed to exactly two min-
utes. These photographs were intended for comparative pur-
poses only. They have no bearing on the photometric readings,
230 TRANSACTIONS I. E. S. — PART I
except to indicate (in a comparative way) the high and low
lighting throughout the car.
The direct lighting tests made were as follows:
DIRECT LIGHTING TESTS.
No. 1. — The lighting units used in this test consisted of a
single row of 14 6-in. opal glass reflectors (see Fig. 6) mounted
along the center line of the ceiling and spaced as shown in Fig.
2. Ten of these reflectors were equipped with 56-watt clear bulb
tungsten railway lamps (wired in two circuits of five lamps each
in series) and the remaining four with 10- watt clear bulb tung-
sten emergency lamps.
The variation from even spacing shown on Fig. 2 was neces-
sary on account of the construction of the model car, but would
be corrected in the cars as finally built. The light distribution
(Fig. 2) was good, though it had points of high intensity under
the emergency lamps, due to the small lamp in large reflector.
No bare lamp filaments were visible along the normal line of
vision. The efficiency of the system was high, installation costs —
on account of the single row of large units — were low, and main-
tenance was good, the smooth surface of the reflectors facilitating
rapid cleaning. The general appearance of the lighting system in
the car was pleasing (see Fig. 7) and the illumination good,
averaging 5.7 foot-candles at normal and 3.2 at 85 per cent,
voltage, with an energy consumption of 1.03 watts per square
foot. There were 5.54 effective lumens per watt and the effective
utilization efficiency was 68.7 per cent. It is interesting to note
that the utilization efficiency in an ordinary dark yellow trolley
with similar equipment is about 30 per cent., showing the great
advantage (from an efficiency-of-light-utilization standpoint) of
the white enamel interior finish.
No. 2. — The second direct lighting test was similar to the first,
except that clear prismatic reflectors were used. The change
of reflectors raised the average foot-candle intensity to 6.1 at
normal and 3.4 at 85 per cent, voltage. The effective lumens per
watt were increased to 5.90 and the utilization efficiency to 73.2
per cent. The maintenance of this equipment would be slightly
GOVE AND PORTER: CAR LIGHTING PROBLEMS
231
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higher than with the glass used in the aforementioned test, due
to cleaning the prismatic glass. There was also a little more
glare, though not an objectionable amount. The choice between
these two reflectors, therefore, is largely one of esthetic taste.
No. 3. — In the third direct lighting test 5 94-watt clear tungsten
filament railway lamps, equipped with clear prismatic reflectors
were located in a single row down the center line of the ceiling.
Four 10-watt tungsten emergency lamps in clear prismatic reflec-
tors were located between these. The resultant average intensity
in the car body was good, but due to the relatively low hanging
height and wide spacing of the units the distribution was very
uneven (see Fig. 4). The installation and maintenance of the
system would be low, on account of the small number of large
units to install and clean. The average foot-candles obtained
were 5.0 at normal and 2.8 at 85 per cent, voltage. The energy
consumption was 0.87 watt per square foot ; effective lumens per
watt 5.75; and effective utilization efficiency 71.5 per cent.
Xo direct lighting tests were made with lighting units located
on the half decks. Previous experience and tests had shown
that center-deck direct lighting may produce perfectly satisfac-
tory illumination, free from sharp shadows and glare. It was
felt that the possible gain of a few per cent, in efficiency with the
half-deck lighting did not warrant the additional installation and
maintenance expense (due to a larger number of smaller units to
install and clean) accompanying this system of lighting.
SEMI-IXDIRECT LIGHTING TESTS.
No. 1. — A very interesting method of lighting was used in the
first test. Twelve special 80-watt 95-volt turnip-shaped tungsten
lamps, opal dipped over the tip half, were installed down the
center line of the ceiling. Each lamp was suspended by an
inverted white enameled cone, shown in Fig. 8. Three 10-watt
tungsten emergency lamps were also used in small rosettes. The
80-watt lamps were connected six in series. All of the filament of
the 80-watt lamps was located below the center of the bulb;
hence, none of it was in the line of vision. The opal on the
lower half of the bulb served a double purpose, i. e., to protect
Fig. 5.— Outside view of New York Municipal Corporation's subway car.
Fig. 6.— Showing installation of 56-watt railway tungsten filament lamps in
white glass reflectors.
Fig ;.— Lighting effect of installation shown in Fig. 6.
Fig. 8.— Installation of 12 special 80- watt, 95-volt, turnip-shaped, opal-dipped bulb, tungsten
filament lamps, suspended without reflectors from white euameled cone shaped
fixtures.
Fig. 9.— Installation of 56-watt tungsten filament railway lamps in special convex reflector.
Fig. 10.— Semi-indirect lighting; each bowl contains two 94-watt tungsten filament
railway lamps and one 10-watt tungsten emergency lamp.
Fig. ii. — fighting effect from a semi-indirect installation with special ceiling insert.
Fig. 12.— Showing installation of tungsten filament lamps and special curved
white glass screens.
GOVE AND PORTER: CAR LIGHTING PROBLEMS 233
the passengers' eyes from the glare of the bare filament and also
to reflect the light up to the ceiling. The particular advantage of
this system of lighting was that it eliminated the necessity of
reflectors, special holders and other accessory equipment; thus
lowering both installation and maintenance costs. The illumina-
tion was fairly uniform (Fig. 3), though the uneven spacing
necessitated by the car construction made it unnecessarily high at
the center. As the entrance and exit doors were located here,
however, this was no great objection. The average intensity was
J.J foot-candles at normal and 5.1 at 85 per cent, voltage. The
energy consumption was 1.69 watts per square foot, the effective
lumens per watt 4.65, and the utilization efficiency 58.4 per cent.
The appearance of the car lighted was pleasing. The lamps,
being located on the center line of the car, did not interfere with
the clear reading of advertising signs located along the sides.
Xo. 2. — In the second semi-indirect lighting test a novel equip-
ment was used (Fig. 9). Ten 56-watt clear tungsten railway
lamps were located on the center line of the ceiling, supplemented
by 4 10-watt tungsten emergency lamps. Six inches (15.2 cm.)
below the ceiling and extending the entire length of the car, was
suspended a reflector consisting of a white enameled board 11 in.
(28 cm.) wide, convex on a 16- in. (0.4 m.) radius. The bowls
of the 56-watt lamps extended through holes cut in this reflector.
Under each hole was fastened a white glass dish to diffuse the
glare of the bare lamp filament. The spacing of the lamps is
shown in Fig. 13. The plan in using this combination was to
utilize as much as possible of the direct light from the lamp, to
illuminate the advertising signs ; the indirect light to give even
distribution and the direct light to brighten up the under side
of the reflectors. Distribution curves from this equipment are
shown in Fig. 13. The light distribution was good, but the
intensity low, averaging 3.9 foot-candles at normal and 2.2 at
85 per cent, voltage. The watts per square foot were 1.03; effec-
tive lumens per watt 3.81 ; and the effective utilization efficiency
was 47.2 per cent. The resultant illumination was pleasant, but
the appearance of the lighting equipment was rather crude, sug-
gesting a watering trough down the center of the car. It was a
curious fact that while both sides of the reflector and the ceiling
234 TRANSACTIONS I. E. S. — PART I
were painted alike, the under side of the reflector appeared grey.
due to the lower intensity of light on it.
Another test was conducted on this same equipment with the
interior finish of the car silver grey instead of white. This
change lowered the effective utilization efficiency about 10 per
cent.
The next semi-indirect equipment tested consisted of 10 94- watt
tungsten railway lamps equipped with 5 13-in. (33 cm.) white
glass bowls, mounted down the center line of the ceiling. There
were 2 94- watt lamps and 1 10- watt emergency lamp in each bowl.
(See Fig. 10). The bowls were hinged, allowing of lowering
for cleaning and lamp replacement. The bowls were suspended
with their tops located 12 in. below the center of the ceiling.
The illumination from this system was very uneven, being high
directly under the units and low between them (see Fig. 14).
The average intensity was 5.7 and 3.2 foot-candles at normal and
85 per cent, voltage, respectively; watts per square foot 1.69;
effective lumens per watt 3.36; and effective utilization efficiency
41.5 per cent.
In order to determine the effect of the shape of the ceiling on
the light distribution, a special headlining consisting of a white
enameled insert, having a 3 ft. (0.91 m.) span on an 18 in.
(0.45 m.) radius, was inserted and the test repeated. Fig. 11
shows the appearance of the insert and illumination effect. This
resulted in raising the average foot-candles to 6.1 and 3.4 at
normal and 85 per cent, voltage, respectively ; effective lumens per
watt to 3.62 ; and the utilization efficiency to 44.7 per cent. The
distribution curves of this equipment are shown in Fig. 15.
The insert was then removed and the test repeated with a dif-
ferent spacing of the units. This resulted in a little improve-
ment in distribution. The principal trouble with this installation
was that the headroom in the car was not sufficient to allow the
lighting units to be hung the proper distance below the ceiling.
The next equipment tested required special reflecting devices.
Ten 56-watt clear tungsten railway lamps were located in a single
line down the center of the ceiling, with 5 10- watt all-frosted emer-
gency lamps in rosettes between them. Each 56-watt lamp was
equipped with a screen made from a circular piece of glass bent
i
GOVE AND PORTER: CAR LIGHTING PROBLEMS 235
over a cylinder (Fig. 12). This resulted in a screen 11 in.
(27.9 cm.) long by 8 in. (20.3 cm.) wide by 3 in. (7.62 cm.)
deep. When these screens were hung beneath the lamps with
their open ends towards the sides of the car, it was impossible
to see the lamp filaments from any part of the passenger car
body; at the same time the direct light from a considerable
portion of the lamp fell on the ceiling and reached the reading
plane with but one reflection, making the system fairly efficient.
The distribution lengthwise of the car was even, though the out-
board seats received considerably less light than the center aisle
of the car (Fig. 20). The average intensity was 4.8 and 2.7 foot-
candles at normal and 85 per cent, voltage; the energy consump-
tion 1.04 watts per square foot; effective lumens per watt 4.63;
and effective utilization efficiency 57.6 per cent. The chief ad-
vantage of this equipment was the ease with which the reflectors
could be cleaned. The appearance of the car lighted was rather
pleasing.
TOTALLY INDIRECT TESTS.
No. 1. — The first totally indirect equipment tried consisted of
8 special indirect fixtures, these being white porcelain enameled
on steel, i$y2-'m. (39. cm.) in diameter and 5^2 in. (16. cm.)
deep (Fig. 16). Each fixture contained 3 36-watt tungsten
lamps mounted vertically. The fixtures were hung in a single
row down the center line of the ceiling, the tops of the reflectors
being 13 in. (33. cm.) below the ceiling. The spacing of the
units is shown on Fig. 21. The resultant illumination was uni-
form and of fairly good intensity, averaging 5.1 and 3.2 foot-
candles at normal and 85 per cent, voltage, for an energy con-
sumption of 1.47 watts per square foot. The effective lumens
per watt were 3.43 and the effective utilization efficiency was
46.3 per cent. The chief drawback of these fixtures was their
liability to catch and collect much dirt, thus materially reducing
their efficiency ; also, to obtain good distribution it was necessary
to hang them so low that they might be in the way of tall passen-
gers.
No. 2. — In order to get away from a low fixture in the center
line of the car, the next equipment tested consisted of 20 36-watt
tungsten railway lamps in indirect reflectors. These were mounted
236
TRANSACTIONS I. E. S. — PART I
3*,y^ ,Z? "O aw*? *o°j -i,j~oz'*e/Y
Fig. 16.— Installation of special indirect fixtures. Each fixture contains thtee 36-watt
tungsten filament railway lamps. Light distribution shown in Fig. 15.
Fig. 17.— Special installation of indirect lighting. Reflectors set in coves, ten on each
side. Ceiling rosettes for emergency lighting.
Fig. iS.— Indirect lighting from units on center stanchions and grab rails.
pigi i9— Lighting equipment finally adopted, consisting of fifteen 56-watt. bowl-frosted
tungsten filament railway lamps in white glass reflectors, supplemented by six 10-watt.
round bulb, all-frosted tungsten filament lamps for emergency lighting. Installation
finally adopted.
GOVE AND PORTER: CAR LIGHTING PROBLEMS 237
in two rows of ten each on the sides of the car, just above the
deck sill between the ventilators, as shown in Fig. 17. Five 10-watt
frosted lamps in rosettes were mounted on the ceiling for emer-
gency lamps. The 36-watt lamps were mounted horizontally with
their centers 7 ft. 4 in. (2.25 cm.) above the floor. The spacing
of the lighting units and the distribution therefrom is shown in
Fig. 22. The resultant illumination was of low intensity, aver-
aging 3.5 and 2.2 foot-candles at normal and 85 per cent, voltage.
The wattage consumption was 1.32 per square foot; effective
lumens per watt were 2.67 ; and effective utilization efficiency was
36.3 per cent. The main objection to this system was the prob-
lem of keeping the reflectors clean.
Xo. 3. — The last test was made on 12 94- watt tungsten rail-
way lamps in indirect reflectors and 5 10- watt emergency lamps
in rosettes, located down the center line of the ceiling. In order
to get maximum headroom for these reflectors and still have them
out of the way of passengers, special inverted cone-shaped con-
tainers for the reflectors were built into the stanchions along the
center line of the car (Fig. 18). Unfortunately the construction
of the car necessitated spacing the units rather far apart, so that
uneven illumination resulted. In addition to the bowls, smaller
inverted bowls were mounted on the horizontal grab rails, at
points shown in Fig. 23. Each of these contained 1 94-watt
tungsten lamp, making a total of 12 94-watt and 5 10-watt lamps
in the car. The average foot-candles were 8.5 and 4.7 at normal
and 85 per cent, voltage ; watts per square foot 2.01 ; effective
lumens per watt 4.21 ; and the utilization efficiency was 53.4 per
cent. Considerable difficulty would be experienced in keeping
this equipment clean and free from refuse.
The tables in the Appendix gives general summary of the
tests.
IMPORTANT CONSIDERATIONS.
In studying the tests to choose the final method of lighting, the
following condsiderations were carefully weighed :
General Effect and Appearance. — The general effect and
appearance of each system under test were judged by comparison
with present methods (in general) of car lighting for similar
service, i. e., with the use of tungsten lamps but without reflectors.
238 TRANSACTIONS I. E. S. — PART I
Under this item was also considered the effect of the distribution
of light on the various parts of the car.
Lack of Eyestrain. — In comparing the various systems tested,
the effect of the light on the eyes was particularly noted by a
large number of observers.
Base in Reading for Seated and Standing Passengers. — In
comparing the three methods of lighting — direct, indirect and
semi-indirect — particular attention was given to the possible
shadows thrown on reading matter of seated passengers, by pas-
sengers standing in a crowded car. In some cases it was found
that passengers could obtain proper light in any position ; in
others it was necessary for them to move in their seats, often to
uncomfortable positions, to obtain proper light.
Efficiency of System. — The efficiencies of the various lighting
systems tested differed widely. In some cases this was largely
due to the type of reflector used; in others to the position of the
reflector, shape of the ceiling, etc. In several tests it was evi-
dent that improvement could be made by changes. Should any
one system meet with particular favor in all other respects, it
was considered probable the efficiency could be raised by a more
detailed study.
Maintenance. — The question of maintenance was serious.
Some of the most desirable arrangements of reflectors and lights
were handicapped by the dust problem. With a large number of
small units this difficulty increases. Various methods of keeping
reflectors and ceiling clean were considered.
Pozcer Consumption. — In order to secure a reasonable oper-
ating cost, low power consumption was considered one of the
important factors. The indirect system of lighting required con-
siderably more power than the direct, while the semi-indirect
came between these two.
Depreciation. — The relative loss of reflecting power, due to
accumulation of dust on the various types of reflectors, was also
given careful consideration.
Emergency Lighting. — It was decided that sufficient light
would be obtained from the emergency lights to permit clearly
distinguishing people and various objects in the car with main
lamps extinguished.
GOVE AND PORTER: CAR LIGHTING PROBLEMS
239
24O TRANSACTIONS I. E. S. — PART I
RESULTS.
A thorough study of all these conditions finally led to the adop-
tion of a single line of 15 56-watt bowl-frosted tungsten railway
lamps down the center line of the ceiling, equipped with reflec-
tors as shown in Fig. 19, supplemented by 6 10-watt all-frosted
round bulb tungsten emergency lamps. This system was chosen
as the one containing the highest percentage of the desirable
factors — satisfactory illumination, low power consumption, low
maintenance and upkeep and pleasing appearance with the lamps
both lighted and extinguished.
The spacing of the reflectors was arranged to be symmetrical.
One unit was placed on each end bulkhead of the car to bring
up the illumination at these points. The emergency lamps were
placed in rosettes, one being located on the side wall over each
pair of doors. These lamps do not burn while there is power
on the line, but the instant that fails the emergency lamps are
automatically thrown onto a storage battery.
Fig. 19 shows the interior of the car as finally equipped. The
illumination averaged 5.94 foot-candles at normal and 3.85 at
85 per cent, voltage. The energy consumption was 1.44 watts
per square foot; effective lumens per watt 4.14; and the utiliza-
tion efficiency 50.6 per cent. These data are not comparable with
the other tests, due to the use of bowl-frosted lamps (instead of
clear), also a larger number and different arrangement of light-
ing units. Distribution curves are given in Fig. 24.
It was interesting to note that the low intensities of illumina-
tion, at stations 7 and 17 (Fig. 24), are opposite the entrance
doors, which are dark green, in comparison to the white finish
between doors. The curves were slightly high at stations 2, 3
and 4, due to the fact that the end lamps are located on the bulk-
heads considerably lower than the rest of the lamps in the car.
On the whole, the illumination is remarkably soft, even and
pleasing. It is not possible to note any unevenness with the naked
eye. The use of bowl-frosted lamps lowers the efficiency a little,
but also eliminates glare, even when looking directly up at the
lamp.
In addition to the general illumination there are other uses of
lamps, in connection with the signal system, which may be of
GOVE AND PORTER: CAR LIGHTING PROBLEMS
241
interest. There is a series circuit going through a contact on
each door in the car and on all doors in the train when more
than one car is used. This circuit also goes through two 2-candle-
power, 6-volt lamps located on top of the master controller near
the motorman. When all doors are closed one of the lamps lights
up and until this occurs it is impossible to start the train. Two
lamps are used for safety. If one fails the other is thrown in
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from the system of indirect illumination bowl-frosted railway tungsten lamps in white
shown in Fig. 18. Construction of car glass reflectors, and six 10-watt frosted emer-
necessitated spacing units rather far apart. gency in rosettes o\'er side doors. Installation
shown in Fig. 19. Equipment finally adopted.
circuit. The coupling of any number of cars together auto-
matically arranges the circuits so that the lamps on the con-
trollers, other than those on the two opposite ends of the train,
do not burn.
Block signal lights are located in the cab, i. e., instead of hav-
ing the signals aside of or above the track, as is usual ; the signal
is located in the car in front of and slightly to the right of the
controller. The signal consists of three lights — red, green and
yellow — each containing a 32-volt tungsten filament lamp of about
242 TRANSACTIONS I. E. S. — PART I
10 watts capacity. It is planned to use double filaments in these
lamps, so that when one fails the other will still be in operation.
If the signal is set to stop and is not obeyed, within a certain
distance, a warning whistle blows near the motorman, and if
the signal remains unheeded a certain further distance, the brakes
are automatically set. Coupling two or more cars together also
cuts out the signals in the cabs other than the two on the ends
of the train. A small 32- volt ^-candlepower tubular carbon lamp
is also installed over each air gauge.
The end of each car carries two classification lamps, 10-watt,
34-volt, on the roof (Fig. 5). Colored screens are used in these
to obtain the different destination indications. These lamps are
also automatically cut out between cars where two or more are
coupled together.
At the ends of each car, over the bumper, are located 4 10-watt,
40-volt, signal lamps back of lenses ; one above the other — two
on each side of the car. The upper is red and the lower white.
On the front end the white ones only burn; on the rear the red
only. Reversing the controller automatically changes these end
indications. These lamps also are cut out between cars of a
train.
GOVE AND PORTER! CAR LIGHTING PROBLEMS
243
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J44 TRANSACTIONS I. E. S. — PART I
BIBLIOGRAPHY.
Street Car Lamp Tests in Chicago.
Electrical Review and Western Electrician, Oct. 14, 191 1.
High Efficiency Lamps for Street Railway Service, by S. E. Doane.
Electric Railway Journal, May 4, 1912.
Test of Car Lighting with Mazda Lamps and Holophane Reflectors.
Electric Railway Journal, Sept. 28, 1912.
Tungsten Lamps in Car Lighting.
Electrical World, Oct. 5, 1912.
Car Lighting.
Electrical Traction, Mar., 1913.
Metallic Filament Lamps for Lighting Street Railway Cars.
Electrical World, Apr. 19, 1913.
Illumination of Tramway Cars.
London Electrician, Sept. 5, I9T3-
Economical Lighting of Street Cars, by S. G. Hibben and E. M. Smith.
Electric Journal, June, 1913.
Street Railway Illumination, by S. G. Hibben.
Electrical Review and Western Electrician, Oct. 4, 1913.
Street Car Lighting, by L. C. Porter.
Lighting Journal, Oct., 1913.
Improvements of Street Car Illumination.
Electrical Review and Western Electrician, Oct. 22, 1913.
Toledo Railways Adopt Improved Lighting for their Cars.
Electrical Review and Western Electrician, Oct. 25, 1913.
Argentine Tram Car Lighting.
Electrical Review, Nov. 7, 1913.
Illumination of Street Railway Cars, by L. C. Porter.
Electrical Review and Western Electrician, Nov. 8, 1913.
Electric Railway Car Lighting, by J. R. Cravath.
Electric Railway Journal, Nov. 15, 1913.
Improvement of Street Car Illumination.
Electrical Review and Western Electrician, Nov. 22, 1913.
Illumination of Street Railway Cars, by H. M. Ryder.
Lighting Journal, Dec, 1913.
Latest Practise in Street Railway Lamps, by V. L. Staley.
General Electric Review, Dec, 1913.
Modern Practise in Street Railway Illumination, by S. G. Hibben.
Illuminating Engineering Society Transactions, Dec, 1913.
Chicago City Railways' New Cars.
Electric Railway Journal, Dec. 20, 1913.
The Illumination of Street Railway Cars, by G. H. Stickney.
Electric Railway Journal, Dec. 20, 1913.
The Private Car "New Jersey."
Electric Railway Journal, Dec. 27, 1913.
GOVE AND PORTER: CAR LIGHTING PROBLEMS 245
The Illumination of Street Cars, by L. C. Porter and V. L. Staley.
Illuminating Engineering Society Transactions, Jan., 1914.
The 1913 Motor Cars of the Chicago. Railways.
Electric Railway Journal, Jan. 17, 1914.
Report of Western Association of Electrical Inspectors on Car Wiring.
Electrical World, Jan. 31, 1914.
Photometric Tests in Railway Cars, by L. C. Porter.
Lighting Journal, Apr., 1914.
Recent Progress in Street Car Lighting, by G. H. Stickney.
Electric Railway Journal, May 2, 1914.
Car Lighting Discussed by Experts, G. H. Stickney, C. O. Bond, P. S.
Millar, E. W. Hoist, J. Corning and others.
Street Railway Bulletin, May, 1914.
Storage Battery Lighting on New York Central R. R. Cars.
Electric Railway Journal, June 6, 1914.
Capitol Traction Company's Semi-steel Cars.
Electric Railway Journal, July 31, 1914.
Report of Committee of American Electric Street Railway Association —
Modern Car Lighting.
Electric Railway Journal, Oct. 24, 1914.
Car Lighting, Chicago, Lake Shore and South Bend Railway.
Electric Railway Journal, Dec. 12, 1914.
DISCUSSION.
Mr. T. W. Rolph : The authors of this paper have pre-
sented us with some extremely valuable data, and we are fortu-
nate in having this available for future use, in car lighting prac-
tise. There is an interesting point which I would like to bring
out, and that is in regard to per cent, utilization efficiency ob-
tained. I have a record of some car lighting tests, which were
conducted by the Indianapolis Traction Terminal Company, in
Indianapolis, in May of last year. There were recorded in a
paper presented before the Pittsburgh section last November by
Mr. L,. C. Doane.f The efficiency obtained with a prismatic
system, using 56-watt lamps, was 46.1; whereas with these tests
the efficiency obtained was 73.2. Similarly with a unit of medium
density opal,$ the efficiency obtained in the Indianapolis test was
40.2 ; while the efficiency here is 68.7. This difference is due to
the finish of the cars. We have obtained in the tests recorded
here, probably the highest utilization efficiencies that have ever
t Modern Street Car Lighting, Trans. I. E. S., vol. X, p. S2, (1915).
I "Sudan" glass.
246 TRANSACTIONS I. E. S. — PART I
been obtained in general commercial work. The subway people
are to be congratulated on obtaining efficiencies very appreciably
beyond those which have been obtained in other classes of light-
ing.
Mr. S. G. Hibben : To the companies which have made such
a thorough investigation of car lighting in this instance, there is
more than ordinary credit due, both for the standard and detail
of the work, and also because a good deal of this car lighting is
still pioneering. The engineers of this investigation and the
authors of the paper deserve a large measure of thanks.
The night before last in Pittsburgh at a section meeting of the
society certain men, who are supposed to know a great deal about
car lighting equipment, made the statement that in several cars
where the tungsten lamp had been tried in conjunction with
globes, the illumination was poorer and of less amount than when
bare unshaded carbon lamps were used. On looking into that
pessimistic statement, I found that the experience of those par-
ticular men was that the lamps had been used in prismatic hemis-
pheres against the ceilings of the cars. The comparative inef-
ficiency of such glassware used thus, and its dustiness, was a very
unfair argument against the general use of tungsten lamps and
reflectors.
Some criticisms that have been made against the economy of
tungsten lamps came from the fact that the lamps were stolen, and
not broken, and that loss might be mentioned here in connection
with the comparison between center-deck and side-deck lighting.
I have experienced cases where lamps placed low along the side
decks were stolen quite often. The lamps along the center deck
were out of reach and did not disappear so fast. I believe these
losses may be reduced through the use of the marine type socket
or receptacle. The coiled spring into which the lamp base screws
not only prevents the lamp from shaking out, but also prevents
it from being easily unscrewed and stolen.
Concerning the glass reflectors, I want to call attention, in the
first place, to the inadvisability of using any blown glass reflec-
tors on which many manufacturers leave a ground or rough edge.
On account of the method of manufacture, the blown reflectors
in their first stage, are completely closed, and afterwards are
CAR LIGHTING PROBLEMS 247
broken off at the bottom, and ground straight. If this roughed
edge is not fire-polished, it in time will gather dirt and appear
as a dark edge.
There is just one experience I have had in the failure from
breakage of glass reflectors in car lighting service where, under
very extreme conditions of rough service, several shades which
were poorly held by the glass lip only, were broken around the
upper part. The type of holder which has the inner flange will,
of course, prevent that sort of breakage.
If the ceiling finish of the tested car as herein reported was
polished or glossy, the results from the indirect or semi-indirect
units might not be as good as in the case of depolished ceilings.
Light from the curved-plate units especially would be directed
against the sides of the car by specular ceiling reflection, and
would be largely lost.
Regarding cleaning costs, I would like to get some more
figures on that subject if there are any available. After a year
or two, about the best data I have on hand shows an expense of
about 7 cents to 10 cents per unit per month for cleaning ex-
penses. That I believe involves wiping the reflector, dry, three
times a month and washing it with water once a month. If the
reflectors have any kind of crevices, as in the case of prisms, or
if the elaboration is a design with horizontal lines, the expense
of cleaning may be considerably greater.
These cars are I suppose arranged with three circuits of lamps.
In case of one lamp failure the illumination is cut down to
approximately two thirds of its former value, which still is, I
believe, sufficiently high. To those unacquainted with some other
practises, fifteen 36-watt lamps for a car are sometimes consid-
ered too many, and arrangements have been made with either
two circuits of five lamps each, or one circuit of five larger
lamps, and using a selector switch which will short-circuit a
burned-out lamp, and simultaneously place in the circuit an
auxiliary lamp. One good feature of this arrangement is that by
using a three-point, or three-way switch, interurban cars which
load and unload at definite stations can be lighted at both plat-
forms or at either platform, while one regular unit in the center
of the car would be temporarily cut out.
4
248 TRANSACTIONS I. K. S. — PART I
There is at least one other system of wiring with features of
special interest, where there are ten no-volt lamps in series, on a
circuit of 1,100 or 1,200 volts. One of the peculiar features in
this case, is that the large or mogul base lamps are necessary,
because with the failure of one lamp the open circuit voltage
across the base of this lamp would be that of the line, and would
tend to arc over the distance separating the contact points of
ordinary Edison base lamps.
Mr. G. H. Stickxey: This paper presents a more complete
and comprehensive set of car lighting data than has heretofore
been available. The fact that the different lighting arrangements
have been tried out in the same car and under the same conditions
gives unusual value to the comparative results. In the past it
has been impossible to eliminate variations due to difference in
shape of cars, finishes, window areas, etc. We are certainly
indebted to the New York Municipal Railway Corporation and
Brooklyn Rapid Transit Company for giving out the information.
I know they have hesitated to do so lest it work injury or injus-
tice to excellent types of equipment which for their conditions
were not so suitable as some other types. I believe this factor
had something to do with the omission of more general conclu-
sions. The practical conclusion of the tests is, of course, indi-
cated by the lighting plan selected. The simple presentation of
the facts, as given in this paper, is a pleasant contrast to some
papers in which authors draw sweeping conclusions apparently
not warranted by the data presented.
The effect of the light finish of cars, brought up by Mr. Rolph,
is exceedingly important and often does not receive sufficient
attention from railway companies. A light finish in the lower
part of the car is not especially advantageous and is easily soiled.
In the upper part, however, a light finish not only helps to econo-
mize the light, but adds to the diffusion and evenness of distri-
bution.
One of the serious problems of applying the reflector method
of car lighting was that of securing a satisfactory holder for
the reflectors. The holder shown here to-night has more good
features than any other I have seen. It has seemed objectionable
to some to use the 2>4 in. fitter rather than the more common
CAR LIGHTING PROBLEMS 249
2^4 m- 1 but, as both prismatic and white glass reflectors with
this fitter are available, this would hardly seem to me serious ;
while the other advantages which can be obtained with the larger
fitter would seem to me to be important. The holder clamps the
reflector in such a way that it cannot possibly fall unless com-
pletely shattered. The glass is supported from below independent
of the flange. The larger opening permits the use of stronger
porcelains on the socket and therefore provides safer insulation.
The large wiring space makes it more convenient and safer to
wire with the heavily insulated cables required on street railway
circuits.
A spring socket protects the lamp from excessive vibration.
While this does not entirely prevent stealing of lamps, it renders
their unauthorized removal more difficult.
Most of the lock-sockets with which I am familiar cannot be
used with reflectors.
Very little trouble from stealing has been encountered as far
as I am able to learn. Practically all lamps stolen are taken by
employees when the cars are in the car houses. It would, there-
fore, seem that the best way of overcoming it would be through
discipline of employees, just as in the case of an office or indus-
trial establishment.
Mr. Frank M. BrinckerhofF: This paper gives very inter-
esting details of the tests. One feature, always difficult to decide,
is the commercial value of any lighting system. It is hard to
place a value on the lighting of passenger cars, except as it affects
the traffic of the road. If two car lighting methods are in use
on the same train, it can easily be noted that the cars which are
improperly lighted carry but few passengers as compared with
cars which are better lighted, and one can thus possibly place a
relative value on the lighting systems. The New York Municipal
Railway cars are to be in the subway about one third of the
entire time of their operation; therefore, the lighting problem is
of considerable interest, during the day as well as during the
night. Of course, with the ordinary trolley car, operating on the
surface and requiring electric lights but a few hours of each day,
250 TRANSACTIONS I. E. S. — PART I
the lighting is of less importance than in subway service where
it is an all-day proposition.
One possible commercial view that could be taken of the light-
ing problem is the effect on the advertising cards. Now, that
may sound rather odd, but in a great many cars, especially in
subway service, where the traffic is very heavy, the income from
the rental of advertising space is very considerable. At times
the cards and color effects are made very attractive to catch the
attention of passengers. The advertiser is undoubtedly influenced
by the lighting which is thrown on his advertisement.
Chairman : You will notice in all these cars that they all have
full windows just as passenger coaches ; it has always seemed to
me a considerable waste of light to have the same windows in
the cars that you would use with daylight cars. There seems to
be no good reason why the sides of the cars should not be fin-
ished with white enamel and just a narrow window near the top
of the present glass.
Mr. Frank M. Brinckerhoff: The reason for windows in
subway cars is to enable the passengers to see out at the stations ;
so that passengers can see at what station they are. People fre-
quently have trouble in determining their station. The seated
passenger needs the window to look out just as much as the
standing passenger does, and you will find the windows of the
subway car about suitable for the purpose.
All the ceilings have been rubbed flat finish to take off the
high gloss ; this surface eliminates a great deal of glitter and
affords a much more pleasing illumination.
Chairman : Peculiar color combinations are used on the sub-
way advertising cards; yellow and orange are used in certain
words or lines for emphasis. Has an advertiser ever complained
that these cards are not as conspicuous under artificial light as
he thinks they should be? These cards are probably designed
and approved under daylight, and it cannot be expected that
certain color combinations will be as striking under artificial
light as they would be in daylight.
Mr. Frank M. Brinckerhoff: I do not think the color of a
card has ever been discussed, but the color of the car finish has.
I have never heard of a complaint by an advertiser that his pecu-
CAR LIGHTING PROBLEMS 25 I
liar color combination was not properly illuminated; I do not
think that I have ever heard of that being brought up; but, of
course, the color combination of the car itself has a great deal
of effect, or rather it influences the appearance of the cards. A
good frame around a picture brings out and enhances the picture ;
just so, this moulding around the advertising card either pro-
duces an attractive effect, or detracts from the appearance of the
cards. For example, if green moulding is carried along beneath
the entire row of advertising cards, it gives it a dignity and bal-
ance that is rather attractive. If advertising cards are mounted
against a flat white background above and below, it rather detracts
from their color scheme. I have never heard of the color of the
card being affected by the illumination ; but I can easily see that
it could do so.
Mr. Young: As to the elaboration on the glass to be used,
I think every one is coming more and more to an absolutely
plain surface on any lighting glassware that they use. It is quite
easy to get up a line of glassware comprising reflectors, hemis-
pheres, etc., with an elaboration that is quite intricate; but
it is quite hard to get up a piece of glass with a simple
elaboration. I have been at it a good many years, and I know
what it means. Recently, there has been marketed a line, as you
would say, of absolutely plain glassware as shown in Fig. 12.
The disk, or fixture shown is w-ithout elaboration. There has
been some discussion to-night in regard to the collection of dust
on reflectors, etc. The glassware shown in Fig. 12 could be more
easily cleaned than a shade ; the glass can be cleaned with a piece
of chamois ; or it can be cleaned with a dry rag, provided the
atmosphere is not greasy; in which case, of course, the glass
would collect grease and would have to be washed.
Mr. L. C. Porter (In reply) : One speaker asked what fac-
tors were against the special turnip-shaped lamps without re-
flectors, and against the indirect system. One of the chief draw-
backs of these two systems was the lack of headroom in a car
either to get an indirect fixture or a special lamp with opal on
the bottom sufficiently low from the ceiling so that it would light
the ceiling fairly evenly, instead of just throwing a little spot of
light on the ceiling. To do this it was necessary to put the lamp
-'D-
TRANSACTIONS I. E. S. — PART I
or fixture so far down that it would necessarily be in the way of
tall passengers, particularly those wearing opera hats. One of
the other chief factors against those two systems was the col-
lection of dirt, etc.
In regard to light distribution, it is true that the outside dis-
tribution curve is probably the most important one, but even with
passengers facing sideways in the car it was found that, under
average conditions, they held their papery at least two feet out
from the side of the car, which brought them within the range of
the distribution curve shown.
You will note that so far car lighting problems have dealt
with fitting the lighting to cars at present in service — that is, cars
already designed.
In one of the tests described in the paper, you will find that a
special ceiling insert was made to see if the lighting could be
improved. This opens quite a field; in other words, why should
not the roof of the car be designed to fit the lighting?
Mr. Frank M. Brinckerhoff: If a car could be designed
with a cross section similar to that headlight that we have looked
at this evening, it would insure the most even distribution of
light ; in other words, if the roof of the car could be given a
parabolic form and the lamps could be placed on the exact focal
center of the parabola, an absolutely even distribution of light
over the entire width of the car could be obtained. The height
of the New York Municipal Railway cars made it necessary to
take a certain definite width, with the result that it is impossible
to place the light sources exactly as we would have desired ; it
was necessary to accept a compromise position. The distribution
of light finally secured is about as good as can be obtained in a
car of this height and width.
IVES AND KINGSBURY : HETEROCHROMATIC PHOTOMETRY 253
ADDITIONAL EXPERIMENTS ON COLORED ABSORB-
ING SOLUTIONS FOR USE IN HETERO-
CHROMATIC PHOTOMETRY.*
BY HERBERT E. IVES AND EDWIN F. KINGSBURY.
Synopsis: This paper is a continuation of one recently presented
under a similar title. It describes a blue solution which used over a
standard carbon lamp duplicates the color of lamps of higher efficiency.
The photometric calibration of this solution is given. Simple equations
have been developed to represent the transmission of both this new solu-
tion and the previously described yellow solution.
In a previous paper1 before the Illuminating Engineering So-
ciety we have described a yellow absorbing solution which can
be used in varying concentrations to eliminate the difference in
color between black bodies at different temperatures. We present
herewith an account of a blue solution of similar properties, which
may be used over the present carbon incandescent standards, to
produce with them all the incandescent lamp colors up to the most
efficient lamps now obtainable. In the previous paper details are
given as to the mode of use of the solutions and upon the method
of calibration. The present communication may be considered
as a continuation of the other, containing only matter not therein
included.
Constitution of New Blue Solution. — The blue solution has the
following composition :
Nickel ammonium sulphate 50 gr.
Ammonium sulphate 10 gr.
Ammonia 0.90 gr 55 cc.
Water to 1 liter of solution
Dilute with water containing 10 gr. ammonium sulphate per
liter.
The solution should be used as fresh as possible, because on
standing it slowly dissolves the glass of the containing vessel, and
* A paper read at a meeting of the Philadelphia Section of the Illuminating Engineer-
ing Society, March 19, 1915.
The Illuminating Engineering Society is not responsible lor the statements or
opinions advauced by contributors.
1 Ives aud Kingsbury, Experiments with Colored Absorbing Solutions for Use in
Heterochromatic Photometry; Trans, I. E. S., vol. VIII (1914), p. 795.
254
TRANSACTIONS I. E. S. — PART I
because alkaline solutions such as this are inherently less stable
than acid solutions like the yellow one.
Calibration. — The same method of calibration was used as
before. One advance lay in the fact that our average observer
was obtained from the mean of sixty-one instead of twenty-five,
as in the earlier work. The working' group from whom the
seven observers were taken was only in part the same as before,
but, if the method of selection is reliable, their mean result should
be the same as that of the similarly selected group used in the
yellow solution work, since the mean value for the test green
light was little affected by the inclusion of the larger number of
observers now used in establishing the standard eye.
100
90
80
.70
| 50
?40
30
.20
.10
fll L-i_
10 .20 30 10 SO 60 70 80 .90 100
CONCENTRATION
Fig. i.— Transmission of blue solution. Equation of curve: logi0T
\
Jy
\^
s
X
z
z
N
V
s
s
z
g
3
S
s
z
f*^
u
1
%
5
539C'-
The observations are plotted in Fig. I, on which are also shown
the approximate concentrations called for by typical illuminants.
Temperature Coefficient. — An undesirable feature of the yellow
absorbing solution is the existence of a pronounced temperature
coefficient, making it imperative either to work at the temperature
used in calibrating or to apply corrections.
We find the blue solution to have practically no temperature
coefficient over the range of temperature to be expected in the
laboratory This is a very fortunate thing, especially as the field
IVES AND KINGSBURY: HETEROCHROMATIC PHOTOMETRY 2
33
of usefulness of the blue solution may be expected to be much
greater than that of the yellow.
Spectral Transmission. — Fig-. 2 shows the transmission through
the spectrum, as measured on the spectrophotometer, for the
100 per cent, solution. When plotted in terms of log. absorption
against i/A an approximation only to a straight line results, as with
the yellow solution. This means that the color match obtained
by using the solution is a subjective one and will not hold abso-
lutely with observers of abnormal color vision. This divergence
from actual identity of the two compared spectra is, however, too
small, we believe, to cause trouble in practical work. We find
as well that Beer's law does not hold, so that the concentration
6
in
2
Z. ,
< '
a.
1-
.2
/
'
A
3 4
5 .5
3 .5
WAVE-
5 .6
l-ENGTH
3 .6
5 .70
Fig. 2. — Spectral transmission of 100 per cent, blue solution.
necessary for any particular case cannot be obtained by experi-
ments on thickness. Trial of various concentrations is necessary.
Comparison of Results Using Yellow and Blue Solutions. —
The yellow solution when used on the test side performs the
same color difference eliminating function as the blue solution on
the comparison lamp side.
It is a matter of interest to know how closely the value to be
assigned by using one solution agrees with that from the other.
This constitutes a test of the method of calibration. If the
method is reliable and self-consistent the same value should be
obtained upon measuring a high efficiency lamp by the use of
either solution.
This point was tested by the measurement of a type "C" tung-
sten lamp, efficiency 0.65 w. p. c, against a 4-watt standard. The
256 TRANSACTIONS I. E. S. — PART I
requisite concentration of the yellow solution was determined by
the use of the wedge cells described in the previous paper; that
of the blue by several trials. The relative intensity of the two
lamps was then found to be the same to about y2 per cent, or
within the errors of photometric setting.
This test, involving as it does two different series of measure-
ments made several months apart, with largely different groups
of observers, shows clearly the reliability of the photometric pro-
cedure.
Mathematical Expressions for the Transmission Curves. — In
order that these colored solutions may not only be made up but
also used from written specifications, it is desirable that their
transmission be expressible in some simple mathematical form.
This we find to be possible.
In the case of monochromatic light the equation connecting
transmission with concentration is of quite simple form, namely,
T = T0eac
where T is transmission, T0 is the transmission for zero concen-
tration, e is the base of the natural system of logarithms,, a is a
constant and c is concentration. In the present case T0 is unity,
so that the relationship may be written simply :
T = kc
or
log T = ck'
Now, we are not dealing here with monochromatic light, but it
is well known that over considerable ranges of color change in
black body illuminants the total change in intensity is very closely
the same as the change of intensity for a certain single wave-
length.2 We should, therefore, expect the above equation to
hold over a fairly large range of concentrations. When, how-
ever, this range is exceeded the deviation is slow and can be
taken care of by a slight modification of the simple law. Thus
we find that over the whole range of concentrations called for by
the present practical illuminants the transmissions of our solu-
tions are represented with extreme accuracy by equations of the
form
log T = c*k
- Ives. II. B.| Note on Crova's Method of Heterochromatic Photometry; Physical Review,
XXXII, 3, Mar. 1911, p. 316.
IVES AND KINGSBURY: HETEROCHROM ATIC PHOTOMETRY 257
where x is a number only slightly differing from unity. The
actual equations for the yellow and blue solutions are as follows :
Blue solution on comparison lamp side • • -log10 T = — o.539^I-°3
Yellow solution on comparison lamp side-tog10 T = — o. 245^-9
Yellow solution on test lamp side log10 T = -j-o. 366^1 -°5
where T and c are expressed in decimal fractions of unity (i. e.,
20 per cent, transmission or concentration is expressed as 0.20).
The curves represented by these equations lie everywhere distant
1.40
135
130
125
ST 120
S
z 115
1 IIC
2
u. 105
3 100
g .95
I 90
z
<c
.80
75
.70
{ i
\\
i
|[\ !
§i ^\S
\j
s!
s\
SOLUTION ON COMPARISON
1 LAMP' SCl
1 ||K
%
I 1
\?l
z
si
SO
UTI0N
0NTE
- lam
SIDE
.
SO .40 30 .20
.10 0 ID
CONCENTRATION
.20 .30 .40 50
Fig. 3.— Transmission of yellow absorbing solution at 20 deg. C. Equations of curve:
comparison lamp side, log10T = — 0.245C9; test lamp side, logi0T = 0.366c1"*5.
from the experimentally determined points by no more than the
uncertainty of the experimental work. The full line in Fig. I
has been drawn with the aid of the first equation, and in Fig. 3
the data on the yellow solution have been reproduced along with
the curves represented by the second and third equations.
DISCUSSION.
In the previous paper we dealt rather insistently on the diffi-
culties of working with absorbing solutions. Among these dim-
258 TRANSACTIONS I. E. S. — PART I
culties the care of the glass tanks and the complications caused by
the temperature coefficient figured prominently. In the light of
our more extended experience we now feel it permissible to speak
somewhat more favorably of this method. We have found that
the absorbing tanks in the form developed in the course of the
investigation maintain their similarity in spite of nearly con-
tinuous use for months. The new blue solution with its freedom
from temperature coefficient removes another objection. And,
finally, the possibility of representing the transmissions by simple
equations places these solutions squarely in the category of
primary color standards, entirely reproducible from specification
at any time or place. By their careful use all laboratories can
insure a high degree of uniformity and agreement in measure-
ments involving the commonest type of color differences, once
agreement has been reached on the values to be assigned to the
transmissions. The scale upon which we have determined these
transmissions is based upon a careful study of photometric
methods and is, we believe, entitled to most serious consideration
for adoption as standard.
IVES AND KINGSBURY! COLOR VISION 259
METHOD OF CORRECTING ABNORMAL COLOR
VISION AND ITS APPLICATION TO THE
FLICKER PHOTOMETER.*
BY HERBERT E. IVES AND E. F. KINGSBURY.
Synopsis: A study is made of the manner in which the spectral
luminosity curves of individuals differ. It is pointed out that when the
flicker photometer is used any observer can be corrected to normal by the
interposition of the proper absorbing medium over his eye. Practical
approximations to such absorbing media are developed and tried. By
their means color-blind observers are made to read substantially the same
as normal.
Various investigations on the spectral luminosity curves of
individuals of normal and abnormal color vision have clearly es-
tablished that these curves differ from individual to individual.
The differences are small between those who would be classed as
of normal vision, but of increasing magnitude as observers are
included of the various types of recognized color blindness. This
fact is illustrated by the luminosity curves of normal and color-
blind observers shown in Fig. i.
Now, an individual of abnormal color vision suffers from two
characteristic disabilities, both probably due to the same funda-
mental defect. One is the distortion of color values, the other the
distortion of luminosity values. These two disabilities are of
differing gravity' to an individual, depending upon the use he
makes of his eyes. If his work demands the discrimination or
harmonizing of colors, then inability to differentiate hues is suf-
ficient to disqualify him. If, however, his work involves the
measurement of luminous intensity the fact that one color has to
his eye the same quality as another embarrasses him not at all,
but the fact that the different colors do not have the same relative
intensity as to a normal eye is a serious handicap.
One of the present writers suggested some time ago1 that an
abnormal eye might be corrected for purposes of photometry by
* A paper read at a meeting of the Philadelphia Section of the Illuminating Engineer-
ing Society, March 19, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
1 Ives, Discussion of a paper by Fabry ; Trans. I. E. S., June, 1913, p. 320.
2(5o
TRANSACTIONS I. E. S. PART I
the aid of an absorbing screen which would reduce the intensity
of certain portions of the spectrum. Dr. Louis Bell more re-
cently2 has suggested that in certain types of abnormal color
vision, where one sensation is only partly deficient, correcting
glasses might, in restoring the balance between the different parts
of the spectrum, enable the wearer to see colors in their normal
hue relationships. This latter possibility of course only applies
where all three fundamental sensations (in the Young-Helm-
holtz sense) are present to some degree. The photometric possi-
bility is equally good whether the observer perceives color or not,
provided he sees something in all parts of the normally visible
spectrum. That is, even an individual who sees the spectrum as
Fisr. I. — Spectral luminosity curves of three normal and one totally color-blind
observers. (Three "normal" from data of Ives; color-blind from measure-
ments by Bender.)
a mere colorless band should be able to obtain normal photo-
metric results once the luminosity curve of his spectrum is nor-
malized.
The type of observer just mentioned would in fact have a cer-
tain advantage in ordinary direct comparison photometry, be-
cause he would not be distracted by the difference of quality
which causes the fundamental difficulty in colored light pho-
tometry. So serious is this distraction that definite and satis-
factory results can be obtained in colored light photometry only
by the use of the flicker photometer. Consequently in this paper,
1 Bell, L.. Types of Abnormal Color Vision ; Pioc. Amer. Acad., 50, pp. 3-13, May, 1914.
IVES AND KINGSBURY: COLOR VISION 26l
which deals chiefly with the application of this correction method
to photometry, the flicker method alone will be considered, it being
understood that the method of correction should be equally ap-
plicable to direct comparison photometry were this latter a prac-
tical means of precision measurement.
The peculiar applicability of the flicker photometer to this
proposed method of correction lies in its entire elimination of
the question of quality. The system composed of the flicker
photometer and the eye is a physical null instrument, in which
the eye acts merely as the sensitive detector of a lack of balance
in which color or quality plays no part and only the luminosity
differences remain. Such a system may be subjected to the
action of colored absorbing media in exactly the same way as
can a thermopile or a photo-electric cell, with a similar alteration
of its spectral sensibility curve.
Once this fact is clearly recognized the possibility of altering
a known individual luminosity curve into a normal one by ap-
propriate colored absorbing media is obvious. It is, however,
possible that the production of a correcting screen for each in-
dividual might be a task of great difficulty. How much do in-
dividuals differ? Can an average type of correction be worked
out practically? If so what is its field of successful application?
These questions were the object of the investigation here re-
ported.
I.-THE DIFFERENCES BETWEEN INDIVIDUAL LUMINOSITY
CURVES AND THE CORRECTIONS CALLED FOR.
Some forty spectral luminosity curves, obtained by the flicker
method, are available for study, obtained by Ives and by Nutting,
and probably half as many more, obtained under somewhat dif-
ferent conditions by workers with the Lummer-Pringsheim
flicker photometer. For the present purpose a single group is
sufficient, and for this the curves obtained by Ives are used;
Nutting's lead to exactly similar conclusions, as do probably also
the other curves quoted. In Fig. I are shown several luminosity-
curves selected from the larger group of 18 3. In Fig. 2 these
are plotted in percentages of the mean at each wave-length. From
3 Ives, The Spectral Luminosity Curves of the Average Eye; Phil. Mag., Dec. 1912,
P- §59-
262
TRANSACTIONS I. E. S. PART I
these selected curves it is apparent that deviations from the mean
are of two kinds: First, that characterized by a uniformly
changing deviation of the type represented by the equation
I = — -\- B, and, second, small localized variations from this
A
simple type of variation, resulting in more or less extended con-
S6 58
WAVE-LENGTH
Fig. 2. — Characteristic deviations from normal spectral luminosity curve,
and effect of applying correcting medium.
cavities or convexities in the plotted lines. These latter, which
are in most cases undoubtedly real and not errors of observa-
tion, are due probably to individual differences of pigmentation
of the fovea and similar causes, superposed on the main basis of
difference, namely the relatively different proportion of the three
color sensations. In Fig. 3 we have plotted the average deviation
>
-.
, ^^_^~
»-
■■—■J.
^_
8 5
G 5
2 .5
4 .5
6 a
8 i>
0 i
2 t
4 i
M
WAVC - LENGTH
Fig. 3.— Average deviation from normal luminosity curve of
red-sensitive and blue-sensitive groups.
from normal of all those observers lying clearly on the blue side
of the mean and all those lying clearly on the red side. It is at
once seen that the small localized irregularities are largely ironed
out and that the average type of deviation from normal consists
IVES AND KINGSBURY: COLOR VISION 263
in the simple gradual variation with wave-length represented by
the equation already given.
It may be stated without further discussion that an average
type of corecting medium would be one whose spectral trans-
mission is the reciprocal of the average deviation just shown, as
T = — \- b. Such a medium with varying values of a and b
A
should correct the main deviation from normal vision. At the
same time such an average correction cannot fit the smaller in-
dividual differences.
At this point it may be remarked that this study might have
been carried through on merely one or two individuals whose
luminosity curve would first be accurately determined, exact cor-
rection screens then being developed, and their performance
examined. We have not done this because the well established
physical characteristics of the flicker photometer already men-
tioned tell us in advance that such an individually worked out
correction would be exact. The labor, however, of working out
individual screens for every member of a laboratory staff would
make the scheme at once a dubiously practical one. Our interest
has, therefore, been in studying the possibility of adapting this
method in such simplified form as to make it practical. We
have accordingly worked out an average correcting medium and
have investigated the extent of its usefulness.
tt— THE PERMANENCE OF THE COLOR CHARACTERISTICS
OF INDIVIDUAL OBSERVERS.
Will a correction once found adequate always be so? This of
course depends upon the permanency of the luminosity curve.
In previous papers on the flicker photometer, evidence has been
presented that an observer's characteristics are permanent. In
the course of nearly a year's continuous use of the photometric
method advocated by us, we have accumulated a mass of data
from which very definite information on this point is available.
We have arranged some of these data graphically in Fig. 4.
At our disposal were the following sets of observations : two
series of readings on monochromatic green light compared with
5
264
TRANSACTIONS I. E. S. — PART I
the light of a "4-watt" lamp*; four series of measurements on
a special yellow solution which in varying concentrations takes up
the color differences between incandescent lamps of various effi-
ciences5 ; two series on a blue solution of similar characteristics8,
which ultimately proved unsatisfactory (A) and two on the
satifactory solution (B) ; two sets on a pair of test colors used in
the selection of groups of observers for colored light photometry.7
These are plotted in such manner that measurements on the blue
side of the normal fall above the axis of abscissa, those on the
M0N0-
;HR0MAT
GREEN
: BLUE SOLUTION A
-t .1 .4 .J .2 .1 0
YELLOW SOLUTION
.1 .2 ,1
TEST
COLORS
BLUE SOLUTION B
-5 JL ,3 A ,.l ..0
**
x
■~i.
1 +
-J —J- i _ __ £ Jt^ x^
■JlfUj^
^^?--^
f«
0
X
+•
s • •
°,
§
2.
I
•/_*-*-* *~r
jQl&i**
II
j-*-;-t"*~*
'
1 1
5«
3.
X
. *xl X J
• .
■ 'i
1
■ _*—»— "-J-*-*""
-?-§^-<^-"i¥;
II
'
.■*
44
4
it
L ■ x x • •
'
X *
*«
"
1
Fig. 4. — Photometric history of four observers.
yellow below. The ordinates are the percentage deviations from
the mean. In the case of the yellow and blue solutions the
4 Ives and Kingsbury, Measurements with the Flicker Photometer on a Monochro-
matic Green Solution ; Physical Review, March, 1915, p. 230.
6 Ives and Kingsbury, Experiments with Colored Absorbing Solutions for Use in
Heterochromatic Photometry ; Trans I. E. S., vol. VIII, p. 795 ; 1914.
• Ives and Kingsbury, Additional Experiments on Colored Absorbing Solutions for
Use in Heterochromatic Photometry ; Trans. I. E. S., 1915.
'• Ives and Kingsbury, On the Choice of a Group of Observers for Heterochromatic
Measurements; Trans. I. E. S., 1915.
IVES AND KINGSBURY: COLOR VISION 265
greatest color difference is to the left, decreasing to a very small
color difference at the right. The observations on these solutions
should, therefore, in general converge toward the axis, as they
do. The scattering of these points is not to be taken as evidence
of lack of sensibility of the photometric method, as all kinds of
possible errors influence the results.
With very few exceptions our observers have maintained
throughout their positions relative to the mean. This is strikingly
shown in the case of observers I, 2 and 3, whose observations
practically all fall on one side of the normal line. We have
found but one actual reversal of position in the case of the
monochromatic green reading by an observer, not here shown.
The first reading was made upon a green absorbing solution
which afterwards proved of unstable composition so that even this
case is not clearly proven. Fluctuations of color vision do how-
ever undoubtedly occur, caused for instance by exposure to the
eyes to intense light, by working with colored light, as in the
spectrophotometer, etc., and these show up, as they should, in
the flicker photometer measurements. But apart from these
there is no doubt that an individual's spectral luminosity curve
is as much a personal characteristic as, for instance, the con-
figuration of the eye-ball, for which we prescribe spectacles.
An interesting piece of information is obtained by studying the
relative amounts of the deviations from normal with the different
kinds of color differences. These are not entirely parallel with
different observers. Thus the percentage deviation from the
mean of observer 4 is, with the very saturated colors of the first
and last columns, quite large, but with the less saturated colors of
the middle columns his readings average very near normal. On
the other hand the more extreme observers, such as numbers
1 and 2, show up consistently away from the mean, although
measuring the monochromatic green no further off than observer
4. These differences are clear cases of those localized differences
in the luminosity curves already noticed. We may from them
expect that no average type of correction will cut finely enough
to take up with great success rather small differences in color
vision, or do more with abnormal observers than bring them near
normal.
266
TRANSACTIONS I. E. S. PART I
III.— THE PRACTICAL DEVELOPMENT OF CORRECTING
MEANS APPLICALBLE TO THE AVERAGE TYPE
OF DEVIATION FROM NORMAL.
The absorbing media which we sought, to be used over the eye
for correcting the luminosity curve, were two, a generally blue
one, and a generally yellow one, each having a transmission
represented by a straight line from one end of the visible spec-
trum to the other, and capable in varying concentrations of
giving all ordinarily necessary corrections without serious depart-
ure from that type of transmission. Of course the exact attain-
"H\
•
»■»**""
/
/
•
/
/
/
\
3-^
/
i
.50 54 5) K
WAVE-LENGTH
7C^
Fig. 5.— Spectral transmission of correcting solutions; full line,
blue solution, dashed line, yellow solution.
ment of the desired characteristics is hardly to be expected. The
media which we finally selected after considerable experimenta-
tion are for the blue:
Cupric sulphate 2.0 gr.
Ammonia (0.90 gravity) 200 cc.
Add water to make 1 liter of solution. (Dilute with water
4 parts, ammonia I part.)
and for the yellow :
Bayer's Fast Brown, 0.025 gram per liter of water.
The spectral transmissions of these are shown for 100 per cent,
concentration in thickness of 5 mm. in Fig. 5. It will be seen
that they approximate fairly closely to the required charac-
teristics, especially through the middle, of the more important
part of the spectrum.
The result of applying the 60 per cent, solution to the lumin-
osity curve A. W. of Fig. 1 is given in Fig. 2. By the use of
the correction the general slope of the curve is removed, whereby
IVES AND KINGSBURY: COLOR VISION
267
it is reduced to the same class as those possessing merely localized
irregularities.
The practical means for applying the correction consisted of
small glass tanks, made very simply by drilling one centimeter
diameter holes in pieces of plate glass 5 mm. thick and two and
one-half centimeters square, riling a groove for filling and fasten-
ing thin glass faces on with paraffin. These were slipped over
the eye-piece of the flicker photometer.
We have worked with liquid solutions as simpler for the ex-
perimental work. Doubtless colored glasses could be found
which would serve. These could be used in the form of wedges.
IV.— THE EFFICACY OF THE CORRECTING SCHEME ON
A GIVEN COLOR DIFFERENCE.
In order to determine the amount of correction needed by the
various observers at our disposal, we have made use of the test
^
/
<
:~Z
~~~~~
»---
•
/
^
■
r-"
■
20 40 60 80 100%
CONCENTRATION OF CORRECTION SOLUTIONS
Fig. 6. — Effect of color vision correcting solutions on test
color intensity ratio with four observers.
colors by which we select a group of observers for heterochro-
matic measurements7.
Each observer measured the ratio of these two colors, which
should measure equal to a normal eye, then with progressively
greater concentrations of the correcting solution which was indi-
cated as necessary. With each concentration a different ratio of
the two intensities was obtained. The series of points thus found
were then joined by a line the intersection of which with the axis
indicated that exact correction demanded. These lines were found
fortunately to be straight. In Fig. 6 are plotted the results ob-
268 TRANSACTIONS I. E. S. — PART I
tained by four observers. It is evident that in the case of a given
color difference the method of correction is perfectly definite.
An interesting fact, in accordance with the known types of
differences in the luminosity curves, is that individuals who
measure the test colors nearly alike do not take the same correc-
tion. This is exhibited by the two red-sensitive observers of
Fig. 6. One evidently has a much narrower luminosity curve
than the other, for the correction is much less, and it is obvious
that a monochromatic luminosity "curve" would not respond to
the connecting scheme at all.
Before going on to the case of other color differences we may
point out that in cases where a definite type of color difference
is to be measured repeatedly a correction determined in this way
makes it possible for any member of a laboratory force to make
normal measurements. Thus a correction determined for the
difference between standard and high efficiency incandescent
lamps would work for all lamps of the same relative efficiencies
and, what is more, it may be expected to work for all smaller
differences of the same type, as those between lamps differing less
in efficiency.
V.— TEST OF THE CORRECTING SCHEME ON OTHER
COLOR DIFFERENCES.
While this development opens up a number of interesting possi-
bilities we have been interested in pushing the question still
farther. Will a correction determined from our test colors, be
correct for other types of color differences ? To obtain an answer
to this question we have tried our various observers with their
eye correctors on a commonly met color difference, namely, that
between the standard "4-watt" carbon lamp, and a type "C"
tungsten lamp at 0.65 w. p. c. We were specially fortunate in
securing the cooperation of one observer who was known to be
color-blind, and of one other, who from our previous work we
knew to be rather far from normal in the opposite direction to the
individual just mentioned. The first observer required a 300
per cent, concentration of the yellow correcting solution8, the
second a 150 per cent, concentration of the blue correcting solu-
8 Working backward from the transmission curve of the correction solution required,
we find that the luminosity curve of this observer is closely that of the totally color-blind,
as shown in Fig. I,
IVES AND KINGSBURY: COLOR VISION
269
tion, as against a maximum of 100 per cent, for any of our other
observers.
The results are shown graphically in Fig. 7. To the left are
the relative values of the two lamps, in arbitrary units, as meas-
ured by the nine observers without the correcting device. To the
right are shown the relative values as obtained by the corrected
eyes, the dashed line through the middle is the true relative value
of the lamps. It is seen at once that all the observers, color-
blind and normal, have been brought quite close together and
RATIOS WITH
P\ CORRECTED EYES.
—.RATIOS WITH
UNCORRECTED EYES
Fig. 7.— Results, with uine observers, of applying correction calculated
from test color measurements to the color difference of 4-w. p. c.
carbon lamp and 0.65-w. p. c. tungsten lamp.
every observer, without exception, has been brought nearer to
the true value. An extreme variation of 15 per cent, has been
reduced to five. Broadly, therefore, the corrections determined
from the color difference represented by the two test colors serves
for the new color difference.
Upon examination, however, it will be evident that while the
improvement with the more abnormal observers is striking, the
ones initially nearer normal have not all profited equally. We
have cases of under-correction and cases of over-correction. The
corrected points do not lie within 1 per cent, of each other as
they should if the correction were perfect. This is exactly what
2/0 TRANSACTIONS I. E. S. — PART I
we had anticipated from the preliminary study of the luminosity
curves. No average correction can be expected to fit the smaller
differences. We have decided from our work that if an observer
measures the test colors off by less than 5 per cent, that there is
no object in applying this correcting medium for general work,
for his deviation from normal in all probability consists in local
irregularities of the spectrum luminosity curve not to be over-
come by an average correction.
The correcting scheme does not, therefore, as we have worked
it out, obviate the necessity for selecting a group of individuals
for making general heterochromatic measurements, as it would
do were the correction exact for each individual. We can, how-
ever, modify our requirement for five or more observers whose
mean value of the test colors is naturally correct, into a require-
ment of five or more corrected observers.
SUMMARY.
A method for correcting the spectrum luminosity curve of an
abnormal or color-blind eye has been developed. By a practical
application of this method to the flicker photometer it is possible
to (1) equip any observer so that he will read correctly color
differences of a given type; (2) equip a color-blind observer so
that he will not only read correctly color differences of a given
type, but also measure other color differences no farther from
correct than a random observer of "normal" vision will do.
The account we have given here is concerned chiefly with the
experimental study of the eye correcting scheme. The means
developed, involving the use of liquids in glass tanks, are ex-
perimental laboratory means. We believe it to be possible to
reduce the results of the work to a more practical form for gen-
eral use by the use of special glasses. Such practical develop-
ment may be reported upon later.
bailey: headlights 271
INCANDESCENT HEADLIGHTS AND PROJECTORS.*
BY P. S. BAILEY.
Synopsis: This paper is intended to outline the commercial develop-
ment of incandescent headlights and projectors. It gives a brief descrip-
tion of the manufacture, application and operation of various types of
headlights.
The appearance of the gas-filled tungsten lamp with a focus-
type filament, in commercial form, has stimulated the design of
several devices for the projection of light from an incandescent
source. The field for apparatus of this description appears to be
very broad. Aside from its application to the stereopticon and
to street railway requirements, there is an active tendency among
the steam railroads to adopt the incandescent head-lamp. In
addition, there is apparently a considerable opportunity for the
incandescent projector in marine work, such as in the equipment
of tow-boats, launches, and other small craft, to enable the pilots
to locate buoys, landing places, etc. Then, too, there is display
lighting, involving the illumination of flags and decorations, public
buildings, signs and the advertisement of seashore resorts. And
lastly, in the case of war, for military and naval operations.
Searchlights are being employed in Europe in the present hostili-
ties, as an aid in the digging of trenches, picking up the wounded,
burying the dead, detecting aeroplanes, blinding a charging
enemy, and assisting in attack.
The high powered arc searchlights with the necessary engines,
motors and generators or storage batteries to operate them, are
extremely heavy and cumbersome. For this reason, the incan-
descent projector, operated from a portable gasoline electric set
would appear attractive and worthy of the consideration of mili-
tary representatives.
Problems concerning the lighting of thoroughfares and interiors
of practically all descriptions, require light sources of relatively
* A paper read at a meeting of the New England Section of the Illuminating Engi-
neering Society, November 10, 1914.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
272 TRANSACTIONS I. E. S. — PART I
large dimensions, as they tend to reduce intrinsic brilliancy and
glare and improve diffusion. But the effectiveness of an illumi-
nant when used with parabolic reflectors or lenses depends greatly
upon its concentration into small dimensions. In fact, the nearer
the illuminant approaches zero dimensions the nearer do the
resultant effects approximate the sharply outlined beams so impor-
tant in light projection.
Undoubtedly these conditions are better met by the crater of
the carbon arc than by any other form of illuminant, for high
power work, but the purpose of this paper is to call attention to
the demand for apparatus using a lower power concentrated light
source, which does not require expert adjustment, trimming and
other minor attention.
After testing different lenses, reflector lens combinations and
reflectors, I have come to the conclusion that for a general com-
mercial proposition, combining effectiveness of beam, low initial
cost, maintenance, etc., the polished parabolic reflector of metal
or silvered glass has many points of superiority.
A parabolic reflector is, of course, understood to be a concave
reflector having a specular surface, so designed that all sections
through the axis of the reflector are parabolas of identical focal
length. Such a reflector has the unique property of reflecting all
rays of light, emitted from the exact focal point and impinging
on its surface, along lines parallel to its axis. Since it is impos-
sible to obtain mechanically a perfect parabolic reflector and
since no true point source of light is available, the ideal parallel
beam is never realized. Thus, granting that all sources of light
have more or less definite dimensions, a distinct angular dis-
persion is caused. A ray of light proceeding from the light source
at the true focal point and impinging upon the reflector will be
reflected in a direction parallel with the axis. Another ray pro-
ceeding from a point in the light source forward of the focus
will be converged across the axis, while a ray emanating from a
point back of the focus will diverge. So it may be said that dis-
persed cones of light will be emitted from all points on the reflec-
tor surface, each cone having an angle equivalent to that which
the source subtends with reference to the particular points.
It follows, therefore, that the angle of dispersion will increase
BAILEY : HEADLIGHTS 273
with increased dimensions of the light source and decrease with
increased distance of the light source from the reflector, or in
other words, with increased focal length.1 Considering the
reflector from the light source a distance sufficiently great that it
becomes essentially a point, all the light cones may be considered
to merge into a single cone and the relation which exists for one
cone holds approximately for all. So in considering the effect of
a projector at a distance of two or three hundred times its diam-
eter, it can be said :
First, with a light source of given dimensions, everything else
being equal, a reflector having the greater focal length will give
the greater concentration of beam.
Second, for a reflector of a given focal length, the angle of
dispersion of reflected light will be approximately proportional
to the dimensions of the light source.
As the focal length is increased, the parabolic curve opens out
very rapidly so that in cases where the diameter is limited, a
reflector of long focal length will cover a smaller solid angle about
the light source. The focus-type lamp gives approximately the
same intensity in all directions, so that the light flux striking the
reflector, which avails in producing the beam is nearly propor-
tional to the solid angle covered by the reflector. Therefore,
for a given diameter of reflector, the shorter the focus the
greater the amount of light flux impinging upon the reflector and
redirected to the beam.
In the practical design of a projector, the reflector and lamp
are of first importance. The diameter of the reflector is usually
limited by the cost and the possibility of mechanically accurate
work, as well as by the space at the disposal of the user. For
example, in the case of application to the automobile, it is neces-
sary for the designer to consider proportion as well as efficiency ;
so that the diameter of the reflector, as well as the size of the
incandescent lamp, is limited. Thus a short-focus reflector is
essential in producing the most efficient beam, since it covers the
greater solid angle about the light source.
Electric railway requirements may be divided into three classes :
city, suburban and interurban. The first requires in most cases
1 G. H. Stickney, General Electric Review, Dec, 1912. F. Nerz, Searchlights ; Their
theory and Application, Franklin, Electric lighting.
2J4 TRANSACTIONS I. E. S. — PART I
simply a marker on the front end of the car, as the streets are
usually well illuminated from other sources. The second requires
sufficient illumination to enable the motorman to discern objects
on dimly lighted streets of the outlying districts. In the third
case powerful projected beams are necessary, since there is often
no light on the right of way and the speed of the cars is accele-
rated in many cases to sixty miles an hour, or over, and it is
imperative, therefore, that the motorman discern an object at a
sufficient distance to allow him to bring his car to a stop that
he may avoid striking it.
It is at present customary in practically all suburban and inter-
urban work to use a portable headlight, which may be carried
from one end of the car to the other. Thus, the size and weight
of the head lamp must be kept within reasonable limits.
Fig. i shows a type of incandescent headlight for suburban or
moderate speed interurban cars. Fig. 2 is a headlight for
interurban cars.
A word on the development of the spun parabola may be of
interest to those who are not familiar with the process. First,
a wooden or steel form is turned out on a lathe so that the out-
side surface conforms to the drawing of the inside surface of
the parabola which is about to be produced. Then a piece of
circular metal stock, of sufficient area to cover the form, is
selected and held centrally between the form and a disk chuck
on a lathe. The spinner then proceeds to cause the circular blank
and form to rotate and by the use of blunt nose spinning tools
proceeds to force and stretch the metal over the form. The
piece is then trimmed at the edge, skimmed inside and then sent
to the finishing room for plating and buffing. Metal parabolas
may be produced with dies, but the larger sizes are more success-
fully spun.
Glass parabolas are often pressed, while in a hot pliable con-
dition, into moulds and then accurately ground, polished and
silvered. Such reflectors are naturally truer than spun metal
ones. Other glass parabolas are blown into moulds and prove
sufficiently accurate for all practical purposes. The pressed,
ground and polished parabolas are naturally very expensive and
ZT4
Figs, i and 2. — Two types of incandescent headlights.
Fig. 3 (on left)— locomotive headlight; Fig. 4.— Dasher type headlight.
in-
jf^^^\
W
\
m.
Fig. 5 (on left)— Incandescent projector; Fig. 6.— locomotive headlight.
Fig. 7.— A locomotive headlight in place.
Pig. 8. — A special rear-end equipment.
BAILEY : HEADLIGHTS 2/5
their cost precludes their universal use in the larger sizes for
railways.
The shallow parabola n in. (27.9 cm.) in diameter, 4 in.
(10. 1 cm.) focus, in the suburban headlight referred to above, was
designed to permit the use of lamps having bulbs as large as
5 in. (12.7 cm.) in diameter operating between 80 and 125 volts,
with wattages of from 100 to 320. The filaments of these lamps
do not reach the degree of concentration of the low voltage high
current lamps. Thus the shallow parabola aids in preventing too
great dispersion, as wrell as permitting the use of the large sized
bulb.
The deeper parabolas 12 in. (30.48 cm.) diameter, 1^ in.
(3.49 cm.) focus, with which the suburban headlights are
equipped, permit the efficient use of the more concentrated fila-
ment focus-type lamps, operating at 6 volts and 105-125 volts at
wattages of 36, 72 and 108, and 23, 36, 46, 56, y2 and 94, respec-
tively, having bulbs as large as 2]/% in. (5.39 cm.) in diameter.
The silvered glass parabola is the more efficient as it has the
truer reflecting surface.
The rough usage to which this class of apparatus is subjected,
makes it imperative that the lamps and reflectors be encased as
strongly as possible. Struck-up steel cylinders are used, which
are formed from deep drawing steel in a die. There are no
seams, as this method provides a one-piece casing which is ex-
tremely rigid. The doors which contain the glass fronts are also
struck-up and punched hinges are used. The hanger straps and
supporting legs are punched and riveted to the casing.
Another and more powerful headlight (Fig. 3) having a rolled
steel casing supported on a cast iron base, with classification
number boxes is available. This has been designed for use on
electric locomotives but can be applied as well to steam locomo-
tives. Here a larger reflector (20 in. (50.8 cm.) diameter, 2^4
in. (6.98 cm.) focus) has been designed. It can be furnished in
either brass or copper, silver plated and buffed or in buffed
aluminum. Copper is generally used for steam road sen-ice as
the metal resists the action of the gases so prevalent about large
stations and roundhouses. It is easier to spin than brass, but
does not usually take on so good a finish as brass, as the metal in
276 TRANSACTIONS I. E. S. — PART I
sheet form seems of somewhat coarser grain. Aluminum retains
its polished surface, as a rule, a little longer than silver and is
to be preferred in some instances, although the coefficient of
reflection for silver plate is approximately 86 per cent, against
approximately 61 per cent for sheet aluminum.
It is quite important that electric and steam locomotives em-
ployed in hauling passenger and freight trains be equipped with
classification numbers as a means of identification for tower and
switch men. This has been taken care of by the employment of
number boxes riveted to the sides of the casing. Each box is
provided with an opal glass diffusing member and a hinged door
containing a stencil and clear glass. Both glasses are puttied into
their frames to keep out the water and the doors are made
water-tight where they fit the number boxes, being held tightly
by latches and wing nuts. Light from the incandescent lamp is
permitted to pass through slits in the reflector and is diffused by
the opal glass sharply defining the numbers cut in the black
stencil.
There is a growing demand for a headlight for city and sub-
urban use which will project a beam comparable with that of the
more powerful automobile headlights, as the usual dasher type
headlights are in many cases insufficient. Such a headlight
(Fig. 4) has been developed and apparently meets the conditions
very nicely. It has so far been constructed with a cast iron cas-
ing, but it can as well be furnished in cast aluminum. A cir-
cumferential flange for attachment to the car dasher projects
midway between front and back, so that the device can be set
into the dasher. The casing contains a deep glass parabolic
mirror approximately 8jHs in. (21.27 cm.) in diameter and a
reliable focusing mechanism, which, by the way, is somewhat
conspicuous by its absence in similar types on the market to-day.
Tests on this device have proven quite satisfactory. It could be
easily converted for automobile service by a redesign of the
casing.
Too much cannot be said about the necessity of accurately
focusing the lamps. A slight variation from the proper focal
point oftentimes causes an amazing reduction in apparent beam
candlepower. The better forms of focusing devices permit of
BAILEY : HEADLIGHTS 277
adjustment backward and forward along the axis of the reflec-
tor, as well as radially.
In such cases as the wattage of the lamps employed will per-
mit, it is desirable to exclude all free air from headlight casings,
as this prolongs the life of the surface of metal reflectors. This
is accomplished by means of felt gaskets applied between the
door and casing. In cases where the wattage of lamps is so high
as to reduce their normal rated life where enclosed, there is no
alternative but to ventilate them well.
Another problem is the use of suitable glass in the doors. The
glass must be of good quality, low absorption and, when high
wattage lamps are used, must be composed of two layers of sec-
tional glass, one section staggered with respect to the other, to
reduce the effects of unequal expansion and contraction, or of a
special single pane of very refractory glass to answer the con-
ditions. Oftentimes birds, blinded and dazed by the glare of the
headlight, have come to grief within the confines of the reflector
when the door glass perchance was not sufficiently strong to with-
stand the impact.
Fig. 5 shows a simple form of incandescent projector with
swivel and trunnion base. This device is equipped with a 20 in.
(50.8 cm.) silvered metal parabola with 2^4 m- (6.98 cm.) focus
and a special 1,500 mean horizontal candlepower focus-type
tungsten filament, which operates at approximately 30 volts, in
series with a variable resistance on no-volt direct current. It
will operate as well from a transformer or compensator from an
alternating current cicuit.
In general, I might say that for the highest speed interurban
direct current service the tungsten filament lamp so far has its
limitations and the present luminous arc head-lamp will without
doubt be used for this purpose for some time to come. The
reason for this is that in order to reduce the dimensions of the
tungsten filament sufficiently to put it on a competitive basis with
the arc, it is necessary to operate it at very low voltage and com-
paratively high current, so that operating from a 550-volt circuit
the total wattage becomes a prohibitive factor. Where alter-
nating current circuits are available a compensator may be intro-
duced so that in this case no obstacle presents itself. The same
278 TRANSACTIONS I. E. S. — PART I
is true with respect to storage batteries. Also on existing 25-cycle
alternating circuits, the incandescent headlight is a boon as the
fluctuations of any appreciable extent are not observable, while
in the electric arc they are plainly visible.
If it were possible to obtain the ideal case of parallel rays,
candlepower could not apply on account of the failure of the
inverse square law. But, practically, at distances where the
beam can be considered as a single cone of light it is apparent
that the section of the beam will vary proportionally in area with
the square of the distance from the reflector. This being granted
and ignoring the absorption of the atmosphere, intensities at
various distances will be inversely proportional to the square of
the distances. Thus, in working at long range, there appears to
be no reason why the intensity cannot be referred to as apparent
beam candlepower, since this defines it as compared with the
candlepower of the original light source, if the distance at which
the test is made is given.
Apparent beam candlepowers obtained with parabolic reflectors
are enormous as compared with the original light sources without
reflectors. The reason for this is that a large part of the flux
of light, instead of being radiated in all directions is condensed
into a relatively small angle and thus reaches a much higher
intensity. The ratio between the apparent beam candlepower
and the mean spherical candlepower of the light source is often
referred to as the multiplying factor. This depends upon the
diameter and focal length of the reflector, the dimensions of the
light source and the percentage reflection of the surface.
The multiplying factor of the 20 in. (50.8 cm.) diameter sil-
vered metal reflector with 2)4 in. (6.98 cm.) focus equipped with
a special 6- volt, 126.3-cp. concentric helix filament tungsten lamp
has been proven by actual test2 to be approximately 5.500.
Much discussion has arisen concerning what constitutes a
proper apparent beam candlepower for steam railroad service.
Certain states have statutes requiring 1,500 unreflected candle-
power. The special 1,500-candlepower focus-type tungsten lamp
previously referred to, when placed at the focal point of the
20 in. diameter parabola shown, will give an apparent beam
1 Test by I,. C. Porter, Harrison, N. J.
bailey: headlights
2/9
candlepower of approximately 1,100,000. Other states require
that an object the size of a man, in dark clothes be observed at
a distance of 800 ft. in front of the locomotive on a dark night.
The Report of the Committee on Locomotive Headlights issued
by the American Railway Master Mechanics Association calls
for a headlight having a maximum beam candlepower not greater
than 3,000, referred to the center of a reference plane, from
500 to 1,000 ft. (15.24 to 30.48 km.) ahead of the locomotive
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Fig. 9. — Curves obtained from a headlight equipped with a 6- volt,
36-watt focus-type tungsten headlight lamp.
and not greater than 2,800 at the same distances in front of the
locomotive, but taken at 20 ft. (6.09 m.) either side of the axis.
(Height of the headlight 9 ft. 7 in. (2.92 m.) above the rail.)
The 20 in. (50.8 cm.) diameter reflector previously referred to
in this article will accomplish these results when equipped with
a suitable tungsten lamp.
In due time it is to be hoped that a national law will be made
to regulate the intensities of headlight beams. Such a step will
serve towards a considerably greater uniformity in design than
is now possible.
Fig. 9 shows curves obtained from a headlight (Fig. 2)
6
28o TRANSACTIONS I. K. S. — PART 1
equipped with 6-volt, 36-watt focus-type tungsten headlight lamp.
The full line curve was taken with a clear glass door pane. The
dotted line curve was taken with an amber glass door pane.
Observation tests made at Lynn show no apparent reduction in
glare at the same measured apparent beam candlepower for the
amber glass screen over the clear.
Fig. 7 shows a Boston & Maine locomotive equipped with
turbo-generator headlight outfit. Capacity of set is 100 watts
and generator delivers 6 volts, 9 amperes to the lamp. The
headlight is here shown mounted on the smoke-box door of the
locomotive, while the turbine and generator are located on top
of the engine just ahead of the cab roof.
Fig. 8 shows an incandescent headlight applied to gasoline
electric cars. Approximately seventy-five of these headlights are
in service, using 35-volt, 1 10-watt focus-type tungsten lamps
operated in series with a resistance from a 65-volt direct current
car lighting generator and are giving very satisfactory service.
Thus it may be observed that considerable attention has been
given to the design, construction and operation of incandescent
headlights and projectors for practically all service requirements.
BAYNES: STREET LIGHTING IN CHICAGO 28l
STREET LIGHTING IN CHICAGO.*
BY PIERRE E. HAYNES.
Synopsis: This paper describes a few of the most interesting engi-
neering problems met with during the rehabilitation of the street lighting
system of the City of Chicago. The method of arc lamp selection is sug-
gested as a method of approximation which is generally acceptable to
arc lamp manufacturers, and still enables the purchaser to obtain the very
best value for his money. The subway illumination design is a distinct
refinement in outdoor lighting where comparatively high intensities are
desired on both horizontal and vertical surfaces with a minimum of glare.
The first attempt to illuminate the public streets of Chicago
was made in the year 1805. At that time the hunters and trappers
following an old pathway along what is now Archer Avenue
extended their operations down as far as 18th or 22nd Streets.
The trip was at that time quite difficult and in order to guide
the hunters back to the fort a pine knot was fastened to a tall
pole and lighted every night. This improvised lamp was set up
probably a little east of the south end of the present Rush Street
bridge.
Little or no attempt at street lighting was made until the
manufacture of coal gas was started in the year 1850. The
council proceedings subsequent to that time contain many orders
for the setting and operation of flat flame gas lamps. Many
lamps of this type remained in service up to two or three years
ago.
In the year 1887, 105 electric arc lamps were installed east of
the Chicago River from Kinzie to Polk Streets and since that
time the total number of such units in service has increased while
the number of gas lamps decreased.
The adequate illumination of the streets of Chicago requires
the use of electric arc lamps, tungsten incandescent lamps, ordi-
nary and ornamental gas lamps and incandescent gasoline lamps.
The use of electric arc lamps is confined as nearly as possible
to business streets, traffic streets, and unshaded residence dis-
* A paper read at a meeting of the Chicago Section of the Illuminating Engineering
Society, June 10, 1914.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
2&2 TRANSACTIONS I. E. S. — PART I
tricts or in districts where the density of population is not suffi-
ciently high to warrant the high initial cost of ornamental
tungsten lamp post construction. The total number of arc lamps
in service is about 19,000, of which 11,444 are 10-ampere alter-
nating current flame arc lamps. The remainder of the lamps in
service consist of direct current open and alternating current
enclosed arc lamps, there being about 1,000 of the former and
6,000 of the latter.
The keen quality competition of the American arc lamp manu-
facturers and the price competition of the foreign manufacturers
necessitated more exact methods of comparison than has hereto-
fore been used in the selection of such units. The American
manufacturers took ready advantage of many of the suggestions
made by the city's engineers and as a consequence changed some
points in their lamp design very materially.
SELECTION OF ARC LAMPS.
The proper selection of an arc lamp must take cognizance of
many points and in order that a proper grading may be given to
each type of lamp submitted, each of these points must be given
a weighting so that the grading given to each type will fairly
represent the value of that unit under the conditions for which
it is selected. Out of a total of 168 points allowed for a perfect
lamp, the various characteristics were graded as follow- :
Total light flux 10
Light distribution 10
Light constancy 10
Light efficiency 10
Mechanical efficiency .... 5
Regulation of voltage 5
Power factor 3
Accessibility of mechanism 20
Design 20
Materials 20
Reliability 30
Orbon consumption 25
Attention will be directed to the methods used in estimating only
two of the points listed above, the other methods being obvious
from the name assigned to the different characteristics.
In a large shop the matter of standardizing stocks of materials,
spare parts, and shop routine becomes extremely important if any
HAYNBS: STREET LIGHTING IN CHICAGO 283
efficiency is to be obtained, and an attempt was made in this case
to reduce the number of parts in a lamp to a minimum, to make
these parts accessible as they are assembled in the lamp, and to
reduce the number of special parts as far as was practicable. In
order to determine which of the competing lamps was best
according to this standard, accessibility or dissembly tests were
made. The various lamps submitted were taken to the city shop
and placed in the hands of any operator which the manufacturer
desired to furnish. This operator was required to dissemble and
assemble some eighteen or twenty parts characteristic to all lamps
competing. The number of smallest parts handled and the num-
ber of operations were recorded and the total for each lamp
taken inversely represented to a fair degree the relative value of
the lamp to its competitors. In every case the lamp showing the
best grade was given the maximum value shown on the table
previously given. It was interesting to note that three distinctly
different types of lamps did not vary more than 25 per cent, from
each other in accessibility by this method of test while the various
estimates based purely upon the judgment of experienced men
varied as much as 100 per cent.
In the matter of design, the grades were assigned after a very
careful consideration of the fundamental principles involved and
the manner and extent in which the manufacturer had adhered
to them. Attention is called to the fact that some serious depart-
ures from a theoretically perfect lamp were found.
The posts (Fig. 3) used for mounting flame arc lamps have
been approved by the Chicago Art Commission and are standard
in this city for this type of construction.
LIGHTING OF SUBWAYS.
In Chicago the steam railroads are elevated and at intersections
of these elevations with public streets there are found what are
termed "subways." These subways or viaducts were a source
of considerable danger on account of lack of illumination until
a short time ago. Where the elevation ordinances specifically
require it, the railroads have or are planning to illuminate these
subways according to specifications drawn by the commissioner
of gas and electricity. The remainder are now lighted by the
284 TRANSACTIONS I. E. S. PART I
city according to specifications considerably better than those
under which the railroads are required to work.
The railroads first proposed a method of installation of sub-
way illumination and one subway was wired according to this
method. Fig. 1 shows this subway at night time under the illum-
ination provided by the railroad method. The shadows and
glare spots are quite noticeable. The department of gas and
electricity then made an installation according to what seemed
to be the best and most practicable method. Fig. 2 shows the
result. Here it is plain that practically all shadows have been
eliminated. Subsequent tests showed that the illumination de-
rived from the railroad method was inadequate. The city
method provides more uniform illumination in the line of most
rapid travel, the vertical surfaces are adequately illuminated, and
the angle reflectors shade the eyes from the intense glare of the
lamps in the driveway.
Following the subway illumination work attention was turned
to grade crossing illumination. Fig. 7 shows a sheet used in the
department of gas and electricity by foremen in laying out sub-
way and grade crossing jobs. Over 4,000 25- watt tungsten
lamps are in use in the subways lighted by the city. Each lamp
serves approximately 400 sq. ft. (36.8 sq. m.) of subway area.
All lamps are installed in high grade porcelain steel reflectors.
Driveway lamps are installed in angle reflectors and are placed
over the curb and the horizontal axis of illumination turned 45
deg. toward the direction of traffic.
INCANDESCENT LAMP LIGHTING.
Electric. — The construction of the ornamental tungsten lamp
post lighting system (Fig. 4) made use of old gas lamp posts.
This installation consists of the old post with a top casting which
supports the globe and contains a series lamp socket with a film
cut out. The illumination obtained from this unit is of very
low intensity, quite uniform, and extremely pleasing. Moreover,
visual efficiency under the illumination provided is very high
considering the low foot-candle values found.
Gasoline. — The gasoline lamp has been used for many years for
the illumination of isolated locations where gas or electricity are
not available.
Fig. i. — Railroad subway lighting.
Fig. 2. — Railroad subway lighting.
H
it J 1
mm
fSmm
iff
fl his' ' "
ifl:.
TT- ^^33]
Ir^t
^^M
zzrf^JE
i
i
#
i
Fig. 3. — Flame arc lamp and
standard post.
Fig. 4.— Electric incandescent lamp post
with street sign attached.
i-u J. ornamental gas lighting
standard.
Fig. 6. —Standard post for commercial
lighting.
HAYNES: STREET LIGHTING IN CHICAGO
285
The amount of gasoline consumed is 65 grams per hour per
lamp and the candlepower obtained is in excess of 50 at the hor-
izontal.
~-fc-
SUBWAY LIGHTING
TYPE-A
TYPE-B
TYPEC
TYPED
3 COLUMN SUBWAY
2 COL. SUBWAY Z COL.NARROW SUB. OPEN SUBWAY
GRADE CROSSING LIGHTING
IARC ZINC.0R
EGAS
4GAS0LINE
0R4INC.
IARC 6INC.0RGASIFSPACE
BETWEEN TRACKS IS IN-
SUFFICIENT ARCS MUSTBE USED
Fig. 7. — Plan used in laying out subway lighting.
Gas. — Up until a very few years ago the city used an old type
of incandescent gas lamp which was capable of giving from 25
to 30 cp. on the average. This unit now yields in excess of 50 cp.
measured horizontally and uses less fuel than before.
CANDLEPOWER
Fig. 8.— Light distribution from 10-atnp. alternating
current flame arc lamp shown in Fig. i.
Fig. 9.— Light distribution
from tungsten lamp unit
shown in Fig. 2.
The increase in efficiency of street lighting in this city has
been remarkable during the last three years. Both the number
and efficiency of units have been increased while costs with the
exception of the cost of gasoline units have decreased. The cost
of operation of gasoline units has increased on account of the
286 TRANSACTIONS I. E. S. — PART I
change in market price of the fuel used. This cost is now so
high that the gasoline lamp is being replaced as rapidly as possible
by other and cheaper types.
The method used in checking the candlepower and continuity
of service of gas and gasoline lamps is worthy of mention.
Twenty-five per cent, of all gas and gasoline lamps in each class
of service are inspected each month during the lighted period.
The condition of all lamps inspected is considered as indicative
of the condition of all lamps of that class of service for the
whole month and a deduction is made from the contractor's bill
based on whatever percentage of lamps tested or inspected fall
within the limits of the following classes:
Candlepower
45 Excellent No reduction
35-45 Good 5%
25-35 Fair 20%
15-25 Bad 80%
Out 100% "
Photometric measurements are made from time to time, meas-
urements being taken of horizontal candlepower with all glass-
ware in place These tests are made on the street using a port-
able photometer in connection with a special adjustable stand
which is carried on a wagon. All tests are taken directly from
the wagon and it is unnecessary to climb out except to measure
the distance from the lamp to the photometer screen.
ORNAMENTAL LAMP POSTS.
A demand has arisen for an ornamental gas lamp. The use
of the present type of lamp with diffusing glass did not appear
to be the best thing obtainable. Single and upright mantle lamps
were tried in spherical globes and finally a vase shaped globe
was tried. The effect, using this globe, was very satisfactory,
the internal reflection of the globe making the single inverted
unit as efficient with diffusing glassware as it was in the old type
of lantern with clear glassware. Exhaustive tests of this type Of
globe (Fig. 5) showed that it increased the amount of downward
illumination with all mantle combinations, but that the maximum
increase of 23 per cent, was obtained using the single inverted
mantle. This unit will be used wherever it is desirable to have
an ornamental gas unit.
IIAVXES: STREET LIGHTING IN CHICAGO
287
Various special problems come up from time to time and
these are handled with the general idea that fixtures and opera-
tive methods are to be standard and that intensity must be uni-
form and brilliancy low.
CANDLEPOHER
3
0
0 0
O
c
>
>
> 0
00
0
0
4*11
r
\
1
T~~^~it~
1
jj "•
Q}f^
— r-1
<^S, ^*-^A*
'"^r^,
e
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/ 1
/
/ 1
rw ^«
<^5
5<6\
's\
c —
f
//
— -
^r^\
^
Fig. 10. — Light distribution from (1) single upright mantle with round
white glass globe; (2) single upright mantle with vase shaped
white glass globe; (3) single inverted mantle with round white
glass globe; (4) single inverted mantle with vase shaped white
glass globe; (5) double inverted mantle with round white glass
globe; (6) double inverted mantle with vase shaped white glass
globe.
The development of the new commercial lighting post (Fig. 4)
used principally by the Commonwealth Edison Company followed
out these ideas very strictly. The post itself was designed by the
Art Commission and the choice of lamps, lamp heights, and glass-
ware was prescribed by the city.
In the business districts this post must be 16 ft. (4.87 m.)
from the street level to the center of the suspended globes and
in outlying districts this dimension must be 12 ft. (3.65 m.).
The increase in efficiency was remarkable when the old height
of 10 ft. (3.04 m.) was compared with the newer heights of 12
and 16 ft. All the new cluster lighting upon Chicago streets must
be of this type (Fig. 6) at the end of five years.
DISCUSSION.
Mr. Hans Schaedlich : The lighting system of Chicago is
different from that of any other city in the world in that the
series circuits are fed in multiple from 250 kv-a. transformers.
_'SX TRANSACTIONS I. E. S. PART I
These transformers supply current for from six to fifteen circuits
at a potential of 5,050 volts. In order that a ground upon one
circuit may not react upon the operation of the other circuits
operating from the same transformer, one side of the transformer
must be grounded permanently. The transformers are connected
in banks of three, delta on the primary and star on the secondary
side, with the neutral grounded. This system of operation has
two special features, one is that the occurrence of a ground
causes a short circuit upon the line and the other is that on
underground circuits there is a considerable difference of current
between the phase and neutral ends of the circuit. The first of
these peculiarities is taken care of by the careful selection of the
current regulating device, and the second by the proper balancing
of the capacity and reactance of the lines.
The question of the gas-filled tungsten lamp standing up under
the shocks of operation due to grounds was satisfactorily settled
by repeatedly subjecting two of these units to the worst condition
possible. For this test the lamps were placed upon an experi-
mental circuit fully loaded and all the load with the exception of
these two lamps was suddenly short-circuited through an oil
switch. This test was repeated some twenty times and the lamps
withstood this treatment perfectly. The lamps are now burning
upon arc circuits. This test subjected the lamps to more excess
rushes of current than would occur during several years of actual
operation.
The size of the unit selected is the 300- watt 600-candlepower
20-ampere lamp. The lamp housing was designed by the city's
engineers, as the appearance of the units on the market were so
radically different from that of the flame arc units now in service
as to hamper the uniformity of the lighting system. Further-
more, the ventilation of the fixtures on the market was not suffi-
cient, in the opinion of the city's engineers, to properly dissipate
the heat generated by the lamp.
The 600-candlepower lamp is, due to the steadiness of its light
and due to lack (if depreciation of the volume of light (as during
a trim of an arc lamp) at periodic intervals, slightly superior to
the flaming arc lamp with its initial maximum eandlepower of
1.1 -1 through a diffusing outer globe.
TRANSACTIONS
OF THE
Illuminating Engineering Society
VOL. X JUNE lO. 1915 NO. 4
THE THEORY OF COLD LIGHT.*
BY WILDER D. BANCROFT.
Professor of Physical Chemistry, Cornell University.
Synopsis: It is claimed that all chemical reactions tend to emit light
and that they all emit light if made to take place very rapidly. It is
shown that the luminescence of salt flames is a chemiluminescence, and
the method of determining the reaction is outlined for the specific case
of cupric chloride. If a suitable chemical reaction can be made to take
place sufficiently rapidly, without any marked evolution of heat, cold
light is obtained. The firefly has solved this problem, though the nature
of the substance which oxidizq^ is not known. The chemist will some day
solve it in another way. The Moore light is probably a case of chemi-
luminescence ; but most commercial forms of lighting depend on tem-
perature radiation for their efficiencv.
When opaque substances such as carbon, platinum or earthen-
ware are heated sufficiently they emit light, the quality and inten-
sity of which depends on the temperature and not on the nature
of the substance heated. Radiation of this sort is called tempera-
ture radiation. An opaque gas would also emit light if heated
to a suitable temperature. Iodine vapor, for instance, glows1
when heated to above 5000 C. While this may not be entirely a
temperature radiation, it is usually so considered. The law of
temperature radiation holds only for opaque substances, which
are sometimes called perfect radiators. An absolutely trans-
parent substance would give no temperature radiation. At the
end of the eighteenth century Wedgwood2 showed that heated
air is not luminous. Subsequent experiments have confirmed this
conclusion of Wedgwood's.
Most artificial lighting is due to temperature radiation from
* A paper read at a meeting of the Pittsburgh Academy of Sciences and the Illuminat-
ing Engineering Society, December 10, 1914.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
1 Salet; Ann. Chim. Phys. (9) vol. 28, p. 34 ; 1873. Cf. Bancroft and Weiser; Jour. Phys.
Ch'm.. vol. 18, p. 295 ; 1914.
- Phil. Trans., vol. 82, p. 272; 1892. Cf. Bancroft and Weiser; Jour. Phys. Chem., vol 18
p 2"! ; 1914.
290 TRANSACTIONS I. E. S. — PART I
solid particles. In the kerosene lamp the light is due to glowing
particles of carbon. The difference between the kerosene lamp
and the gas jet is that the temperature of the latter is higher.
If all the solid particles are burned, as in the Bunsen burner, a
so-called non-luminous flame is obtained, even though the tem-
perature is much higher than in the burner with a luminous
flame. The brilliancy of the lime light is due to temperature
radiation from intensely heated lime. In the Welsbach mantle
and in the Xernst lamp there are suitable mixtures of rare earth
oxides instead of the calcium oxide used in the lime light. There
is some question whether the light from the Welsbach mantle is
exclusively due to temperature radiation, but it is unnecessary
to go into that matter now.
At first one would suppose that the incandescent lamp would
give the most efficient temperature radiation known because
graphite melts at a higher temperature than any other known
substance. The carbon lamp can be made to give an extraordi-
nary light efficiency, but its life is extremely short under these
conditions. The graphite vaporizes or disintegrates and the fila-
ment breaks.3 There has therefore been a systematic search for
substances with high melting points and low vapor pressures.
As a result, there have been produced successively the osmium,
the tantalum, and the tungsten lamps. In the nitrogen-filled
tungsten lamp the thermal radiation has been cut down and con-
sequently less power is needed to heat the filament to a given
temperature.
While it would be foolish to claim that the limit of efficiency
has been reached, it must be remembered that a large number of
very able men have been attacking this problem of temperature
radiation systematically and that consequently the limit of effi-
ciency is probably being approached. That brings up the question
whether light may not be produced in other ways than by tem-
perature radiation and, if so, whether it is possible to produce
cold light. The possibility of cold light cannot be disputed
because the firefly produces it. Langley's studies of the firefly
have shown that the insect gives about 95 per cent, efficiency,
meaning thereby that 95 per cent, of the radiations are in the
• Werner von Bolton obtained 0.3-watt per candlepcwer for a moment with r antalum
lamp.
BANCROFT: THF, THEORY OF COLD LIGHT 291
portion of the spectrum visible to the human eye while only
about 5 per cent, of the radiations are in the ultra-red portion of
the spectrum and what are popularly called heat rays. The light
of the firefly cannot be due to a temperature radiation because
the firefly does not burn up instantaneously. It is not a question
involving life because the abdominal portion of the firefly can
be dried, pulverized in a mortar, and kept for two years. At
the end of that time the powder will glow if moistened and
exposed to oxygen. It is simply an oxidation process. The fire-
fly has the power of secreting a substance which burns with a
luminous, cold flame. If one were to make in the laboratory the
unknown substance which the firefly makes, it would behave in
exactly the same way as the natural product. It would be
amusing to do this; but that is all that it would be, because the
product would be too expensive to use as a source of light.
Nobody claims for the firefly a low cost of production. In fact,
it is not known how one would estimate the firefly's cost of
production.
Under certain circumstances cold light can be produced in the
laboratory. Angstrom4 has calculated that he gets about 95 per
cent, light efficiency when he passes a current through nitrogen
under 0.1 mm. pressure. The losses at the electrodes and at the
walls of the tube cut the working efficiency down to about 8 per
cent. From this work of Angstrom's, it seems probable that the
Moore light is not a temperature radiation but is due to chemical
reactions.
Phosphorescing substances, such as zinc sulphide, emit light
at low temperatures and do not involve temperature radiations.
As yet, however, such substances as Balmain's paint, etc., have
to be exposed to light before they will emit light. Until some
other way of stimulating them is found, they are of more theo-
retical than practical importance. At present very little is known
about the chemical reactions involved, because these substances
have been studied chiefly by physicists.
The luminescence of salt flames are of great importance theo-
retically. By putting different salts into the non-luminous flame
of a Bunsen burner different colored flames are obtained : yellow
4 Wied. Ann., vol. 48, p. 493 ; 1893.
292 TRANSACTIONS I. E. S. — PART I
with sodium, pink with lithium or strontium, blue or green with
copper. Since the temperature of the flame is about the same in
all these cases and since one cannot very well claim selective
absorption in each case, it seems certain that the colors of these
flames are not due to temperature radiation and the problem is
to find out what does produce the luminescence.
One usually gets the same yellow color with different sodium
salts and one is consequently tempted to say that the yellow color
is due to the sodium atom when heated to a suitable temperature.
This is not true, however, because sodium salts emit little or no
yellow light in the hydrogen-chlorine flame, even though this is
fully as hot as the flame of the Bunsen burner. "' The next
assumption is that the yellow color is due in some way to sodium
metal and that the metal is present in one flame and not in the
other. The presence of free metal in the flame is not impossible.
Almost all salts are formed with evolution of heat and conse-
quently will dissociate if the temperature is high enough. It
therefore becomes a question of fact whether a given salt dis-
sociates in a given flame or not. To test this, use has been made
of a modification of Deville's hot-cold tube. Cold water was
run through a porcelain tube and the chilled porcelain tube was
held in the colored flame. With salts of copper, cadmium, tin,
silver, lead, bismuth, zinc, antimony, and arsenic in the Bunsen
flame, mirrors of the metals were obtained on the porcelain tube.0
With salts of mercury a grey deposit was obtained consisting
of drops of mercury. No experiments were made with gold or
with the platinum metals. No mirrors of tungsten or molyb-
denum could be obtained from oxides of these metals in the
Bunsen flame, but good mirrors were obtained with the hotter
oxyhydrogen flame. From the cooler portions of the oxyhydro-
gen flame tungsten blue and molybdenum blue were precipitated
on the tube. When sulphur dioxide was led into the hydrogen-
air flame, sulphur was precipitated on the porcelain tube. No
copper was obtained when copper salts were fed into the hydro-
gen-chlorine flame, showing that the amount of metallic copper
it in this flame is at any rate very much less than in the
Bunsen flame.
* Cf. Bancroft and Weiser; Jour P/iys Client., vol. J>). p. 310; 1915.
* Bancroft and Weiser ; J<>u> . I'hys. Chem., rol. 18, p. 261 ; 1914.
BANCROFT: THE THEORY OF COLD LIGHT 293
It is not to be expected that mirrors of metallic sodium and
potassium would be produced. There is, however, some evidence
that the metals are actually precipitated. The sodium chloride
is distinctly alkaline when precipitated from the hottest flames.
This is probably not due to hydrolysis in the heated gases, because
caustic soda is more volatile than sodium chloride and consequently
should be found in larger amounts in the outermost portions of
the flame. This is not the case, for the sodium chloride from the
outside of the flame is neutral. The greatest alkalinity is obtained
under the conditions under which one should expect to have the
largest amount of free metal. While this is not absolutely con-
clusive in itself, it is pretty satisfactory when taken in connection
with the behavior of the other metals.
It is evident that a number of reactions are taking place simul-
taneously in a flame colored with a salt. It is now believed that
all reactions tend to emit light7 and that they all emit light if
made to take place very rapidly, the critical reaction velocity
varying enormously in different cases. It is known that increas-
ing the rapidity of a reaction which emits light increases the
intensity of the light8 without producing much change in the
quality. While the vaporized salts are sometimes colored, as in
the case of cupric chloride, and may therefore give temperature
radiation to some extent, it is clear that most of the light emitted
by salt flames is due to chemical reactions and is to be classified
as chemiluminescence.
Some progress has been made in determining the reaction cor-
responding to a given color. The following results9 were obtained
for copper salts in the Bunsen flame:
I. Cuprous ion to cuprous salt = red.
II. Copper to cuprous ion = green.
III. Cuprous ion to cupric salt = blue.
The first conclusion is based on the action of cathode rays on
cuprous iodide, the third on the combustion of cuprous chloride in
chlorine, and the second on the combustion of copper in oxygen.
A number of experiments were made on the rapid reduction of
cupric and cuprous salts with sodium and aluminum as reducing
' Bancroft ; Jour. Franklin Inst., vol. 175, p. 129 ; 1913.
8 Trautz, Zeit. Eleklrockemie, vol. 10, p. 595; 1904. Zeit. Phys. Chem., vol. 53, p. 10S; 1905.
» Bancroft and Weiser; Jour. Phys. Client., vol. 18, p. 323; Trans. Am. EUctrochem .
Soc. vol. 25, p. 123 ; 1914.
294 TRANSACTIONS I. E. S. — PART I
agents. No characteristic luminescence could be obtained, pre-
sumably because these reverse reactions were not made to go
sufficiently rapidly. However that may be, it is clear that reduc-
tions play no important part as regards the light emitted by
copper salts in the Bunsen flame.
When a solution of cupric chloride in aqueous hydrochloric acid
is sprayed into the Bunsen flame, there is a red or violet tip to
the flame and when the flame is burning steadily one can often
see a violet sheath around the flame. This is not a true lumines-
cence, though it looks like one. It is merely the color of cupric
chloride vapor. It can be obtained in mass by heating copper in
an electric furnace and then running in chlorine or by volatilizing
cupric chloride.
When cupric chloride is sprayed into a hydrogen-chlorine flame
or when a mixture of cupric chloride and hydrochloric acid is
sprayed into a Bunsen flame, the hydrochloric acid cuts down
the dissociation of the cupric chloride and there is a reaction from
cuprous ion to cupric salt but not the reaction from copper to
cuprous ion. Consequently the flame is blue and not green. The
same result ought to be obtained without the acid if one used a
flame the temperature of which was not sufficient to dissociate
cupric chloride into free metal and chlorine. The alcohol flame is
just on the dividing line. Cupric chloride colors a hot alcohol
flame green and a cooled alcohol flame blue.
Since the yellow of the sodium flame is due to the reaction
from sodium to sodium ion, the hydrochloric acid from a hydro-
gen-chlorine flame will force back the dissociation and cause the
yellow to disappear practically completely.10
Since the bulk of the light in salt flames is due to chemical
reactions and not to temperature radiation, there is a possibility
of duplicating the effect, if one can cause the reactions to take
place sufficiently rapidly at low temperatures; in other words, if
they are done electrolytically. Some years ago Schluederberg11
showed, in the Cornell laboratory, that light is emitted when an
alternating current is passed through lead electrodes in sulphuric
acid. Later, Wilkinson1- obtained flashes of light with a number
'« Bancroft and Weiier ; Jour. Phys. Client., vol. 19, p. 310 ; 11,15.
>• Jour. Phys. Chrm., vol. 12, p. 623 ; 1908.
>- /old., vol. 13, p. 695; 1909.
BANCROFT: THE THEORY OF COLD LIGHT 295
of metals as anodes, using a direct current. Owing to film
formation, the light could only be seen for an instant. By press-
ing a tooth brush against a rotating anode, it is possible to
remove the film as it gets too thick and thus to obtain light con-
tinuously for an indefinite period, ten minutes for instance. So
far we have not been able to obtain an electrolytic flame with
copper which could be shown to a large audience, but we can do
this readily with mercury.13
When mercurous bromide or mercury is burned in bromine an
orange light is emitted. When mercurous or mercuric bromide is
exposed to the cathode rays a similar orange light is obtained.
When mercury is made anode in a cold, fairly concentrated,
potassium bromide solution (25 per cent., for instance) with an
anode current density of about 2 amperes per square decimeter,
the mercury first becomes coated with a film of bromide and
then appears to glow with a brilliant orange light. This will
last for at least ten minutes, at the end of which time the film
of bromide will have become so thick as to prevent the light
being seen. By looking carefully from the side, light can still
be seen between the film and the surface of the mercury. The
light can be obtained at as low a voltage as 3 volts, but the
intensity is then very low. With increasing voltage — or really
with increasing current density — the intensity of the light in-
creases, the upper limit coming when visible sparking takes place.
The phenomenon is shown very well with a voltage of 24-28 volts.
This is not cold light. It is not even a very efficient light. The
importance of it lies in the fact that it is a striking illustration
of the principle that reactions emit light and that a high tempera-
ture is not essential. To obtain cold light one must find a reac-
tion which can be made to go rapidly, which absorbs heat or
evolves but a small amount of heat, and which has a high con-
version factor for light. A number of other requirements come
in. if it be stipulated that the light shall be suitable for commer-
cial purposes. There is no immediate prospect of the present
methods of lighting being superseded; but the theoretical feasi-
bility of cold light and the general conditions under which it is to
be obtained have been demonstrated.
is Bancroft and Weiser ; Jour. Phys. Chem., vol. 18, p. 762 ; 1914.
296 TRANSACTIONS I. E. S. — PART I
PIPINCx HOUSES FOR GAS LIGHTING.*
BY II. R. STERRETT.
Synopsis: This paper emphasizes the importance of having a specifi-
cation which will thoroughly cover the installation of all interior gas
piping. The method of handling this phase of the distribution system in
one city is described. The desirability of illuminating engineers deciding
on the location of outlets is also discussed.
Although the Illuminating Engineering Society has primarily
to do with the utilization of energy in the form of light, the de-
sign of burners and reflectors, the study of the effect of light
upon the human eye, the determining of the quality and proper
amount of illumination for the great number and variety of con-
ditions under which artificial light is necessarily used, it is the
object of this paper to tell something of the means used to convey
that form of light energy commonly known as illuminating gas to
the various outlets or points where it is to be converted by com-
bustion into light or heat.
Broadly speaking, any distribution system may be divided into
four component parts; mains, sen-ices, meters and house piping,
each of which contributes equally to the satisfactory supply of
gas. Of these divisions the first three are under the gas com-
pany's control, and hence, are usually properly installed and
maintained.
A brief description of a typical low pressure distribution sys-
tem might now be apropos.
From the works where the gas is made there is a net work
of trunk or principal mains, which act as feeders for the thous-
ands of branch pipes which supply gas to all parts of the city.
In a large plant gas as manufactured is forced through pusher
mains usually of 20 in. or 30 in. pipe ( go.8 or 76.2 cm.) pipe,
• A pnper rod at a meeting of the Philadelphia Section of the Illuminating Engi-
neering Society. March ai, 1915.
The Illuminating Kngineering Society is not responsible for the statements or
opinions advanced by contributors.
STERRETT: PIPING HOUSES FOR GAS LIGHTING 297
under a pressure of from 10 to 70 in. (0.25 to 1.78 m.) water
column, the latter being a little less than 3 pounds (1.36 kg.)
per square inch (6.45 sq. cm.), to the various holders or re-
serve tanks.
The pusher mains are so interconnected that, if, for any reason,
something unforeseen should happen to either of the manufac-
turing plants, the other could instantly take up the additional
load without endangering the continuity of supply. During the
periods of low demand the holders are filled, and when the peak
load conies on the gas supply is ample. The gas is discharged
from the holder through governing valves into the distribution
system, which is under a pressure averaging about 3 inches of
water column. The distribution mains, which range from 6 to
48 in. in diameter, are so cross connected and interconnected
that any break in the system affects but a few consumers. Con-
tinuously recording pressure gauges are set in different parts of
the city so that any change in the gas pressure, due to increased
or diminished consumption, perhaps caused by a shifting pop-
ulation, can be adjusted by partly closing or opening the holder
valve. In this way the general pressure conditions are kept con-
stant within certain limits.
The remaining division of the distribution system, house
piping, is usually installed by plumbers or gas fitters, and does
not come under the direct control of the gas company. It is,
therefore, necessary that this work be properly inspected.
The importance of a specification which will thoroughly cover
the installation of all interior gas piping, cannot be too greatly
emphasized. In order that such a specification be of any real
value, it is very necessary that proper laws be enacted to insure
to the gas company the enforcement of the various rules em-
bodied in the specification.
In one large city, before any gas piping may be installed in a
building, it is necessary to obtain a permit from the bureau of
buildings, which also inspects the work when completed and
issues an approval card before a meter may be set. In another
city all piping must be installed in accordance with specifications
issued by the gas company, whose inspectors supervise the work ;
while in still another city all gas fitters must be licensed and file a
TRANSACTION'S I. IC. S. — PART I
plan of the proposed piping with the building department fur
its approval, the gas company supervising the installation.
In one city where about 375,000 meters are in use, the city
government by ordinance requires the gas company to exercise a
supervision over the character of material used and work done
in installing gas piping and fixtures. In accordance with the ob-
ligation thus created, the company has adopted a specification
for fuel and illuminating piping and fixtures. This specification
includes the kind of material, methods, locations, etc., to be used
and avoided in making installations, a schedule of pipe sizes and
lengths for various consumptions, instruction how to properly
draft a piping plan, and an explanation of just what is required
in the way of inspections by the gas company's representatives.
The piping schedule is based on Prof. Pole's well known for-
mula for the flow of gas through pipes,
n _ r K'(P, - p,)
where Q = cubic feet per hour ; d = diameter pipe in inches
Px = initial pressure, inches water; P_. = terminal pressure,
inches water ; L = length in yards ; \V = specific gravity of gas
(air = 1); C = constant.
A computer designed by Wm. Cox is based on this formula.
and saves much time which otherwise would be spent in making
calculations. With the computer, either the discharge, the re
quired size pipe, or the difference in pressure can be determined,
provided the other two are known.
If the sizes specified in the schedule are checked with the for-
mula they will be found somewhat in excess of the figures de-
rived from the latter, it being the desire of the gas company to
make provision for the future installation of additional ap-
pliances without necessitating an increase in the size of piping.
The smallest diameter pipe, and therefore the smallest outlet
permitted, is }$ in. (9.52 mm.), and this, it is assumed, will
usually supply i<> cu. ft. (0.28 cu. m.) per hour at the average
ire. The capacity of a larger outlet as compared with a
\s-in. outlet, varies directly as the areas. In designing a system
of piping, after the sizes of the various outlets and the best di-
rection to run the pipes have been determined, it remains to de-
STERRETT: PIPING HOUSES FOR CAS LIGHTING 299
cide the proper size piping to install. This is accomplished by
starting at that part of the system farthest from the meter and
working toward the latter, determining the proper sizes by con-
sulting the piping schedule. When the first branch line is reached
the sizes are again determined by starting at the far end of the
branch and proceeding to the junction, where the quantities of
gas for the two pipes are added and the same process repeated
until finally the meter is reached.
In drawing a piping plan, vertical lines show vertical piping,
horizontal lines show horizontal piping running the length of the
building, while the slanting lines show horizontal piping running
the width of the building.
When no outlets are open the pressure in a system of house
piping is uniform, except the small difference due to elevation,
each 10 ft. (2.54 m.) being equal to about V10 in. (2.5 mm.)
water column. Just as soon as a burner is lighted, gas begins to
flow through the piping and, as a result of frictional losses, the
pressure by the time the gas reaches the burner is reduced. Since
it is necessary to have a certain volume of gas at a burner, and
since the volume depends on the pressure as well as on the size
of piping, a certain pressure loss through a system of piping must
be used as a basic, so that in the piping schedule mentioned before
a loss of 2/io-in. water pressure between the meter and the farth
est outlet is considered as maximum. Then since there is from
2Vio_ to 35/10-in. (63.5 to 90. mm.) pressure on the mains and
services, the pressure at an appliance connected to the extreme
outlet would be from 2%0 or 3%0 in., there being about a 3/10-in.
drop through the meter.
Due to the fact that there is a certain unavoidable range in
pressure over an area as great as that included by the limits of
a large city, gas appliances are usually equipped with the neces-
sary means of adjusting the burner to take care of the different
pressures.
In one large city where the gas company is responsible to the
city government for all material and workmanship in the installa-
tion of house piping three inspections of interior piping are made,
the inspectors being employees of the gas company, impartial and
working for the combined interest of the consumer and the com-
300 TRANSACTIONS I. E. S. — PART I
pany. When an installation is ready for the first inspection, which
is made while the piping is still exposed, a plan of the system or
extension, plotted on a regular form, is forwarded to the gas
company. The inspector compares the actual installation with
the plan, and tests the piping for leaks, a pressure of 3 pounds
(1.36 kg.) per square inch (6.45 sq. cm.) as indicated by a
6-in. (15.24 cm.) mercury column, being applied for 10 minutes.
If the rules have been complied with, and the system is tight,
a certificate of first inspection is issued and the piping may be
covered. If any changes are necessary, they must be made be-
fore the certificate is granted. After all carpenter and other
building work, that might disturb the piping, has been finished,
and after the last coat of white plaster is on, the gas fitter
applies for the second inspection, which is principally one of
pressure and is made before any fixtures are hung. A pressure
test identical with that of the first inspection, is made, and if the
piping is tight a certificate of second inspection is given. After
the fixtures are installed and the system is ready to receive gas,
the third inspection is applied for. This, the last inspection, is
principally one of fixtures ; the entire system is put under a
pressure of 6-in. water column, which must show no drop in 10
minutes. Fixtures are examined for poor workmanship, ob-
jectionable design, etc., and all gas fixture cocks are carefully
measured with a special gauge made for the purpose of deter-
mining whether they comply with the fixture cock specification.
There is very little to say about the actual physical house
piping. It is simply a case of determining the proper location
of, and the approximate consumption of gas for, each outlet,
joining the various outlets to the riser, care being exercised so
that the piping is of the correct size, properly supported, sloping
in the right direction, etc.
In ordinary dwelling houses, which form the great majority of
cases, a system of house piping usually consists of a riser or pipe
running vertically from a point in the basement near the meter,
and supplying gas at each floor to a branch pipe, to which are
connected the various outlets on that floor. In larger dwellings
two or more risers may be run, all being supplied by one meter;
while in the case of apartment houses a separate riser and meter
STERRETT: PIPING HOUSES FOR GAS LIGHTING 301
supplies each apartment. The meters are always installed in the
basement, and in some cases where the number warrants, a special
meter room is built. In modern manufacturing buildings it is
the custom to install a trunk or common riser, the meter or meters
being set on each floor, according to the number of tenants
occupying it.
In most cases horizontal gas piping is run parallel with, and
under, the floor boards, which not only makes it more convenient
if the piping should ever, for any reason, need to be uncovered,
but also assures that it will be supported by the joists which may
be notched out as near their points of support as is possible.
Vertical pipes are usually run in hollow partition walls. When-
ever possible it is preferable to have the gas piping exposed to
view.
Piping may be laid level, but if not it should be sloped toward
an outlet where it can be properly dripped, that is, where any
condensation formed might be conveniently drained off.
After a system of piping has been properly installed, it needs
very little attention under normal conditions. In time a certain
amount of scale may form, and if this collects at any point the
area will be reduced and the pressure lowered, thus causing a
complaint from the consumer that the supply has been insuf-
ficient. By shutting off the gas at the meter and forcing air
through the pipes by means of a hand-pump, these obstructions
can usually be removed. The decision as to where each outlet
should be placed to afford the proper distribution of light, should
be made by an illuminating engineer. Of course, there are in-
numerable little houses where the small rooms, usually square
or oblong, do not allow fixtures other than central pendants or
side wall brackets to be installed, and in these cases it is of little
importance that the various outlets are located by one who, per-
haps, knows little or nothing about lumens, foot-candles, glare,
coefficients of reflection, etc. On the other hand, there are
thousands of larger residences, apartment houses, commercial
buildings, and school houses, where the size of the rooms does
not limit the type or location of lighting fixtures. In structures
such as these, the location of the light sources should rest with
one who is familiar with the principles of illumination.
302 TRANSACTIONS I. E. S. — PART I
The writer's attention was recently called to an instance where,
in an operation of the better class of dwellings, the living room
was very poorly illuminated, due to the improper location of the
outlet. By placing the fixture a few feet to one side, the lighting
could have been greatly improved. This is a case where good
illumination was evidently sacrificed in order to do away with
running the extra pipe extension.
In piping houses for gas, the outlets should be properly located
and the piping run to the outlets, instead of, as is the rule in so
many cases, locating the outlets according to the easiest and
least costly system of piping. If the members of the Illuminating
Engineering Society when the opportunity presents itself, will
emphasize this point, better illumination will result in many in-
stances.
The cost of installing a complete, modern system of gas piping,
if put in at the time the building is erected, varies from about
one-eighth of I per cent, to I per cent, of the total cost of
the building. These figures are based on the analysis of a large
number of cases, ranging from an ordinary residence to large
office and commercial buildings.
CRAVATH : THE LIGHTING OF SMALL INTERIORS 303
KXOWNS AND UNKNOWNS IN THE LIGHTING OF
SMALL INTERIORS.*
BY J. R. CRAVATH.
Synopsis: This paper attempts to summarize briefly the principal
known facts to be observed in planning the lighting of small interiors.
Some of the points in controversy and undetermined are stated and the
author's views are given as to a safe course to pursue pending the
acquisition of more definite knowledge on these points.
In attempting to summarize in this paper some of the principal
known and established facts in the illumination of small rooms
I can necessarily present but one point of view, my own, because
no two workers in the field would be likely to agree as to just
what can be considered "known" what "questionable" and what
"unknown." In my presentation of this matter I shall endeavor
to take what appears to me a rather conservative attitude. In
doing so I shall doubtless incur the criticism of some for having
gone too far and that of others for not having gone far enough.
Much that will be said here concerning the lighting of small
interiors applies equally to all classes of interior lighting.
Lighting of small interiors affects the comfort, convenience
and pleasure of far more people than any other class of lighting.
This subject will be taken up under three headings as fol-
lows :
(1) Comfort, efficiency and safety of the eyes.
(2) Physical efficiency in the utilization of the light gen-
erated.
(3) Esthetic or artistic effects.
Of these three the first relating to comfort and efficiency of
the eyes is by all means first in order of importance. As to the
others, whether efficiency in light utilization or artistic effect is
the most important depends altogether on the purpose for which
the small room is used. For the benefit of those who might say
that psychology should be introduced somewhere in my general
* A paper read at a meeting of the Chicago Section of the Illuminating Engineering
Society, April 22, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
304 TRANSACTIONS I. E. S. PART I
classification, it may be pointed out that psychology undoubtedly
enters both into questions of comfort and efficiency of the eyes
and into esthetic effects.
COMFORT AND EFFICIENCY OF THE EYE.
As a broad principle the comfort and efficiency of the eye de-
pends upon the distribution of brightness within the range of
vision.1'2-18 It should be kept constantly in mind that what-
ever is said in this paper regarding brightness values which are
good or bad for the eye assumes that the brightness under con-
sideration is actually within the range of vision. The eye is con-
cerned only with what it sees. Consequently if bright light
sources are not within the range of vision they are out of con-
sideration except for the reflection from them which may come
from glossy surfaces which are within the range of vision.
What is said here as to the known effects of light upon the eye
under a given set of conditions does not necessarily apply to all
individuals because there is fully as much difference between
what different eyes will stand as there is between the physical
strength and endurance of different persons. What is said here
is intended as applying to most of the people most of the time.
In the discussion of brightness values in this paper figures will
be given both in candlepower per square inch and in "apparent
foot-candles." An apparent foot-candle of brightness will be
here used as meaning a brightness equivalent to that of a perfect
mat diffusing and reflecting surface illuminated to an intensity
of 1 foot-candle. It is 452 times the candlepower per square inch.
While this is not yet a generally accepted method of expression
I believe it is valuable in conveying a more definite mental picture
than an expression in candlepower per unit area to those of us
who are constantly dealing with illumination as measured in
foot-candles.
Taking certain well known natural conditions as a starting
point, it is known that a clear blue sky having a brightness of
about 2 candlepower per square inch, or 904 apparent foot-
candles, can be faced with entire comfort when it fills the upper
part of our field of vision outdoors in the open or near a window,
provided the lower part of our field of vision consists of green
or gray fields or some equally dark surface. It is only when the
CRAVATH: THE LIGHTING OF SMALL INTERIORS 305
lower part of our visual field is filled with light reflected from
snow or desert or light colored roadway that a normal person
will experience discomfort facing a blue sky. However, if one
faces a small patch of this same blue sky and from the rear of a
small narrow office so that it stands as a bright patch amid dark
surroundings, it may be put down as a known fact that the
majority of people will experience discomfort within an hour or
two if not sooner.
The second known fact in connection with the comfort of the
eye and brightness of surfaces is that, even though a given sur-
face may be comfortable to face continuously under bright sur-
roundings, a surface of the same brightness if presented so as
to be in sharp contrast with its surroundings (that is very much
brighter than its surroundings) may cause decided discomfort if
continually within the field of vision for some time.
In the artificial lighting of small rooms it is well known from
the personal experience of many observant people that the ex-
posure of certain undiffused light sources, if of sufficient candle-
power, to adequately light the room according to modern ideas
will cause discomfort to the eyes. This is assuming, as said
before, that those bright sources are exposed to the eye for some
considerable period.
Beginning at the top of the list the brightest source of artificial
light with which one commonly deals in the lighting of small inte-
riors is the tungsten lamp with a brightness of over 1,060 candle-
power per square inch, or about 479>ooo apparent foot-candles,
or more. The gas-filled lamp is probably 2.500 to 3.000 or more
candlepower per square inch, or 1,130,000 to 1.350,000 apparent
foot-candles. As to the bad effect of exposed lamps of such
brilliancy in small rooms where persons must face them con-
tinuously there is practical agreement among illuminating engi-
neers and oculists, although it is by no means known or agreed
just what is the real cause of the discomfort or fatigue which is
commonly experienced.
Coming down from tungsten lamps to sources of less intrinsic
tightness there is the carbon lamp which is still uncomfortably
bright, namely, from 400 to 600 candlepower per square inch,
corresponding to 180,000 to 270,000 apparent foot-candles.
306 TRANSACTIONS I. E. S. — PART I
The Welsbach mantle of about 31 candlepower per square
inch, or 14,000 apparent foot-candles, may also be included
among the uncomfortably bright sources without much question.
Next comes a class of bright surfaces or light sources about
which there has been some controversy. These are the light
sources just enumerated when enclosed in diffusing glass.
A frosted tungsten lamp bulb has a brightness of 2 to 8 candle-
power per square inch, or 900 to 3,600 apparent foot-candles.
In this case there is an approach to brightness values comparable
with the sky in its various aspects. However, I have already
shown that sky brightness amid comparatively dark surroundings
can be uncomfortable, and in this case the surroundings in an
artificially lighted room are very dark compared with the frosted
tungsten lamp.1
The evidence seems to be steadily accumulating against the
use of exposed sources of this order of brightness where they
must be faced continuously. To the personal experience of the
many who find it unpleasant to sit and face such sources there
have been added the investigations of Dr. C. E. Ferree of Bryn
Mawr College who, by the use of his method of testing for eye
fatigue,3' 4, 5 has been able to reduce to a quantitative basis
some observations which heretofore could be made only in a
somewhat haphazard fashion. While it is true that the work of
Dr. Ferree's test so far has been confined largely to his own
laboratory supplemented by some confirmatory work6 done by
myself in 1914, I personally believe that as a result of these rather
extensive experiments it may be put down as one of the knowns
that, in the lighting of small rooms where the exposed sources
are such as to have a brightness of over 1 candlepower per square
inch or 452 apparent foot-candles, trouble from eye fatigue and
discomfort will follow from continuous work with the light from
such concentrated sources shining in the eyes.
Below 1 candlepower per square inch or 452 apparent foot-
candles brightness for the exposed light sources one enters a
region of uncertainty and controversy as to the effects on the
eye. The heavy pressed bowls used for semi-direct lighting at
the present time as actually used in the lighting of small interiors
generally have a brightness from about 2 candlepower per square
CRAVATH : THE LIGHTING OF SMALL INTERIORS 307
inch, or 904 apparent foot-candles, down to about 0.075 candle-
power per square inch, or 34 apparent foot-candles. With pure
indirect lighting the brightness of the ceiling (which is the visible
source of light) usually falls between 50 and 4 apparent foot-
candles in small rooms.
The researches of Dr. Ferree3 seem to indicate that there is
some eye fatigue when facing units of 0.71 candlepower per
square inch, or 320 apparent foot-candles in a room with light
colored walls. Extensive tests which I made last year6 indicated
no more fatigue with the subjects facing a brightness of 0.35
candlepower per square inch, corresponding to 156 apparent
foot-candles, in the shape of certain semi-direct lighting bowls
than was experienced with a pure indirect system. It is of course
obvious that the pure indirect system offers the minimum of
surface brightness with which it is possible to accomplish arti-
ficial illumination at the present time. As far as present informa-
tion goes from the tests cited and from experience it seems prob-
able to me that a brightness of about 0.5 candlepower per square
inch, or 230 apparent foot-candles, for semi-direct or luminous
bowl indirect lighting equipment for small rooms should be
about the maximum limit. Some semi-direct bowls at the present
time offer considerably greater brightness than this to the eye,
while others fall well under the limit.7
What has just been said applies to semi-direct and luminous
bowl fixtures of the sizes commonly necessary to light a room. If
the bright area exposed is small, however, so that the total candle-
power is low the limits just suggested may be comfortably ex-
ceeded.
So far in considering this subject of the effect of the brightness
of the exposed light sources upon the eye in small interiors only
the effect of the light which goes directly from the sources to the
eye has been considered. However, there is another class of
effects closely allied to the first, namely, the reflection from
smooth or polished surfaces, one example of which is commonly
known as "glare from paper." One of the thoroughly known
facts is the annoyance and eye-straining effects of this glare
from paper, polished tables, and all smooth polished surfaces.
This glare is simply the result of reflection from the original
308 TRANSACTIONS I. E. S. PART I
light sources. It is obvious that whatever is done to diffuse the
light from such sources — that is, to enlarge the area from which
the light comes — and reduce the brightness will be beneficial in
reducing the glare from paper. The same things that are bene-
ficial in diffusing the light from exposed surfaces for the comfort
of the eye are beneficial in reducing this glare from paper.
In some cases as with a shaded reading or desk lamp the source
of light is shaded from the eyes of the occupants of the room, but
is not shaded from the papers which are being read. In such
cases the position of the lamp with reference to the paper and the
eye is all important as the eye should not be in a position to
receive glare from the page. The correct position may or may
not be easy to attain.
It may be taken as fully known and demonstrated that diffused
light is best for reading and working on papers and polished sur-
faces. Much of the pleasing quality of daylight for reading is
due to its diffuse character. For sewing on cloth where the
direction of the light is such that shadows do not interfere,
direct light is equally satisfactory.
The result of hundreds of tests on many individuals 9- IQ. Ir on
the amount of light preferred for reading shows that the majority
asked for a lower intensity with diffuse than with direct or more
uni-directional lighting. In my opinion, considering the method
of making these tests, these results should be interpreted as mean-
ing that the diffuse lighting is more satisfactory rather than as
indicating that one can with safety plan for less illumination with
diffused or indirect systems. When the quality of illumination
is not satisfactory most people ask for more quantity regardless
of the real trouble.
It is established beyond controversy that a purely localized
illumination is not satisfactory.8- I9 The eye has not been evolved
under conditions such as prevail with a bright area in the center
of the visual field with the surroundings dark. This is the con-
dition that one finds with purely localized light such as is fur-
nished with an opaque shade concentrating light on some spot
upon which we are working with the eye; the rest of the room
being in darkness.
If we cannot get all our light for working purposes from
cravath: the lighting of small interiors 309
diffusing sources such as day skylight and indirect artificial light
we should at least provide as large a portion of the total light in
the shape of general diffuse light as possible. If necessary for
reasons of economy this can then be supplemented by such amount
of localized light as is necessary for the particular purpose in
hand. The presence of a considerable amount of general light-
ing, especially if it is well diffused, greatly enhances the comfort
with which work can be done under the localized light.
In the lighting of small offices, daylight coming through win-
dows usually has one important advantage over diffused arti-
ficial light coming from a ceiling, namely, the direction of the
light. Even with the best diffused indirect artificial light or
natural skylight from windows there is some trouble from specu-
lar reflection or glare from paper. It is easier to avoid this
specular reflection when the light is coming from one side as it
does from a window than when it comes from above. In a large
interior these difficulties largely disappear because of the large
expanse of lighted ceiling which increases the diffuse character
of the light received upon a page.
Those who would put unshaded bracket or table lamps almost
in the line of vision in a small room should remember that it has
been well demonstrated in connection with experiments on street
lighting both by Mr. A. J. Sweet12' '3 and by Mr. Preston S.
Millar14 that, when a lamp is brought within a range of about
25 degrees of the object which one is looking at, it has a blind-
ing effect which necessitates more illumination on the object in
order to see it with equal clearness. This effect increases as the
light is brought nearer to the line of the center of vision.
When the edge of a lamp shade is below the level of the eye
all that is necessary to guard the eye from the direct light of the
filament is to have the source slightly above the edge of the
shade. When, however, the edge of the shade is above the eye
of a person sitting in the room much more care must be used as
to the correct position of the source with reference to the shade
or reflector. A lamp at ordinary chandelier heights can only be
properly shaded when the edge of the reflector protects the eyes
from direct rays emanating from the lamp at angles in excess of
about 25 degrees from the vertical. If this rule is adopted the
310 TRANSACTIONS I. E. S. — PART I
eyebrows of the average person will shade the eyes when the
person approaches within the 25-degree zone and the reflector will
shade the eyes when the person is outside of the 25-degree zone.
Of course, this angle will vary somewhat for different individuals,
but 25 degrees is a good working average.
As to effect of color on eye efficiency and comfort little is
known save that a nearly monochromatic or one color light like
the mercury vapor is better for work on fine details.15' l6
In the lighting of small offices and desk lighting in residences
shadows play an important part in determining the satisfactory
or unsatisfactory character of the illumination from an ocular
standpoint. The more diffused the lighting the greater the free-
dom from sharp shadows. If semi-direct or indirect lighting
with luminous bowl fixtures is employed the minimum amount of
shadow is obviously obtained when the brightness of the bowl
does not exceed that of the ceiling. The more the brightness of
the bowl exceeds that of the ceiling the greater the noticeable
shadow to cause annoyance. Annoyance from shadows is not
serious, however, until the light direct from the bowl exceeds 15
per cent, of the total, as determined by Mr. T. W. Rolph.1T
The brightness of the fixture bowls in semi-direct lighting of
offices and most work rooms is limited more by the importance of
avoiding shadows than by the brightness values which will be
comfortable to face. In other words, it is usually permissible to
use a somewhat brighter bowl in a living room or dining room
than in an office.
EFFICIENCY OF LIGHT UTILIZATION.
By efficiency is meant the percentage of the light generated
which is delivered on a plane level with a common table top,
30 inches (76.2 cm.) from the floor. This depends on: (1) The
color or reflecting power of ceiling, walls and floor; (2) the shape
of the room; (3) the reflector and globe equipment; (4) the
locations of the lamps.
Color of ceilings, walls and floors may, it has been demon-
strated by Lansingh and Rolph, make a difference of over 4 to 1
in the illumination. When dealing with common colors, however,
I think a difference of 2 to 1 would be the ordinary range unless
CRAVAT H : THE LIGHTING OF SMALL INTERIORS 31 I
it is attempted to use indirect lighting with a dark ceiling when
the ratio would be very high.
A low square room will show the least loss of light by absorp-
tion and a high narrow room the greatest. In other words, the
greater the wall area in proportion to the floor area the lower the
efficiency.
The globe or reflector equipment has a great influence on effi-
ciency, but comparative figures on this must necessarily apply to
only one given set of conditions because the comparative rank
of the different equipments will change with room colorings and
lamp locations. For example, an indirect system obviously is
more affected by ceiling color than a direct system.
As to locations of lamps a central location is more efficient
than locations near the walls.
A table covering efficiencies even for the commonest of prac-
tical conditions would be too bulky for ordinary use. However,
the following will serve to give some idea of the usual ranges of
efficiency figures for certain conditions.
For a typical room 15 feet (4.57 m.) square by 9 feet (2.74 m.)
high, assuming a light ceiling in each case the light falling upon
the working plane in percentage of total light emitted by the lamp,
with the light all generated by a tungsten or gas mantle lamp at
one central outlet will be about as Table I :
TABLE I.
Efficient bowl-shaped opal or prismatic reflec-
tors at ceiling 45 to 60 per cent.
Frosted enclosing globe at ceiling 25 to 40 per cent.
Bare unshaded lamp near ceiling 30 to 45 per cent.
Indirect, mirrored reflectors 25 to 35 per cent.
Indirect, white enameled reflectors 21 to 31 per cent.
Mirrored reflector, at ceiling, deep 70 to 80 per cent.
Aluminum finished metal at ceiling, deep 45 to 60 per cent.
White enameled metal at ceiling 45 to 60 per cent.
The foregoing figures apply to clean lamps and reflectors.
In office buildings of our larger cities where soft coal is used, a
decrease of illumination due to accumulation of dirt may be fig-
ured at about n per cent, in one month in all systems where
reflectors are employed.
312 TRANSACTIONS I. E. S. PART I
ESTHETIC OR ARTISTIC EFFECTS.
This is the most difficult part of the subject in which to lay
down definite laws and establish facts for the reason that indi-
vidual tastes and opinions vary so greatly. The old saying that
'"there is no accounting for tastes" is simply one way of express-
ing the difficulty of formulating any rules regarding matters
which involve individual opinion as to what does or does not
"look well." The most that can be done is to make a few obser-
vations as to the observed trend of public opinion in some of
the more important matters relating to lighting small interiors.
First it must be recognized as a general principle that a large
number of people will not consider that any arrangement, style
or design looks right unless it corresponds closely with present
conditions. With another class of people novelty and change
rather than adherence to present conditions are sought after.
On the question of color it must be recognized that for genera-
tions artificial lighting has been done with illuminants rich in
yellow and deficient in green and blue. The only exception to
this is the Welsbach gas mantle and to judge from the state-
ments made at the last meeting of our section by Mr. Luther
that type of mantle is most popular in the lighting of small rooms
which tends to bring out the reds and yellows and suppresses the
greens and blues. It may be taken as established that any light
which does not have a sufficient percentage of red and yellow in
its composition or has too much green and blue is likely to create
a ghastly appearance of hands and faces. It also renders unat-
tractive rugs, carpets and wall paper in which yellow and red hues
are prominent.
It is a matter of controversy and personal taste and opinion as
to whether the gas filled tungsten lamp and amber tint Welsbach
mantle give a light which needs modification toward the yellow in
order to be most acceptable for common use in residences. As
these sources are considerably more yellow than any kind of day-
light it seems probable that a part of the objections to these
illuminants is due to the fact that they are whiter than the arti-
ficial illuminants to which we have been formerly most accus-
tomed, and that some of these objections will gradually become
less as the whiter types of illuminants become more common.
CRAVATH : THE LIGHTING OF SMALL INTERIORS 313
Nevertheless it must be accepted as demonstrated that the yellow
illuminants of the older types or the present illuminants modified
by globes or ceiling tints to make them more yellow produce some
very agreeable effects on complexions and on some kinds of
room furnishings. With direct lighting the color can be easily
controlled for most practical purposes by the use of the proper
glassware and for indirect lighting the color of the ceiling largely
influences the ultimate results. Such color modifications, how-
ever, always means loss of efficiency and allowance must be
made for this.
The direction and character of shadows have important effects
on objects in a room and these shadow effects have to be more
considered in small interiors where the sources of light are fewer
in number than in large interiors. Where light is largely uni-
directional, that is, direct from a small bright source with insuffi-
cient diffuse lighting to modify it, the sharp shadows which result
help to bring out wrinkles and give a harsh appearance to com-
plexion and features. Diffuse lighting either from ceilings and
walls or from windows and skylight does not in practice do away
entirely with shadows, but rather softens them to an extent which
renders the general appearance of persons and objects much more
pleasing.
As to whether there should be a visible source of light on the
lighting fixture there is no agreement. Many like to see a little
light coming from the fixture itself for decorative purposes.
Others care nothing about this.
To some the localized lighting effect produced by a dome over
the dining room table or by a table reading lamp which lights
one spot brightly and leaves the rest of the room somewhat in
shade produces a cozy effect which is pleasant. Others feel that
they cannot feel cheerful without having the whole room brightly
lighted.
Objections have been raised to indirect and semi-direct light-
ing that the ceiling is too bright and that it reverses the old order
of things too much. Others seldom think of this effect. Tastes
in these matters are largely a question of environment and
education.
314 TRANSACTIONS I. E. S. — PART I
BIBLIOGRAPHY.
1. Cravath, J. R., Brightness; Trans. I. E. S., 1914, p. 394.
2. Ives, Herbert E., The Measurement of Brightness and Its Significance ;
Trans. I. E. S., 1914, p. 183.
3. Ferree, C. E., and Rand, G., Further Experiments on the Efficiency of
the Eye under Different Conditions of Lighting; Illuminating
Engineering Society, Cleveland Convention, 1914.
4. Ferree, C. E., The Efficiency of the Eye under Different Systems of
Illumination ; Illuminating Engineering Society, Pittsburgh Con-
vention, 1913.
5. Ferree, C. E., Tests for the Efficiency of the Eye under Different Sys-
tems of Illumination and a Preliminary Study of the Causes of
Discomfort; Trans. I. E. S., 1913, p. 40.
6. Cravath, J. R., Some Experiments with the Ferree Test for Eye
Fatigue; Trans. I. E. S., 1914, p. 1033.
7. Rowe, E. B., and Magdsick, H. H., A Photometric Analysis of Diffus-
ing Glassware with Varying Indirect Components ; Trans. I. E. S.,
1914, p. 220.
8. Light : Its Use and Misuse ; Illuminating Engineering Society publi-
cation.
9. U. S. Postal Car Lighting Tests on B. & O. R. R. ; Proceedings Asso-
ciation of Railway Electrical Engineers, 1912.
10. Standard Specifications for U. S. Postal Cars issued by the Govern-
ment.
11. Cravath, J. R., The Effectiveness of Light as Influenced by Systems
and Surroundings; Trans. I. E. S., 191 1, p. 782.
12. Sweet, Arthur J., An Analysis of Illumination Requirements in Street
Lighting; Journal of the Franklin Institute, May, 1910.
13. Sweet, Arthur J., Glare as a Factor in Street Lighting; Electrical
Review and Western Electrician, Mar. 6, 1915.
14. Millar, Preston S., Some Neglected Considerations Pertaining to Street
Illumination; Trans. I. E. S., 1910, p. 653.
15. Luckiesh, M., The Influence of Spectral Character of Light on the
Effectiveness of Illumination; Trans. I. E. S., 1912, p. 135.
16. Bell, Louis; Electrical World, May 11, 1911, p. 1163.
17. Rolph, Thomas W., The Engineering Principles of Indirect and Semi-
indirect Lighting; Trans. I. E. S., 1912, p. 549.
18. Woodwell, J. E., The Intrinsic Brightness of Lighting Sources ; Trans.
I. E. S., 1908, p. 573.
19. Cobb, Percy W., Vision as Influenced by the Brightness of Surround-
ings ; Trans. I. E. S., 1913, p. 292.
IVES: DEFINITIONS, STANDARDS, PHOTOMETRIC METHODS 315
PROPOSALS RELATIVE TO DEFINITIONS, STAND-
ARDS AND PHOTOMETRIC METHODS.*
BY HERBERT E. IVES.
A series of studies in photometry, more particularly in connec-
tion with lights of different color, has led the writer to suggest
the adoption of a new standard of luminous flux and of a definite
photometric method in heterochromatic photometry. The steps
leading to these suggestions, and the arguments in favor of their
adoption, are to be found in the papers listed in the bibliography
at the end. What is here presented for publication in the
Transactions of the society is a specific set of suggestions in
tabular form, to be taken up later for consideration, if desired,
by the appropriate committee of the society.
DEFINITIONS.
Pozver consumed by a light source = P ; expressed in watts, a
portion of which is dissipated by radiation, the remainder by con-
duction and convection.
Power radiated by a source = R = I RA d\ = power emitted
Jo
by a light source in the form of radiation between wave-lengths
o and 00 , expressed in watts.
Radiation efficiency = — = ratio of the power dissipated as
radiation to the total amount of power consumed by the source.
(A pure numeric.)
Luminous flux = F = radiant power evaluated according to
its capacity to produce the sensation of light.
Light evaluating factor or stimulus coefficient of any radiation
is the ratio of the luminous flux, in its appropriate units, to the
radiant power producing it, in its appropriate units.
The luminous efficiency of any radiation = Lr = the relative
capacity of the radiation to produce the sensation of light, com-
* A paper presented at a meeting of the Philadelphia Section of the Illuminat-
ing Engineering Society May 21, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
3l6 TRANSACTIONS I. E. S. PART I
pared with the capacity of the same quantity of radiation of the
maximum possible light producing capacity . (A pure numeric.)
The luminous efficiency of any radiation is the mean
value of the luminous efficiencies of its component mono-
chromatic spectral radiations. These latter are specified
by the luminosity curve of the normal equal energy spec-
trum, of maximum value unity. The spectral luminosity
curve is obtained by the standard photometric method for
colored light photometry.
To a close approximation the spectral luminosity curve
is represented by the expression :
R3
\
La
-A(4
• e a
r
+>(.
R2
A
1 —
- e
wh
ere
A =
= 0.999
Ri =
= 0
556
B =
= 0.04
R2 =
= 0
465
C =
= 0.095
Rs =
= 0
.610
y+c(-
a = 200
/?= 400
7=1 000
Total luminous efficiency of a light source = Lt = the
relative capacity of the power applied to a light source to produce
the sensation of light, compared with the capacity of the same
quantity of power in the form of radiation of maximum possible
luminous efficiency. (A pure numeric.)
Units. — Luminous flux is connected to radiant power by a
numerical evaluating factor. The unit of power is the watt. The
present arbitrary practical unit of luminous flux is the lumen.
The light evaluating factor or stimulus coefficient is consequently
expressed in lumens per watt. If for this evaluating factor is
taken the luminous efficiency as above defined, the unit of lumi-
nous flux is the same as that of radiant power or applied power,
namely the watt.
In the symbols proposed:
PXyXLR = PXLT = F.
In order to go over to the watt as the unit of luminous flux it
is necessary to know the :
Mechanical Equivalent of Light = the value of the lumen in
watts of luminous flux.
IVES: DEFINITIONS, STANDARDS, PHOTOMETRIC METHODS 317
(The lumen is approximately 0.00162 watt of luminous flux,
or light watts.)
(The terms "specific consumption," "specific output," etc.,
involving relationships between watts and lumens, are super-
seded by the method of defining luminous efficiency, and by the
adoption of the watt as the unit of luminous flux.)
The quantities derived from luminous flux, e. g., illumination,
luminous intensity and brightness, are to be defined as at present,
with the necessary substitution of the watt of luminous flux for
the lumen wherever occurring. It is suggested that the new
unit of luminous intensity on the watt basis, might be called the
"pyr."
METHODS OF MEASURING LIGHTS OF
DIFFERENT COLOR.
Visual Method. — The visual method is specified by the type of
photometric instrument, the conditions of its use and the choice
of observers.
The instrument shall be the flicker photometer, in which the
photometric field shall be two degrees in diameter, with a sur-
rounding field of as large diameter as feasible, of approximately
the same brightness. The photometric field shall be maintained
at an approximately constant brightness of 0.013 watt of lumi-
nous flux per square meter per unit solid angle (the brightness
of a white mat surface under an illumination of 25 meter-
candles, present practical units).
Precision measurements should be made by a group of at least
fifty observers who possess no marked abnormalities of vision, or
by a group of not less than five whose average readings are the
same as those of the larger group.
(A group of five or more may be considered as constituting a
normal eye group when their average value on the following
color difference is equality.
Color A — 72 grams potassium dichromate -\- water to 1 liter.
Color B — 53 grams cupric sulphate -f- water to 1 liter.
These solutions at 20 ° C. to be contained in matched clear
white glass tanks, 1 centimeter in thickness, and measured by
the instrument and conditions above, over a standard "4-watt"
carbon lamp.)
3
3l8 TRANSACTIONS I. E. S. PART I
Physical Method. — The characteristics of the average eye may
be incorporated in a physical artificial eye, consisting of a radiom-
eter whose spectral wave-length sensibility curve is that of the
average eye.
(A close approximation to such an artificial eye is furnished
by a non-selective radiometer, over which is placed the follow-
ing solution, in a thickness of I centimeter:
Cupric chloride 60.0 grams
Cobalt ammonium sulphate 14.5 grams
Potassium chromate 1.9 grams
Nitric acid (1.05 gr.) 18.0 cc.
Water to 1 liter)
This solution should be protected from overheating by the
interposition of a layer of clear water at least 2 cm. thick.
SUGGESTIONS FOR RECOMMENDATIONS TO BE MADE
BY THE SOCIETY.
The establishment of the watt as the unit of luminous flux,
and the development of the precision physical photometer, depend
upon the exact determination of the spectral luminosity curve of
the average eye. The luminosity curve and the ratio of the
lumen to the watt have been determined with considerable ac-
curacy, but to meet the needs of the future they should be even
more definitely fixed.
It is suggested that determinations of these factors would be
most appropriately made by the Bureau of Standards, and that,
therefore, the Illuminating Engineering Society recommend to
the Bureau as specific problems of value to the science of light
measurement :
1. A determination of the average spectral luminosity curve
by measurements upon at least fifty individuals, by the photo-
metric method above specified.
2. A determination, using the results of the luminosity curve
study, of the ratio of the lumen to the watt of luminous flux.
BIBLIOGRAPHY.
The Status of Heterochromatic Photometry.
Electrical Review, Sept. 10, 1910, p. 514.
Some Spectral Luminosity Curves Obtained by Flicker and Equality of
Brightness Photometers.
Trans. I. E. S., Nov., 1910, p. 711.
IVES: DEFINITIONS, STANDARDS, PHOTOMETRIC METHODS 319
Spectral Luminosity Curves Obtained by the Equality of Brightness Pho-
tometer and the Flicker Photometer under Similar Conditions.
Phil. Mag., July, 1912, p. 149.
Spectral Luminosity Curves Obtained by the Method of Critical Frequency.
Phil. Mag., Sept., 1912, p. 352.
Distortions in Spectral Luminosity Curves Produced by Variations in the
Character of the Comparison Standard and of the Surroundings
of the Photometric Field.
Phil. Mag., Nov., 19 12, p. 744.
The Addition of Luminosities of Different Color.
Phil. Mag., Dec, 1912, p. 845.
The Spectral Luminosity Curve of the Average Eye.
Trans. I. E. S., Nov., 1912.
An Experiment Bearing on the Theory of the Flicker Photometer.
Lighting Jour., April, 1914, p. 82.
The Theory of the Flicker Photometer.
Phil. Mag., Nov., 19 14, p. 708.
kA New Design of Flicker Photometer for Laboratory Colored Light
Photometry.
Phys. Review, Sept., 1914, p. 222.
The Selection of a Group of Observers for Heterochromatic Measure-
ments.
Trans. I. E. S., vol. X, No. 3 (1915).
Experiments with Colored Absorbing Solutions for Use in Heterochro-
matic Photometry.
Trans. I. E. S., No. 8, 1914, p. 795.
Additional Experiments on Colored Absorbing Solutions for Use in
Heterochromatic Photometry.
Trans. I. E. S., vol. X, No. 3 (1915).
Physical Photometry.
Trans. I. E. S., No. 1, 1915, p. 101.
Physical Photometry with a Thermopile Artificial Eye.
Physical Review, 1915.
The Mechanical Equivalent of Light.
Physical Review, 1915.
The Primary Standard of Light.
Astrophysical Jour., Nov., 1912, p. 322.
Heterochromatic Photometry and the Primary Standard of Light.
Trans. I. E. S., Oct., 1912, p. 376.
A Method of Correcting Abnormal Color Vision and its Application to
Flicker Photometry.
Trans. I. E. S., vol. X, No. 3 (1915).
DR. CHARLES P. STEINMETZ, PRESIDENT-ELECT OF THE ILLUMINATING
ENGINEERING SOCIETY.
ALTEN S. MILLER, GENERAL SECRETARY-ELECT OF THE ILLUMINATING
ENGINEERING SOCIETY.
TRANSACTIONS
OF THE
Illuminating Engineering Society
Vol. X JULY 20, 1915 NO. 5
ILLUMINATING ENGINEERING AS A BRANCH OF
TECHNICAL INSTRUCTION.*
BY C. E. CLEWELL,
ASSISTANT PROFESSOR OF ELECTRICAL ENGINEERING,
UNIVERSITY OF PENNSYLVANIA.
Synopsis: Through the efforts of the Committee on Education the
amount of instruction in illumination given by various technical schools
and colleges has been gathered into a most interesting report covering its
investigations into the field of college instruction along these lines. Some-
what with the idea of supplementing the summary of this committee and
also for the purpose of presenting a more detailed description of the work
which has been carried out at two of the institutions investigated by the
committee, this paper has been prepared with special reference to the
illumination courses given at different times during the past three years
at the Sheffield Scientific School of Yale University and at the University
of Pennsylvania. Among the various features included in the paper are
the points which give to illumination a wide range of interest for students
in practically all courses whether academic or technical. After describing
methods used in the work for undergraduate and graduate students at
these two institutions, general conclusions are tentatively drawn as to the
best methods to follow in planning out such work, and the views of heads
of electrical engineering departments in leading universities are quoted in
their bearing on this general subject.
A number of plans have been developed during the past year
or two for broader general education along the lines of illum-
ination. These plans have included various movements instituted
by the Illuminating Engineering Society typified, for example,
by the formation of the following committees: (a) Committee
on Education, (b) School Lighting Committee, (c) Committee
on Popular Lectures, (d) Committee on Lighting Legislation.
(e) Exhibition Booth Committee (Gas). (/) Exhibition Booth
Committee (Electric), (g) Committee on Reciprocal Relations
with other Societies.
The Committee on Education also has for one of its objects
* A paper presented under the auspices of the Committee on Education at a
meeting of the New York Section, Illuminating Engineering Society. May 13, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
322 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
an effort to promote the study of illuminating engineering in the
technical schools and colleges as a general or specific branch. It
seems particularly appropriate, therefore, to present under the
auspices of this committee a brief summary of the work which
has been done at two representative universities during the past
few years in offering to undergraduate and graduate students
work pertaining to lamps and artificial lighting.
Prof. Chas. F. Scott of the Sheffield Scientific School of Yale
University has made the statement that illumination has a far
wider scope and the college has a far greater opportunity in
illumination than the training of a few specialists. Adding to
this, he continues, "There must be specialists for research, in-
vention and development, as well as expert illuminating engineers,
but their number is infinitesimal compared with those who apply
lamps and use lighting." These statements at once classify the
teaching of illuminating engineering into two broad divisions,
i. e., work especially adapted to those few who plan to become
experts either in research or practical illuminating engineering,
and, in contrast, those who must apply lamps and use light,
typical of practically every student who enters a university when
interpreted in a liberal way.
WIDE RANGE OF INTEREST.
It might seem at first thought that to make the following notes
fairly definite, reference should be made in particular to electrical
engineering students who would ordinarily have more than a
passing interest in illumination on account of its close alliance
with electrical engineering activity in general.
On the other hand a student in architecture will ultimately be
confronted with the problem of the arrangement and number of
lamps in the building over which he has supervision ; the medical
student should be interested in the relation of proper lighting to
the human eye; the mechanical engineer, who may be a works
manager in an industry, should be concerned with proper illumi-
nation in its influence on the comfort, wellbeing and working ef-
ficiency of his employees; the director of municipal engineering
may be confronted with the proper lighting of city streets; the
electrical engineer as well as the gas engineer, is vitally con-
cerned with the principles of illumination because artificial light-
clewell: illuminating engineering 323
ing may be looked upon as the basis of the electrical and gas in-
dustries; and, lastly, the average citizen, through the proper
lighting of his own home or his office as the case may be, unless
posted, is at the mercy of others in the planning of such lighting,
which from common experience is more apt to be wrong than
right.
To quote Prof. Scott in this connection, and in summarizing
these different branches of engineering study, it is only necessary
to point out in passing that a large majority of students coming
under these various heads do not expect to become illuminating
engineers or lighting experts, but in every case should be given
a training in the fundamentals of illumination, and in the rela-
tions of proper lighting to their professions.
ELECTRIC MACHINERY ANALOGY.
This statement has an analogy in a great deal of engineering
work. Thus in the study of electric machinery, the general tend-
ency has been to modify the old attitude which looked to the
training of designers, and rather to concentrate more and more
attention upon the principles which govern operation and intelli-
gent application of electrical aparatus This does not imply that
designers are not needed, but merely emphasizes the much larger
number of men who go into the operation and application side of
engineering than in designing work.
In like manner, men are required for research and development
of lamps and new methods of applying lamps, while on the other
hand a much larger number of men is concerned with the way
these lamps should be applied in practical every day cases, due to
the relation of such lighting to their own comfort, convenience
or efficiency as workmen.
THREE GROUPINGS OF THE SUBJECT.
Prof. Scott advances the idea that one way to interest students
in illumination is to get them to observe lighting conditions in
the study room, class room, lecture hall, public hall, store and
street, and to analyze the methods of this lighting and the results
which the lighting produces, always endeavoring to compare
these with ideal conditions. What constitutes "ideal" conditions
in various cases is a subject which the student should always
be asked to consider carefully. He has further presented three
324 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
ways in which the subject may be given to college students, as
follows :*
(o) For students in all departments, a few illustrative lectures pre-
senting important facts of illumination in relation to different phases of
life and indicating that the questions of lighting are not to be decided
haphazardly ; that illumination is a science ; and, above all, that there are
experts from whom advice can be secured.
(b) For students in architecture, medicine and engineering in general,
courses covering the requisites of good lighting, the kinds of lamps and
their application.
(c) For those students who expect to become experts in this par-
ticular field, an advanced and special course.
WORK AT THE SHEFFIELD SCIENTIFIC SCHOOL.
At the Sheffield Scientific School of Yale University the op-
portunity presented itself, and in making the effort to interest the
students of various courses in illumination Prof. Scott followed
several methods. One of these was to assign to the junior stu-
dents, in their seminar course, the topic of shop window lighting,
for example, requiring each student during a given week to ob-
serve as many shop windows throughout New Haven as he could
conveniently see, and to report specifically on several instances
of good and bad lighting which had come under his observation.
This scheme resulted in excellent returns; was productive of
many valuable points brought out in the seminar hours; and in-
creased the powers of observation on the part of the student,
who came to observe the lighting effect in various places where
he happened to be, more or less as a matter of course.
At these seminar hours the students also presented various
papers on lamps and lighting which were prepared beforehand
with the aid of articles and books in the reading room, and these
papers were discussed and commented upon in such a way that
valuable and interesting points were often brought out to better
advantage than could well have been accomplished by other
means.
In another case the students were asked to prepare a state-
ment of the lighting in their study rooms either in the dormitory
or private boarding house, this report to contain a plan and ele-
vation of the room or desk showing the general arrangement of
lamps, together with a summary of the various items which the
* Lighting Journal, vol. II, p. 73. April, 1914.
clewell: illuminating engineering
325
student had observed in connection with the lighting effect.
These reports proved both interesting and helpful, and in quite a
•II
fc-
f~
h- w
POSITION 0F800K
»»■ n
_#— ZSW TUNGSTEN LAMP-
OESK
ELEVATION
Fig. i.
Figs. 2 and 3.
'i; ;6.t| NOTE NEITHER REFLECTOR NOX
SHADE IS USEO.BUTANEYE
SHIELD IS WORN. NO SHAOOWS
ARE CAST
LIGHTING BY TWO 60-WATT
CARBON LAMPS
FRONT VIEW
Figs. 4 and 5.
//in -
/ '// .' 1 *
' / / I i I
few cases led the student to see that certain very bad conditions
existed which they had not before realized, and also to inquire as
to the best ways for remedying such conditions. Figs, i to 8
indicate typical diagrams which were handed in as a result of
326 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
this plan, and the following summary of the points which were
brought out by these students in their own words with regard
ELEVATION.
ELEVATION
Figs. 6, 7 and 8.
ELEVATION
to the lighting of their rooms is of interest in connection with the
diagrams and the general subject.
Fig. 1. — These views give an idea of the illumination in my study
room. My desk is 3 ft. high. Directly 3 ft. above, mounted on a hori-
zontal fixture 1 ft. in length, is an inverted lamp burning artificial gas.
This lamp consists of the inverted fixture as shown, an inverted mantle,
a globe marked B, and an outer globe marked A. The chief difficulty
seems to rest in the regulation of the flow of gas. The part directly above
the mantle generally becomes clogged with soot. The outer globe A,
which was probably made for a shade, was found to cut off too much of
the light. Now I merely use the lamp with the smaller globe B, which
affords a more intense light.
Fig. 2. — Light is intense enough and dark shadows are avoided. Also
there is no glare on the paper. Pretty satisfactory for studying, but lamps
are too low for general illumination, as they are directly in the line of
vision.
Fig. 3. — Illumination is sufficient because very little work is done
except on desk areas, which receive strong light from desk lamps. More-
over, lighting aims to be ornamental as well as useful in a study and
lounging room. Working plane is not illuminated with entire uniformity,
but this is not necessary where work is concentrated on two small areas.
However, there is sufficient light throughout room to allow of ordinary
intercourse and affairs at any point in it. Glare from desk lamps is
avoided by turning the intensive reflectors away from the eyes and by
use of non-glazed paper. The average foot-candle intensity is only 1, but
clewell: illuminating engineering 327
the light is so concentrated on the working area as to be fully sufficient
for all working purposes. Thus if the whole working plane were to be
thoroughly lighted, the intensity should be about 3 foot-candles, or three
times as much. Hence the arrangement is economical.
Fig. 4. — The lighting consists of three 40- watt, no-volt tungsten
lamps; two in a central fixture overhead, with a mounting height of
1 ft., and one desk lamp, its energy being supplied from the central fixture.
The working plane is 3 ft. above the floor. The regular intensive type
prismatic reflectors are used in the central fixture, while the desk lamp
has a green glass shade. The central lighting fixture is mounted in the
center of the plaster ceiling. The room is sufficiently lighted, the desk
lamp alone supplying sufficient light for studying and reading. Except
for the extreme corners, the whole room is rather uniformly lighted,
though the working plane could not be said to be uniformly lighted
throughout owing to the arrangement of the fixture. There is more or
less glare on the desk, due to papers, which is avoided by dispensing with
said papers and moving the desk lamp.
Fig. 5. — Neither reflector nor shade is used, but an eye shield is worn.
No shadows are cast. Lighting by two 60- watt no-volt carbon lamps.
Fig. 6. — The lamps used are all 25-watt tungstens and are eight in
number, the fixture on the table taking two lamps. The lamps on the
desks are ordinary flexible desk lamps. The reflectors are all intensive.
The illumination on the desks is sufficient, but there is a glare from the
papers. The table lamp is very poor as it is very intensive and is more
ornamental than useful. The lamps about the wall are more for artistic
purposes than for real lighting. The economy is very low.
Fig. 7. — For study, and reading close to the desk, the study lamp is
sufficient; the lamp overhead, being directly over the desk, does not add
much to the light on the desk. For reading away from the lamp, the
light is hardly sufficient, even with the overhead lamp. The light is much
poorer on the left side of the desk, since the lamp is at the right for
convenience. Glare is usually annoying, since my eyes are usually in line
with lamp and book; I usually shift the book, but it might perhaps save
time to change the lamp. I rarely use the lamp overhead; the mantle
usually gives less and less light till a new one is necessary, which is once
in every two months or so ; I should call the economy about average.
Fig. 8. — The lighting for this room was furnished by gas, burned with
mantles. An opalescent globe is used to cut down the glare, but no
reflector is used. There are but two of these lamps for the room, being
mounted a foot or more above the working surface of the desks. The
illumination is sufficient for reading and working at the desks without
eye-strain, but at a distance of 3 or 4 ft. from the lamp the illumination
is too poor even to attempt to read. Owing to the translucent globe sur-
rounding the mantle, there is no noticeable glare from papers lying on
the desks. I think that on account of the necessity of cutting down the
328 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
light from the gas lamp, it is a poor type to use for individual lighting,
and that it would have been better to have a couple of these mantles in
the center of the room equipped with proper reflectors, so that individual
lamps would not be necessary.
The foregoing statements taken from a large number of similar
opinions represent the ideas of typical senior and graduate stu-
dents before giving any appreciable attention to the subject of
lighting. The various instances cited are selected from written
reports of men in both the electrical and mechanical courses and
the opinions advanced are of special interest and importance be-
cause they show an appreciation of many illumination features,
even if expressed in a crude way, which ordinarily are not given
attention by the average user of light. The features brought
out by these simple reports are also considered important because
they indicate how readily a student takes up an analysis of a
lighting problem as simple as that involved in the lighting of his
own study room after his attention is called to the fact that there
is something to analyze.
A summary of these eight opinions indicates that the attention
collectively has been directed to items which include intensity,
shadows, glare from lamps and reflecting surfaces, general il-
lumination, regulation of gas flow, deterioration, sizes and types
of lamps and reflectors, ornamentation versus usefulness,
economy and uniformity. To me this has seemed like a consid-
erable return for practically the first inspection of a system often
consisting of one gas burner used to illuminate a desk and its
books and papers. With a physical conception of these items as
a working basis, a course in illumination should easily result in
favorable progress when related to the proper combination of
such basic items for obtaining good illumination in specific cases.
It is, of course, important to follow up a general report like
this on the part of the students with a discussion either in the
lecture or class room, and this might possibly be increased to
several such talks pointing out the various items which must be
considered if good lighting is to result.
ILLUMINATION AND MECHANICAL ENGINEERS.
In my own work given to senior mechanical engineers at the
Sheffield Scientific School, in addition to the fundamentals of
CLEWELL: ILLUMINATING ENGINEERING $2()
electric circuits and machinery, a short time was allotted to a
treatment of factory lighting in its specific relation to shop man-
agement.
The formation of this part of the work for senior mechanical
engineers resulted largely from a conference with a former
graduate in mechanical engineering who was employed in the
works management side of a Connecticut industry, and who
stated on the occasion of a visit to the university, that one of the
first jobs which he had to undertake after leaving college was
that of improving the artificial lighting in his plant. His request
for some kind of information or a reference which might lead
him to gain a little understanding of the methods of handling
such a problem seemed so clearly to indicate the necessity for
at least some work along this line for mechanical engineers that
it was decided to incorporate a short course in factory lighting
for these men as part of their work in the electrical engineering
department. This work involved one lecture and one recitation
per week for about three weeks.
COURSE FOR GRADUATE ELECTRICAL ENGINEERS.
About two years ago a specific course was outlined in illumina-
tion at the Sheffield Scientific School for graduate students in
electrical engineering. This course consisted of classroom and
problem work, and also a limited amount of lecture work. The
text book used as a basis for the course was Clewell's "Factory
Lighting" supplemented by frequent explanations and discussions
and by a number of practical problems.
The course, given as it was to graduate students, assumed a
certain degree of preparation in the physics of light, and em-
phasized more particularly the practical or application side of
lamps and illumination. In a general way the following topics
may be considered as representative of the work given: i. Types
and operating features of lamps; 2. Reflectors and their effect
on the resulting illumination; 3. The objects to be obtained from
a lighting system ; 4. Bad features of certain lighting methods ;
5. Methods of design, installation and maintenance; 6. Study of
the lighting in specific locations, such as offices, drafting rooms,
and factories.
330 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
The work was covered in one term with two exercises per
week, and in addition to the regular time allotted, illumination
tests were made in one of the rooms of the engineering building
with different types of reflectors so as to check up the predeter-
mined values of illumination intensity which had been calculated
for this same room, on a basis of the reflector distribution curves
measured by the student.
In addition to the foregoing, the Yale Branch of the American
Institute of Electrical Engineers was used as a medium on one
or more occasions throughout the year for presenting papers by
experts on artificial lighting. For example, Mr. Bassett Jones of
New York, and Mr. T. J. Litle of the Welsbach Company, came
to New Haven at different times to give talks on the subject of
illumination at such meetings. The students also had the oppor-
tunity of attending the semi-annual New Haven Branch meetings
of the American Society of Mechanical Engineers held at the
Sheffield Scientific School, at one of which Prof. Scott and the
writer presented discussions on "Factory Lighting." These
meetings gave the undergraduate student an opportunity of
getting the broader viewpoint of illuminating engineering in its
relation to practical work and they proved valuable in their rela-
tion to the efforts for promoting a wider interest in the subject.
COURSES AT THE UNIVERSITY OF PENNSYLVANIA.
At the University of Pennsylvania the formation of the new
electrical engineering department in the Towne Scientific School
in June, 1914 has given an opportunity for certain modifications
in the curriculum, one of which has been to establish a definite
course in illumination. This work has been planned for senior
electrical engineers under a course entitled "Illumination," which
extends throughout the first term of the senior year, with one
lecture and one recitation per week. The work during the past
half year has involved the solution of a number of practical
problems, one of these in particular having proved valuable.
This problem related to a given floor area with a certain class
of work. With a given type of lamp available, the problem was
to arrange a lighting plan so as to give satisfactory illumination
on the working area.
clewell: illuminating engineering 331
This scheme of solution has included both the flux of light and
point by point methods, and with a number of dark rooms and
a portable photometer outfit, the distribution curves of typical
lamps and reflectors are later to be taken, followed by the in-
stallation of these lamps in a given room. The student is then
to calculate the illumination intensity which will result on a
basis of the distribution curve which he himself has measured,
and this is to be checked up with the actual illumination as meas-
ured with the portable photometer, as a part of the regular
laboratory course supplementing the recitation and lecture work.
This procedure has worked out thus far in a particularly suc-
cessful manner because of the interest stimulated by working
out a given problem, with the anticipation of following it up by
actual measurement. Obviously, also a problem like this will
bring out many points, such as the discrepancy between calculated
and actual values due to the effect of ceiling and wall reflection
and similar items.
To senior mechanical and chemical engineers also some work
has been given in factory lighting as a part of their course in the
electrical engineering department, this work having been covered
in about eight to ten weeks, and involving one lecture and two
recitations per week. The interest displayed by mechanical and
chemical engineers has been increased by pointing out how good
illumination is related to efficiency of production in the kinds of
industries in which they are apt to be engaged later.
SOME CONCLUSIONS.
The writer's experiences at the Sheffield Scientific School and
at the University of Pennsylvania seem to indicate the wisdom
of taking up, first, the physical characteristics of the different
types of lamps, and, second, following this by a study of con-
ditions related to the objects to be illuminated, typified, for ex-
ample, by office or manufacturing spaces, making a careful study
of the needs of given cases and then determining which types of
lamps are best adapted to the work and how they should be ar-
ranged and installed.
The point which is intended here is a little difficult to make
clear, but is nevertheless important. A course of this kind if
332 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
made entirely descriptive, i. e.} based on existing methods of
lighting in various kinds of locations, loses force because the
average student lacks the experience and perspective to form
physical ideas of the items involved and their relative importance.
He should, during the course, be given photometric problems in
the laboratory and should make illumination measurements under
actual installations so that the stimulus produced by the element
of personal initiative is added to the interest so often passive in
merely descriptive courses.
This general principle is not limited merely to the teaching of
illumination, but applies with equal force to many engineering
branches, like that, as an illustration, of motor applications where
the physical characteristics of motors can to advantage precede
the study of the speed and torque requirements of the machinery
to be driven These specific items supplemented by numerous
problems can then be followed by other more elaborate problems
illustrating the selection and application of the motor to the ma-
chine.
Briefly, then, the teaching of illumination in its practical as-
pects seems to lend itself to the same general methods as does
that of motor applications, and a rational basis in each case seems
to be, in order of treatment :
(a) The purpose or object to be accomplished, i. e., the supply
of light (or power) as a means to an end.
(b) Physical characteristics of lamps (or motors).
(c) Physical characteristics of the location (or machine) to
which the application is to be made.
(d) A study of the conditions involved in the selection and
application of the lamp (or motor) in conformity to the pre-
liminary information gained in (a), (b) and (c).
NOT DIFFICULT TO GAIN INTEREST OF STUDENTS.
Taken as a whole, there seems to be no difficulty in gaining the
attention and interest of undergraduate students in illumination
because it is so intimately related to every day experiences. Quite
a number of men come into the office off and on with problems
which they run up against, in a dining room, or the hall of a
fraternity house, or a church, in connection with which some
CLEWELL: ILLUMINATING ENGINEERING 333
friend has asked advice; in nearly every case the man being in-
terested in the accomplishment of a certain result, which had
either been a case of bad lighting before, or in which his friends
had desired to assure themselves of a good result instead of
placing themselves at the pleasure of an architect or a wiring
contractor.
It has been found very helpful in this work at the University
of Pennsylvania to point out the present status of lighting legis-
lation in the various states throughout the country. To this end
the Committee on Lighting Legislation of the Illuminating
Engineering Society has been a distinct help, because through
their cooperation a summary of the laws in a number of states
has been made available in the reading room to which the students
go between recitation hours. From the writer's personal experi-
ence, it would seem that a great compensation awaits those in-
stitutions which undertake work of this kind, even if it be only
for accomplishing a better appreciation on the part of the student
of what good lighting consists without any regard to his entering
illuminating engineering as a special field of later activity. In a
few instances, however, undergraduate students have come to
look upon the lighting field as one of distinct opportunity.
The recent report of the Committee on Education has gone to
show that at the present time the teaching of illuminating
engineering in technical schools and universities is not by any
means standardized, nor even definite in many cases. This, how-
ever, need be no discouragement because electrical engineering
education as a whole is far from standardized; in fact it would
probably show almost as great a number of discrepancies in a
summary of other more or less time honored subjects as now
given in the various schools. The main point at issue at the
present time is rather to arouse enthusiasm for this work and to
place it on a par with other subjects in electrical engineering
courses, which either by long usage or an account of actual merit
are termed fundamental.
VIEWS OF ELECTRICAL ENGINEERING DEPARTMENT
HEADS.
The writer recently addressed personal letters to the heads of
the electrical engineering departments in a number of the leading
334 TRANSACTIONS OF IIXUMINATING ENGINEERING SOCIETY
technical schools and universities to find out how much of a field
there might be for the lantern slide talks of the Committee on
Popular Lectures before student audiences, in the hope that the
opinions expressed would indicate, at least in a general way, the
attitude of the men in the educational field to broadening the in-
formation of college students along the lines of illumination.
These letters asked specifically for two opinions: (a) the
amount of theory which should be incorporated in the popular
lectures; and (b) whether the possible use of such lectures before
classes of college students should influence the method of treat-
ment, and in regard also to the field for such lectures before
student audiences. Quotations relating to the second item are of
interest in showing something of the attitude held at this time by
the heads of representative electrical engineering departments
and the following paragraphs bearing on this particular phase of
the popular lecture movement are quoted because they bring out
some interesting points related to the educational problem.
1. I believe the average student will derive more benefit from lectures
intended for the public than from technical treatments of the subject.
Let us give them the technicalities in the class room. Even there we are
inclined to proceed too fast in our effort to cover ground in a short course.
2. I believe that such lectures will be welcome and well received in
almost any college in the country.
3. To be successful before the student body, it would be necessary to
have the treatment somewhat technical ; otherwise they would fail to hold
the respect of the students and I do not think that a technical treatment
is inconsistent with popular comprehension.
4. If the lecture does not comprise a sound basis on, and in connec-
tion with theoretical principles, I think it should not be used before college
students. To my mind one of the greatest troubles of our educational
system to-day in all its branches is superficiality and the failure to give
a thorough grounding in underlying principles. My feeling on this point
might be modified somewhat in the case of a lecture which was accom-
panied by exceptional illustrations both on the screen and on the lecture
table.
5. Since, in my estimation, the college student audience is not very
different in mental ability from the audience that would be attracted by
such lectures, I can see no good reason why there should be any modifica-
tion of the plan of the lectures on account of the probability that they
will be presented in colleges.
There are too small a number of the students in our colleges who
are taking courses in illumination. A still larger number are getting
CLEWELL: ILLUMINATING ENGINEERING 335
acquainted with the meaning of the term "Photometry" and know the
purpose of a photometer in their work in physics. Of these students a
large number may have but a hazy recollection of the subject, but I
believe those who remember will profit by the lectures. I also believe it
to be true that college students, many times, hear with pleasure and
profit, from an outsider, the same things to which they give almost no
attention if heard in class from their regular instructor.
In regard to the field for such lectures before college audiences, I
imagine it is a case in which the demand has to be created. The subject
is of the greatest importance and the colleges should be compelled to
take heed.
6. As I understand it, your object is general education and, since the
college student forms an exceedingly small proportion of the total popu-
lation of the country, I should hesitate to include modifications in the
lecture simply intended for that class.
7. Regarding the field for lectures before student audiences, I think
there is a very considerable opportunity for such lectures. For instance,
we have an hour each week at which the whole student body is gathered
to listen to an address by some outside man, and such custom is followed
in a large number of other institutions. There are a great many lectures
given before various departments of our colleges and I am sure that if
you can enlist a few well known illuminating engineers they would find
a large number of invitations to speak before college audiences. When
you consider the very large number of colleges in the country, academic
as well as technical, and the large number of young men and women who
can be reached in this way, it seems to me to offer one of the very best
fields of endeavor for the work of your committee.
8. The possible use of these lectures before student bodies should not
modify or influence their mode of treatment. The student should obtain
the same amount and the same kind of benefit as the practical man in the
one or the other business of life. The treatment should be no more
technical or theoretical in the one case than in the other. Anyhow I
should venture the opinion that for the average student in our colleges
and engineering schools much of the highly mathematical theory of some
of the subjects presented would be productive of greater results if the
time were spent in teaching how to apply the simpler mathematics and
the really usable theory. Of course, I am speaking of the average, not
the exceptional student.
Such lectures should afford the student a splendid opportunity to get
the layman's point of view— to meet him on common ground, and possibly
because of his own more complete technical training be the readier in
the application of the important principles of illumination, and thus be
in position to be of greater service as a practical engineer than he may
otherwise have been.
9- As far as the method of treatment is concerned, if these lectures
336 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
are intended for popular consumption, and for the purpose of directing
the popular mind regarding the proper methods of using lights, which is
a large and desirable field to cultivate, no subsidiary use of the lectures,
such as using them before college students, should be allowed to influence
the method of treatment. That is, if the best effect is to be expected
from these lectures as popular lectures, they ought to be planned and
executed without any deviation from their primary object.
I don't doubt that there would be a good deal of use for such lec-
tures before arts students in the colleges, and perhaps before the engi-
neering students of the weaker engineering schools, but the popular
character of these lectures would probably not injure them for that
purpose.
10. It seems to me that unless it is done with extraordinary skill, this
kind of thing is pretty sure to scare out a popular audience before the
lecture really gets started. Of course, in so far as such lectures were to
be used with college students, there would not be so much objection to
presenting the theoretical side, but even here I should think it would be
as well to confine the lecture mostly to the more practical and to demon-
strative features.
11. Lectures before classes of college students by outside illuminating
engineers ought to be of great value. I doubt, however, if they would be
of such direct value as talks before the general public. The average
student feels himself about surfeited with the work he has to do and is
not prone to hasten to lectures not required of him unless the subject is
somewhat unique or the lecturer of considerable reputation. I would
venture to suggest that the best way to get such lectures before the
students is to have them given in regular class-room time. In colleges
which have a branch of the American Institute of Electrical Engineers,
there should be no trouble at all in getting these lectures before the
student body. I wish there could be more of this done in this way. If
our student branches are to flourish it will only be when they are actively
aided by engineers and lecturers from outside.
Again, I believe that these lectures if they are to be successfully given
before our students should not go too much into the physics of the matter,
but deal largely with the practical side of the question, and should include
practical demonstrations, commercial data and the like. The college
departments can be relied upon to give the student the theoretical side of
the subject. The trouble so often is that we have only time for the
theoretical side and can spare little or no time to the practical side.
12. It would seem to me that the method of treatment should be
adapted to each individual audience. There is some field in colleges of
engineering for such lectures, but I am not able to state what the different
colleges offer in this branch of engineering.
13. I believe that lectures more or less popular before college students
may have a very beneficial influence on the practical use of light. Such
CLEWELL: ILLUMINATING ENGINEERING 337
lectures could be much more technical than those for the general public,
for the training in physics prepares the audience for understanding the
subject. How much of a field there is for such lectures before student
audiences is difficult to say, but I believe that a well illustrated more or
less popular talk would prove interesting and draw good audiences at
practically all colleges, but particularly those where the work is indus-
trial or scientific in character.
It is gratifying to find, therefore, that in a majority of cases
the heads of electrical engineering departments look upon the
availability of such lectures as a valuable aid in undergraduate
instruction work. Only a few cases have come to my attention
where the head of an electrical engineering department looks
upon illuminating engineering work as without the range of an
ordinary electrical engineering course. This may be due partly
to a different viewpoint, or there is a possibility that it may be
due to a lack of appreciation of just what has been accomplished
during the past three or four years in this important and growing
field. It it fortunate, therefore, that the Committee on Educa-
tion is at work in helping to post such cases on the actual status
of illumination at the present time.
It is no discouragement in looking over the report of the Com-
mittee on Education, to find that the number of kinds of ways
in which lighting and illumination is taught is very diverse both
in kind and in amount. On the other hand, it is most encouraging
to note that very few of the various institutions investigated can
be found which have not in some way outlined work in this field.
It is quite possible that if an investigation like this had been made
ten years ago practically no work along this line would have
been found in the various college schedules ; it seems hardly too
much to say that a corresponding summary five years hence will
indicate almost as much uniformity, at least as regards amount
of scheduled time, in the teaching of illumination to under-
graduate students as is found to-day in such subjects as electric
railways, power plants and the distribution and transmission of
power.
338 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
DISCUSSION.
Prof. Charles F. Scott (Sheffield Scientific School of Yale
University) : The significant thing in Prof. Clewell's paper on
"Illuminating Engineering as a Branch of Technical Instruction"
is the fact that the orthodox method of instruction from a text
book leading up logically from the mathematical and physical
laws of light is supplemented by a great many other methods.
The general educational work of the Illuminating Engineering
Society is contributed to by half a dozen or more committees, and
the education in the technical school is along varied lines which
have to do with the engineering principles in the application and
use of illumination, as well as the mathematical and physical and
chemical laws in accordance with which light is produced and
distributed. Illumination is fortunate in having so many rela-
tions that it admits of treatment in many ways. Furthermore,
illumination is a matter entering into the experience of everyone,
so that its importance is apparent to all and an interest naturally
arises. Interest is quite easily awakened when we find new facts
and laws and new relations with regard to things with which we
are already familiar and have assumed that we knew all about.
When a simple illustration or explanation or a little analysis
shows that conditions which have entered into our own experience
are really not satisfactory, but violate some common sense con-
dition which we had never thought of, we are apt to be startled ;
we realize that our powers of observation and simple reasoning
have not been active. In brief, illumination is a fine opportunity
for the cultivation of the observing and reasoning powers. Some-
times the highest order of invention consists in' accomplishing
something which everybody may recognize at once as the obvious
and proper thing, although they somehow did not happen to
think of it at first.
Prof. Clewell's paper, therefore, indicates new and varied ways
of technical instruction, which are of great value as a type of
training, as well as a source of information for the engineer.
Illumination, the new branch of engineering, is fortunate in
being able to give a stimulation to engineering education.
Prof. Harold Pender (University of Pennsylvania) : In this
paper Mr. Clewell describes the work conducted for two years
ILLUMINATING ENGINEERING 339
in conjunction with Prof. Scott at Yale University in giving work
in illumination to undergraduate and graduate students, also the
work of the past year at the University of Pennsylvania along
these same lines. The object of the paper, apparently, is not to
set forth the idea that these courses are looked upon as all that
could be desired, but merely to describe what has actually been
accomplished at two institutions thus far. The underlying object
of the paper has been to invite discussion which would tend to
help the author in any future work conducted in the development
of this particular line of instruction.
At the University of Pennsylvania the aim in the electrical
engineering department is to place each line of work as far as
possible in the hands of men fitted by practical experience or
special study to make them competent to plan the courses to the
best advantage. In this way the instructor is able to concentrate
his attention on relatively few subjects and satisfactory results in
such specialized courses as telephony, railways, illumination and
motor applications have thus been possible. The course in illumi-
nation involves a relatively small amount of time in the prin-
ciples of illumination, supplemented by photometric and illumina-
tion experiments in the laboratory. The laboratory is equipped
with all types of modern electric illuminants.
Mr. Clewell points out the value of a course in illumination not
only to electrical but to non-electrical students. Thus the mechan-
ical engineer from the standpoint of the future works manager
should have almost if not as keen an interest in factory lighting
as has the electrical engineer in other special lighting fields.
The fact that there is at present only a limited call for men
specially trained in the principles and practise of illumination is
largely due to a failure on the part of those in responsible charge
of shops, factories and large offices to appreciate the importance
of good illumination from the standpoint of the efficiency of the
worker. The remarkable increase in defective eyesight in the
last fifty years is probably due more to poorly designed lighting
installations than to lack of light ; it is proper distribution rather
than brilliancy that is of primary importance. A better under-
standing of the principles of illumination by all kinds of engineers
will in the long run mean not only an improvement in the "public
340 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
health," but also an actual saving in dollars and cents to the
employer of labor.
Mr. William J. Serrill : Prof. Clewell has given us in this
paper a very interesting discussion of the educational side of
illuminating engineering. In the engineering schools of the
country there is to-day noticeable a marked tendency away from
specialized courses, and in favor of a thorough instruction in
general principles that underlie all engineering. This refers to
undergraduate four-year courses. In the practise of law,
there are probably as many different branches of work as there
are in engineering. In the law schools, the instruction for all
students is uniform, and they all get the one degree of doctor of
laws. I look forward to the time when a similar situation will
exist in engineering schools. The principles underlying engineer-
ing in general will be thoroughly taught, and the one degree of
doctor of engineering will be given. The graduate will equip
himself for specialized work in a post-graduate course, or will
do so by his own efforts after leaving college.
The principles underlying illuminating engineering are of such
importance that they should undoubtedly be included among those
general principles which are taught to undergraduates. The engi-
neering school of the future will undoubtedly be equipped to turn
out a finished illuminating engineer as a post-graduate product.
The presentation of the principles and practises of good illumi-
nation before students other than those in the engineering depart-
ments is desirable, and the popular lectures which Prof. Clewell's
committee is preparing, as well as other illustrated lectures on the
subject, are undoubtedly an admirable means of spreading the
propaganda of better illumination among educated people. The
thing is to overcome the natural indifference to the question of
illumination, and to awaken an interest in this subject among the
students. Especially is it important that students in the archi-
tectural schools and those in the medical schools be made aware
of the importance of illumination as affecting the great profes-
sions of architecture and medicine. In both professions there is
great ignorance of the principles of illumination, and the most
effective way of improving this condition is to work on the
ILLUMINATING ENGINEERING 341
students in these departments, rather than to attempt to influence
the practising architect or physician.
Mr. Norman Macbeth : There seems to be a question in the
minds of many when considering the employment of graduates
as to the value of a course in illuminating engineering. To my
mind this situation is due to a failure to appreciate the value
of such a course, or perhaps to the usual conception of what
the present illuminating engineer stands for. The so-called and
self-styled illuminating engineer, who has been most prominent
in the commercial field within the past five or six years, has in
many instances been neither an engineer nor a commercial man,
and has left a deep impression in many minds as lacking more
than he possessed.
There is no disagreement as to the value or usefulness of an
electrical engineering course, and graduates find employment in
widely diversified fields of electrical apparatus design, manu-
facture or application. There is no confusion as to where and
how the electrical engineer's education may be applied. The elec-
tric railway field, telegraph, telephone and wireless, electric trucks,
power applications, etc., afford many opportunities. The course
for the electrical engineering graduate covers a wide range of
electrical applications. So far as the course itself is concerned,
however, many of these applications have been merely touched
upon, and the final usefulness of the training of the graduate
most likely comes through a specialization of some one branch.
And so it will be with the illuminating engineering graduate.
There are thousands of opportunities for trained men in the
lighting field to-day. The entire lighting field is largely in the
hands of mechanics and men quite unfitted so far as training or
an appreciation of their responsibilities is concerned. And the
results so much desired are largely based on thumb rule and
guess to say nothing about indifference.
In the United States alone in 1913 our sales of lighting equip-
ment totaled over $65,000,000 and of central station energy for
lighting over $300,000,000 per annum. It may be noted that the
central station receipts from lighting are more than twice that
from the much talked of and consistently sought power load.
Surely a business of $400,000,000 annually — and it is greater than
342 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
this if we include gas lighting — a business which is so closely and
intimately associated with our lives and with the health and en-
joyment of the people, and admittedly so ineffectively handled
to-day, presents opportunities for illuminating engineering grad-
uates.
In the applications of lamps, glassware and lighting fixtures, in
contracting and construction, there are opportunities for men who
know the fundamentals of illuminating engineering and have the
common sense to apply their knowledge. A graduate illumin-
ating engineer with a course which is at all comparable with that
of the electrical engineer, retaining as much of his course as the
average electrical engineering graduate, has vastly greater oppor-
tunities for usefulness; and it is this usefulness which in any
field commands salaries worth while.
The illuminating engineer has not as yet sold his proposition
either to the management of his company or to the general public,
but when he does, and that time is not far off, he will readily
secure his proportion of the many millions expended in this field.
Mr. P. S. Milear: The New York Section is privileged to
have presented before it this paper on the educational phases of
illuminating engineering. I am sure that we have been interested
in the accounts of the introduction of these two courses in Yale
University and the University of Pennsylvania. It seems to me,
however, that a great part of the moral of this paper must lie in
its application and that to make it most useful it must be placed
in the hands of members of faculties of colleges and universities
which might utilize it and apply it to their advantage.
It occurs to me that we are about to issue a report of last year's
Committee on Education and that it would be an excellent plan
to include copies of Mr. Clewell's paper with copies of the report.
With regard to this question of illuminating engineering educa-
tion it seems to me that there are three points of view, respec-
tively that of the educator, that of the employer and that of the
Illuminating Engineering Society. In university education it
apparently is the tendency to broaden under-graduate engineering
instruction, and to include in a graduate course such special
instruction as illuminating engineering. With reference to em-
ployees, this year's Committee on Education, under the direction
ILLUMINATING ENGINEERING 343
of Prof. Richtmyer, is planning a canvass to ascertain what
demand corporations might have for engineers who graduate
from a special course in illuminating engineering, such as is con-
templated. If I rightly understand the point of view of the
society it is that we are not prepared to urge instruction in illumi-
nating engineering at the present time. We are anxious to do
all we can to pave the way for it, and wish to be prepared to
supply such information as it is within our power to make avail-
able whenever there exists a demand for it. We want, of course,
to promote the movement, but at the present time we do not see
that the time is ripe to urge any extension of this form of
education.
Prof. Clewell's paper, it seems to me, if properly applied in
colleges and universities, is going to do much toward assisting
in creating this demand which the society wants to meet.
Prof. Arthur J. Rowland (Drexel Institute) : Educational
work in illuminating engineering is so constantly connected with
electrical engineering courses only that I am glad to note the
remarks in Prof. Clewell's paper and emphasize the fact that such
education has a far wider application. I have been constantly
surprised that, though electrical engineering courses invariably
contain a course on electric lighting, in connection with which
the study of electric lamps themselves and some study of illumin-
ation by these lamps at least are taken up, nothing of a correspond-
ing kind exists in mechanical engineering courses. It seems to
me that the place to start with training in illuminating engineering
is in the regular college physics courses. It is true that the text-
books are not adapted to this, but it is surely time that along with
the study of light the terms and nomenclature of illuminating
engineering should be introduced. The application of light for
illumination should be made at least as much of as the use of
lighting appliances to which considerable time is given in our
college physics courses.
Taking two hours per week through the senior year of engineer-
ing, a really valuable course in illuminating engineering can be
given. In the electrical engineering course at Drexel Institute
this amount of time has been given for a number of years. In it
can be included not only all the fundamental principles of illumin-
344 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
ating engineering practise, but a number of problems relating to
indoor illumination, including arrangement of lamps and circuits
to supply them, as well as a study of the various illuminants avail-
able for everyday service. Students seem to enjoy this course
very much and take hold of its practical problems with avidity,
even when considerable outside time is required of them. It
seems to me that the actual photometric and illumination measure-
ments which are to be done must inevitably be carried along as
part of the engineering laboratory work. It is impossible to or-
ganize or to spare the time for a special course in photometry and
illumination measurements.
While I believe in such a course not only for electrical en-
gineers but for others, I have grave doubts as to the real value of
such training in comparison with that found in other branches of
engineering knowledge. This is because in my experience there
is very slight demand indeed for men who have been trained
specially in illuminating engineering work. Philadelphia is a
rather large town and it is possible to judge the importance of
various engineering subjects by the demand for them in evening
class work here. For half a dozen years among the college sub-
jects offered in the evening classes, Drexel Institute has offered a
course in lighting and illumination. I have personally taught this
class, and I think I am well enough known in the Philadelphia
Section of the Illuminating Engineering Society to have as good
a chance as anyone else to secure a class. A very small class
was carried in this subject for two years. We have, however,
now decided to abandon the work since we have given up any
expectation of finding any demand for such training. There is
a much larger demand, for example, for training in telephony,
which seems to be a highly specialized line. In fact, those who
study telephony must nearly all of them of necessity hold posi-
tions with a single telephone company. There are many firms in
Philadelphia and many consulting engineers' offices in whose
business lighting and illumination plays an important part.
Nevertheless there is clearly no interest in and demand for such
courses of training here.
Prof. A. A. Atkinson (Ohio University) : The subject of
illumination offers not only a very interesting field for scientific
ILLUMINATING ENGINEERING 345
investigation, but also furnishes one of the most useful and
delightful forms of study for a great body of students, even those
in domestic science and educational courses. It takes rank in
the technical field alongside the finest lines of research; in prac-
tical every-day importance alongside hygiene, sanitation, etc.
Scarcely any other line of thought or investigation touches so
many phases of practical life, offers so many opportunities for
the cultivation of the artistic and esthetic sense, or is allied with
so many other technical professions.
The method of Prof. Scott quoted by the author of the paper
should prove an excellent means of arousing an interest in closer
and more intelligent observation of illuminating conditions and
of cultivating powers of analysis and the formation of correct
judgment. I note, however, that most of the student reports
quoted by Prof. Clewell ended with the statement of found con-
ditions only. I believe that senior and graduate students should
be required to draw conclusions from their observations as to
methods of improvement of the conditions found and reported,
and even to propose plans showing how they would proceed to
make the modifications suggested.
The general course outlined by the author as the result of his
experiences in teaching the subject seems to be an excellent mode
of procedure. The combination of the observational and descrip-
tive phases, calculations based on specified conditions, and finally
actual illumination measurements both in the laboratory and
factory should make up a course, when supplemented by lectures
given by experts engaged in practical illumination, of great edu-
cational value and absorbing interest to every student.
I hope the time will come shortly when the teaching of this very
interesting subject will be very general and uniform in the col-
leges throughout the whole country.
Mr. R. E. Simpson : Graduates of mechanical and electrical
engineering departments of our technical schools and colleges are
very often in a position in which they are called upon to approve
or disapprove the present lighting system, or a new lighting
system, in a factory. Much more than the mere saving of a few
dollars on the monthly lighting bill is dependent on the decision
made. Generally speaking, the increase or decrease in the light-
346 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
ing bill should not be the determining factor, for this is of minor
importance when the ultimate results are considered. Decrease
in spoilage and seconds, increase in production and efficiency of
the workmen, and the safety of the employees are of far more
importance than the saving in the lighting bill. Referring to the
last one of these items, namely, the safety of the workmen, the
influence of the lighting installation may be felt in the profit and
loss item because of damage claims. Assuming that an engineer,
because of his unfamiliarity with illuminating engineering, should
decide on a lighting system that will not provide proper illumina-
tion for the work, but which will save an average of $25.00 per
month compared with the cost of the old system. He then will
have saved his company $300.00 per year, provided no one of
the workmen is injured because of the inadequate or improper
illumination. At the present time I am gathering statistics on
illumination and accidents and although the investigation has
only recently been started, the average of the figures so far
obtained indicates that the cost of one accident would more than
offset the saving in the lighting bill for the year. Any additional
accidents which might be charged to the lighting conditions
simply add so much more to the cost of the illumination. In
states having workman's compensation laws the question of acci-
dent prevention is a matter of real concern to the factory owner
or manager. It is decidedly to his interest to keep informed on
every item that enters into accident prevention work. The
mechanical or electrical engineering graduate who intends to
enter the manufacturing field should therefore have as thorough
training in the fundamentals of illuminating engineering as in
other subjects, if in him is to be lodged the authority to pass on
lighting questions, as well as on other engineering matters.
Prof. W. E. Barrows (University of Maine) : I have read
Prof. Clewell's paper with much interest and at this time I wish
to express my appreciation of the good work which the Committee
on Education is doing.
It was my privilege to give the course in illuminating engin-
eering at the Armour Institute of Technology in 1907 when the
subject was offered there for the first time, and I have been
teaching that subject each year since that time. When I became
ILLUMINATING ENGINEERING 347
associated with the University of Maine, the electrical course was
changed somewhat, and the subject of illumination added to those
of the curriculum. It was received with interest and has proved
a success.
One of the features of the course which has received much
attention has been the arrangement of the subject matter of the
course so as to secure the greatest amount of interest on the
part of the students and, at the same time, cover the subject in
a logical order.
While using my book "Light, Photometry and Illumination"
as the basis for the course, it has seemed advisable from the
standpoint of interest on the part of the class to first take up in a
general way the subject of illuminants in their different forms,
together with their characteristics and uses. By so doing, the
student at once becomes aware of things more general than he
had learned in physics and is keen to refer to these illuminants
when taking up the fundamentals of luminous radiators, photom-
etry, illumination calculations and interior and exterior lighting.
It has been found valuable to assign a certain lighting instal-
lation to each student to study, criticize, redesign and discuss.
The reports are then taken up in the class and there discussed.
The results have been valuable and interesting. Several of the
fraternities have halved their lighting bills, and the dormitories
exhibit the recent lighting systems using various devices from a
new tin dish to a mirror reflector for the indirect lighting
system.
I believe there is an excellent field here in Maine for popular
lantern slide lectures not only before student audiences but be-
fore commercial and business organizations throughout the state.
The vast amount «of available water power in this part of the
country, with prospects of additional development in the near
future, indicate low rates and there must follow a more extensive
use of electricity for lighting purposes. Moreover, the practise
with regard to lighting equipment is in general not in accord with
the times. This should make an excellent field for the illumin-
ating engineer.
Prof. Alan E. Flowers (Ohio State University) : Mr. Cle-
well is to be congratulated for giving an excellent description of
348 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
successful courses in illumination. I am strongly inclined to
favor placing courses dealing with specialized branches of engi-
neering in the graduate school, as was done with the course in
illumination at Yale, but I think that every engineering curri-
culum should include a general engineering course extending
throughout the senior year, which would include a brief treat-
ment of each of the important engineering fields, in such a way
as to bring out their interrelations, relative industrial and techni-
cal importance and their possible future developments. This
course should consist of lectures, correlated reading and problems.
Illuminating engineering should find a place in this general course
and its treatment should be designed to give every student a grasp
of the principles of illumination, some conception of the im-
portance of good illumination and some idea of the magnitude of
the technical work being accomplished in this line and what the
professional prospects would be for a man entering this field.
Dr. Clayton H. Sharp : The paper by Mr. Clewell is a most
useful one, both on account of the information which it brings
together and of the practical ideas which it contains. The teach-
ing of illuminating engineering is making its way in our techni-
cal schools with certainty, but perhaps not with the rapidity
which we should wish for. The reasons for the latter condition
may be, beside natural inertia and indisposition of men to take
up new things, and the lack of time both on the part of the
instructors and the students for treating them, first, that the
importance and the many-sidedness of the subject are not entirely
appreciated on the part of the instructors, and second that the
point of departure and method of attack in teaching the subject
have not been indicated in a sufficiently definite and practical way.
In both these regards the hints contained in Mr. Clewell's paper
should be most helpful. When it is fully realized that illumin-
ating engineering presents a field which touches the every-day
life of everyone more intimately than any other branch of en-
gineering, with the exception of heating and ventilating, and
when the educational value of a course in illuminating engineering
in training the observational faculties, the judgment and the use
of common-sense on the part of students, as well as their ability
to make precise measurements along lines where only in recent
ILLUMINATING ENGINEERING 349
years it has come to be realized that measurements are both feas-
ible and necessary, the progress of the teaching of this subject
should be greatly accelerated. It seems to me that Mr. Clewell's
paper should be of very great assistance to the propaganda car-
ried on by the Committee on Education of this society and that
a great many copies of it might be used to good advantage for
this purpose.
Prof. F. K. Richtmyer (Cornell University) : The paper is
particularly interesting to me not only because of the excellent
material, which is a valuable contribution to the subject, but more
important still, from the broader standpoint, because of that for
which the paper stands: a pedagogical experiment. We need
more experiments of this kind, and less generalization as to the
methods to be employed in teaching.
Prof. Clewell has mentioned the keen interest shown by stu-
dents of illumination. I have found a similar attitude among
students whom I have taught. And not until recently, did I
realize the reason. Those of you who are familiar with college
students, say seniors, know that they have reached a point in
their educational career where they like to criticize. When you
send a student on such an expedition as Prof. Clewell has de-
scribed, to investigate conditions of lighting in shops, stores, show
windows, etc., he finds so much to criticize that he is perfectly
happy. It is not difficult to get his interest. Twenty years from
now, when you engineers have standardized lighting practise, so
that there are not so many "glaring" examples of poor lighting,
you will probably make it more difficult for us teachers to interest
our students.
There is one point regarding which I would like Prof. Clewell's
opinion: where, in the course of the instruction is the proper
place to introduce some of those things which the engineer does
not meet in his curriculum? I refer to the close connection be-
tween illuminating engineering, and architecture, physiological
optics, psychology, art, etc. For example, it is obvious that
every illuminating engineer should know something of archi-
tecture. Yet how can we make the student appreciate the archi-
ectural principles involved when we who teach him have never
had a course in architecture ourselves ?
3
350 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Prof. Clewell has mentioned the difficulties encountered in in-
teresting the directors of educational institutions in instruction in
illuminating engineering. I think the reason is not so much due
to the jealousy with which each professor guards his subject, as
to the point brought out by the comments of Mr. Serrill, as read
by the chairman. Your practising engineer of to-day, in order
to be a real successful engineer, must be more or less of a spec-
ialist, and just in so far as he must be a specialist, his education,
his fundamental education, must be broad. Our colleges are
therefore compelled to cut out a great deal of specialization in
the course of instruction and in its place put broadening subjects
— a more sure foundation for work which is to follow. In a cer-
tain university for example we used to have courses in marine
engineering, in railway mechanical engineering, in steam power
engineering, in gas power engineering, mechanical engineering
and perhaps a half dozen other courses in which the student was
supposed to specialize in his senior year. These have been prac-
tically all cut down to two or three branches and at the present
time there seems to be little room, little tendency, for branching
out again by adding a course in illuminating engineering. It is
assumed that the young engineer, in the first few years of his
practise, will on his college course as a basis, build up a knowl-
edge of his specialty. But there is this difficulty. It seems to
me that the course in illuminating engineering is not quite on a
par, so far as instruction in mechanical engineering is concerned,
with courses in say marine engineering or railway mechanical
engineering because there are so many factors — architecture,
physiology, psychology, and so on — which the student does not
meet in his general course, and which he is, therefore, not
familiar with when he comes to his professional practise.
Proe. C. B. LePage (Stevens Institute of Technology) : I
have followed Prof. Clewell's paper very carefully and believe
it to contain many very valuable suggestions for those of us who
are teaching illuminating engineering or its related subjects. This
paper is certainly a very clear and concise report of some good
work which is being actually accomplished. I expect to study it
with a great deal of interest and I desire now to thank Prof.
Clewell for presenting it at this time.
ILLUMINATING ENGINEERING 351
At Stevens Institute of Technology we have, as yet no con-
nected course in illumination. During the sophomore year we
give the students the physics of light, photometry, and illumin-
ation by lectures, recitations and laboratory exercises. This work
is followed in the senior year, by lectures on the modern light
sources and laboratory work in distribution measurements, all
given as part of the electrical engineering laboratory course. All
our graduates, as you know, receive the degree of mechanical
engineer.
Prof. C. E. CeEwell (In reply) : It has been very interesting
to me to hear the various views brought out in this discussion,
and in particular to hear from Prof. Scott and Prof. Pender.
Both of these men stand for new electrical engineering depart-
ments in two of the largest universities in the country, and it is
significant that they have manifested, as their discussions show,
a decided interest in illumination as a branch of technical in-
struction.
Mr. Semll's suggestion that the coming engineering curri-
culum will probably lead to a degree in engineering is certainly
somewhat of a departure from the ordinary views of college
education as manifested by present specialized courses. How-
ever, if one keeps pace with the times, he cannot fail to see that
engineering work in the schools is coming more and more to be
looked upon as a training in the broad fundamentals of engineer-
ing, rather than to separate the courses into electrical, mechani-
cal or civil engineering as the case may be. These different
courses will doubtless continue under the jurisdiction of given
departments, but at the same time the concentration on funda-
mentals of engineering in its broadest sense can receive due at-
tention.
Prof. Rowland's statement that in his evening classes he has
found no demand for illumination work must be looked upon, I
believe, from the standpoint of the call for particular lines of
work which normally follows the demand for men trained in these
directions. As Mr. Macbeth has pointed out, there is a proba-
bility that in the future there will be a great demand for men
trained in this field, and when such a time arrives, the demand for
illumination courses will follow as a logical result.
352 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Regarding Prof. Atkinson's suggestion that in reports like
those mentioned in the paper conclusions should always be in-
cluded by the student, it should have been stated that in these
particular reports conclusions were added although they formed
no part of the paper.
Prof. Barrows calls attention to the importance of proper ar-
rangement of work in engineering courses so as to secure the
best results. This feature coincides exactly with my own views
as outlined in the paper.
I want to express my appreciation to Prof. Richtmyer for his
comments on the paper and in particular for the fact that he
classes the work back of the paper as an educational experiment.
This is the manner in which the work has been looked upon
during the past three years and his view that it is both stimulating
and healthful in educational work to have such experiments from
time to time seems most appropriate. Answering Prof. Richt-
myer's question as to the proper place for the introduction of the
kinds of things which do not normally find their way into the
engineering curriculum, such as architecture and psychology for
example, the student branches of the national engineering so-
cieties might well be used as an opportunity for lectures from men
in these other lines of educational activity.
It was not intended in the introductory remarks of the paper
to give the idea that the jealousies of college professors are re-
sponsible for the difficulty in finding room for new lines of in-
struction work. As pointed out by Prof. Richtmyer, college
courses are already too crowded in many cases to warrant more
than the broad fundamental items which are required by the
future specialist. There must then be a good and sufficient rea-
son when one or another existing courses are replaced by some-
thing which is new and different.
In conclusion, the approval which Mr. Millar has placed on the
efforts which have resulted in this paper is gratifying and if the
material should be considered by the Committee on Education
of sufficient interest to be sent out as a supplement to the annual
report of that committee, this may be the means for hearing from
others who receive the paper and who may be in a position to
offer new and improved ways for conducting this particular line
of educational work.
OPTICAL PROPERTIES OP DIFFUSING MEDIA 353
THE OPTICAL PROPERTIES OF DIFFUSING
MEDIA, I*
Synopsis: This report is the first of a series dealing with the classifi-
cation of diffusion and the general properties of diffusing materials. The
reflection and transmission of light is either specular, semi-specular, semi-
diffuse or diffuse. These four classes are defined and illustrated. Defi-
nitions of turbidity, gloss, glare, density and other terms are suggested.
The various kinds of data obtainable and required in practise are out-
lined. The theory of contrast is given, and finally the physical theory of
scatter.
TYPES OF DIFFUSION.
Light reflected from or transmitted through various materials
is scattered in varying degree. Part of the light may be highly
diffused and the remainder reflected specularly, as in a mirror,
or all the light may be more or less scattered. Further, the dif-
fusing properties of many materials vary markedly with the
quality of the light. Colored objects with surface polish, specu-
larly reflect all wave-lengths, but the ratio of diffusely to specu-
larly reflected light is much greater for the color exhibited. Thin
opal transmits a red image of a lamp filament, but viewed through
opal and a blue filter no specular image of the filament is seen.
It is convenient in treating diffusion to distinguish four quite
distinct glasses.
1. Specular Reflection and Transmission. — Specular reflection
is exhibited by plane polished surfaces not scratched, dirty, wavv,
nor, if not opaque, reflecting diffusely from within the surface.
Bodies transmit specularly if their surfaces are plane and clean
and if they contain no imbedded diffusing bodies or particles.
Scratches, dirt or undulations on surfaces or imbedded particles
in a material produce diffusion in general only if their least
dimension be large compared with half the length of a light wave;
i. e., a quarter of a thousandth of a millimeter or a hundred
* Report No. 2 ot the I. E. S. Committee on Glare, submitted in March, 1915.
354 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
thousandth of an inch. Smaller irregularities may absorb but
never scatter light. Larger irregularities produce diffusion of
either the second or third type.
The brightness of a specularly reflected image is equal to that
of the source of light, viewed on a line through the point of in-
cidence, times the reflecting power of the surface. Reflecting
powers range from about 0.02 for water to 0.064 f°r glass> and
from 0.16 to 0.98 for metals. A specularly transmitted beam suf-
fers loss by reflection from surfaces and from internal absorption.
Transmission, T = (1-R)2 (i-A) = Tx T2 say, the quantity -log
T2 or -log (i-A) is proportional to thickness.
2. Partly Specular Diffusion. — Any reflection or transmission of
light in which a distinct image of the source may be seen is
classed as partly specular. A dusty mirror or a sheet of glass over-
0 10 20 30 40 50 60 70 80 90°
Fig. i. — Types of partly specular reflection and transmission.
lying paper exhibits typical semi-diffuse reflection. Correspond-
ing examples of transmission are given by atmospheric haze and
by glass or ice filled with bubbles. Of the original incident beam
a fraction is absorbed, another specularly reflected or trans-
mitted, and a third scattered in all directions in various propor-
tions.
In Fig. i are plotted distribution curves typical of reflected or
transmitted beams of light in which some specular remains. The
projecting knobs represent the residual specular light, their width
being the angular width of the source and their heights propor-
tional to the coefficient of specular reflection. Their area rela-
tive to the total area is the fraction of the reflected or transmitted
OPTICAL PROPERTIES OF DIFFUSING MEDIA
355
beam that is specular. The various types of semi-specular dif-
fusion differ in ratio of diffuse to specular light and in distribu-
tion of diffuse light. Each curve is from actual data. In colored
materials these curves vary greatly with the quality of the illum-
ination.
3. Nearly Diffuse. — Reflection and transmission are classed as
nearly diffuse when the specular image is completely broken up,
yet the diffusion is far from complete. The reflection from calen-
dered papers and other wavy surfaces and the transmission
through ribbed and chipped glass and oiled paper are of this
class. Typical distributions are illustrated in Fig. 2.
Diffusion varies from high and nearly uniform to that which is
nearly all confined to very near the specular angle.
10 20 30 40 50 60 70 80 90"
Fig. 2. — Types of semi-diffused reflection and transmission.
With this class of diffusion any quantitative definition of
glossiness or of glare must be arbitrary for there is no truly spec-
ular reflected or transmitted light. It might be agreed, for ex-
ample, to take the ratio of the light within io° of the specular
angle to the total in certain cases, say focusing screens. This
would doubtless be advantageous in comparing materials of the
same class, but definitions rational and useful for all classes of
materials seem out of the question.
Probably the most scientific analysis and specification of non-
specular beams would be to treat them as aggregates of miniature
specular or semi-specular beams. An analysis of the beam would
thus give by deduction the surface of internal structure of the
surface producing it. For a wavy surface we should thus derive
356 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
a mean amplitude and period; for a surface composed of minute
planes we should be led to a probability law of angular distribu-
tion. However interesting such analyses, they would be of little
practical value compared with the distribution curve itself. An
outline of the theory of the action of such aggregates is given at
the end of this report.
Both reflecting power and coefficient of transmission vary with
both the angle of illumination and angle of reflection or trans-
mission. Mean reflecting power is the ratio of total reflected to
total incident light for any given (say perpendicular) illumination.
Absolute reflecting power is the ratio of reflected to incident light
when the incident light is perfectly diffuse. The mean and ab-
solute coefficients of transmission are similarly defined.
Certain arbitrarily defined quantities are useful in comparing
materials of the same class. With perpendicular illumination,
brightness is measured at angles of o°, 45 ° (reflected), 1350 and
1800 (transmitted), B450 : Bo° is a measure of entrant scatter,
B135 : B180 of exit scatter (v. infra).
4. Diffuse Reflection and Transmission. — When a surface that
is uniformly illuminated appears equally bright viewed at all
angles of reflection or transmission, the reflection or transmission
is perfectly diffuse. Blotting paper, felt, snow and other masses
of fine crystals exhibit nearly perfect diffuse reflection. Good
opal glass and a few other materials give nearly perfectly dif-
fuse transmission.
The reflecting powers of some diffusely reflecting surfaces is
independent of the angle of incidence, in others not. The dif-
ference appears to be due to the shadows cast by minute pits or
projecting particles. When these are present, oblique illumina-
tion is accompanied by a decreased brightness on the side away
from that on which the surface is illuminated. Surfaces of crys-
talline powders formed by pressing with a plate of glass are quite
free from this effect and also from specular reflection.
PROPERTIES OF MATERIALS.
Granular Glare. — Direct sunlight reflected from the wavy sur-
face of water or transmitted through ribbed glass gives typical
granular glare. The brilliant points or lines are such as reflect or
transmit specularly while the intervening spaces are of much
OPTICAL PROPERTIES OP DIFFUSING MEDIA
357
lower brightness and give highly diffused light. Intrinsic bril-
liancies and contrasts are met with as excessive as those met with
in filament lamps without diffusing screens and just as objection-
able.
The size of grain that is tolerable depends upon the degree of
contrast. Halftone dots with a contrast of but 20 : 1 are quite
unobjectionable but brilliant points of similar angular size would
be intolerable. Excessive contrasts are tolerable only when the
angular size of grain is below the resolving power of the eye or
about half a minute of arc in angle.
Measurements may be made upon either average brightness
or brightness of detail and the results specified either as a glare,
a contrast or a brightness distribution. An image of the surface
is either magnified or diffused if required for measurement.
Thickness of Diffusing Layer. — Diffuse reflecting power in-
creases steadily to a fixed maximum value with increasing thick-
ness of diffusing medium. Diffuse transmission increases rapidly
to a maximum then decreases to zero for thick layers.
R CB
^tfLtcTToNT"
T_MMt/
^
^^0^
' THICKNESS
Fig. 3. — Effect of thickness on diffusion.
Fig. 3 indicates graphically the variation with thickness in a
typical case. Similar curves have been obtained on thin wedges
of opal glass illuminated perpendicularly and viewed at angles
of 45 and 1350 from the normal.
Reflecting power follows closely the simple exponential law:
R = Roo (1 — e ~ki) constant k being a measure of the turbidity
of the material and R^ the maximum reflecting power attained
with increasing thickness of material. The diffuse transmission
358 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
also appears to follow an exponential law, but not so simple a one.
In the theory of diffusion given below these exponential laws are
deduced from simple assumptions as to the nature of scatter.
Suppose a light flux I0 is incident on the first surface. I0 R is
reflected and I0 — I0 R or I0 (1 — R) enters the surface. Of this,
I = TI„ (1 — R) is transmitted to the back surface. The
transmission T is computed from I.I^and R, all three of which
are measured. T = I/I0 (1 — R)
D = — log T = log O, O = i/T.
Opacity O is the reciprocal of percentage transmission. Log O
= -log T is D the density, a quantity proportional to thickness.
Specific density is the density divided by the thickness in mm.
Measurements on opal glass, piles of paper, blocks of magnesium
carbonate, etc., show that the density law holds well.
The amount that print on the back of a sheet of paper shows
through (contrast ratio) is simply related to the above constants.
The light returned to the front surface is T2R(i — R) where
the sheet is backed by a similar sheet, T2RZ (1 — R) where
backed by ink of reflecting power R* . The brightness of the
front surface is proportional to the initial reflecting power plus
this returned light. Back contrast Cb is then
R + T2R (1 - R)
* ~ R + T2R, (1 — R)*
If R is large and R,- is small, as in ordinary cases, d = 1 -f-
T2 (1 — R) to a very close approximation.
Another quantity of value in describing the diffusion of special
materials is the diffusion efficiency, the relative brightness at some
assigned angle to the brightness viewed perpendicularly. For
example, with projection screens intended to be viewed at angles
up to 300 from the normal, relative brightness at 30 and o° is a
proper measure of diffusion efficiency. With focusing screens
B170 : B180 may be used as a criterion of efficiency.
Angle of Illumination. — The ratio of the diffuse to the specular
brightness of a surface varies with the solid angle subtended by
the illuminant. That angle may in practise be anything from
almost a point (sun or Nernst lamp filament) to a hemisphere
like an overcast sky. The simple problems may be treated as
follows :
OPTICAL PROPERTIES OF DIFFUSING MEDIA
359
Specular brightness B* is equal to the brightness of the source
B0 times the coefficient of specular reflection (Rs ) or transmission
( Ts ) as the case may be. Diffuse brightness B^ is such that irBd
= B0 Rrfto for not too large solid angle o> (= area/dist.*) of source
and nearly perpendicular illumination. Both Bd and B0 are in
light units per unit area, say in lumens per square cm. B0 «» =
B0 X Area/(dist.)2, is the illumination and the factor it converts
this into brightness. For illumination at a considerable angle,
a correction for oblique incidence must be applied (by integration
of the cosine of the angle of illumination) amounting to a factor
of ^ for illumination from a complete hemisphere. In Fig. 4 is
plotted the ratio of diffuse to specular brightness with increasing
solid angle of the source of illumination.
I 2 3TT 4 5 6 2TT
Fig. 4.— Ratio of diffuse to specular brightness.
For a source of limited extent and nearly normal illumination,
therefore, the ratio of specular to diffuse brightness is
p Bj Rj ir
Bd Rd 0 *
This ratio of total to diffuse brightness is a logical definition of
spot glare. Since it depends upon the illumination as well as the
material, it is not a specific property of a surface or material, but
of its appearance under stated conditions. Glare cannot be ex-
pressed in terms of reflecting or transmitting power alone. For
a source of small solid angle such as the sun, an arc or a lamp
filament, glare may have very large values unless specular re-
flecting power be very small.
The glare from large angle illumination must be treated by
elements, since both reflecting powers as well as the illumination
360 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
varies with angle of incidence. It is always small and of little
practical importance.
Contrast is relative total brightness. Call this C, then
p Brf H~ B5
C ~ B'd + B', '
Bd and B5 being diffuse and specular brightness of one part of
the surface and B'd and B's of neighboring portions whose con-
trast with the first is to be specified. For rather small illumi-
nants we may put as above Bs = B0R5 and nBd = B0R^o), hence
_ 0)Rrf 4- ttR5
_ <oR'd + 7rR's ■
For ordinary glossy print paper and ink R^ is about 0.6 for
the paper and 0.04 for the ink. R* is about 0.02 for the paper
and 0.01 for the ink. Hence
„ _ 0.6ft) + 0.027T
0.04ft) ~T" O.Ol7r"
For a small or distinct illuminant <o is nearly zero and C = 2.
For lighting from a single window, w is about unity and C = 9.4.
For a hemispherical illuminant such as the open sky C = 6.7.
In other words, with direct lighting from a bare lamp the ink
may appear half as bright as the paper but with open sky illumi-
nation, the paper is nearly seven times as bright as the ink. In
extreme cases of glossy ink or paint on a dark matt ground, the
print may appear even twenty times as bright as the background.
THEORY OF DIFFUSION.
Certain cases of mixed specular and diffuse reflection and
transmission yield to theoretical treatment by which certain prop-
erties may be deduced from known data or insight be gained into
the mechanism of diffusion.
Specular Surfaces. — Metals reflect high (60 to 98 per cent.)
and absorb light very strongly except in very thin layers. The
non-metals such as glass, varnish, water crystals of salts and the
like, reflect weakly (3 to 5 per cent.) but transmit, if transparent,
practically all the light incident except that lost by reflection.
Between these two classes of materials there is a wide gap
in which only a few solid dyes have intermediate properties.
The reflecting power of a metal may be expressed in terms of
its refractive index, its absorptive index and the angle of in-
OPTICAL PROPERTIES 0F DIFFUSING MEDIA 361
cidence. The reflecting power of a non-metal depends upon re-
fractive index and angle of incidence. The laws of reflection and
refraction may be found in any text of theoretical optics such as
Wood or Preston. The essential characteristics are those noted
above and that the reflecting powers of metals decrease while
those of non-metals increase with increasing angle of incidence.
The cases of silver and glass are typical.
Angle of incidence
e-, „ » 10 20 40 60 80
Silver R = 0.98 0.75 0.70 0.70 0.70 0.70
Glass 1.5 R= 0.04 0.04 0.04 0.045 0.085 0.20
Reflection from an interface between non-metals depends upon
the relative refractive indices of the two media (say varnish and
glass) and at the same angle is equal on the two sides. Between
a metal and non-metal (silver on glass, say) the laws of reflection
are not yet fully developed but the reflection is in amount much
as though the non-metal were not present.
The reflection from a rough surface such as a powder, a mass
of crystals or a scratched surface is simply an aggregate of re-
flections from the small elementary faces according to the laws
for large plane surfaces, except when the elementary faces are
small compared with the length of a light wave. In the latter
case the reflected waves tend to fuse together as though reflected
from the general level.
Partly Specular Diffusion.— In case part of the incident light is
specularly reflected or transmitted, the remainder may be highly
or but slightly diffused. The theoretical treatment of this case is
that of the purely specular reflection or transmission together
with that of complete or partial diffusion given below. It may
be noted, however, that actual distribution curves always show
some shading off from specular to diffuse. This behavior is
hardly to be expected in the case of a dusty mirror, a hazy atmos-
phere or of a glass containing bubbles.
Partly specular diffusion is of little if any use as such but is
made use of in studying the atmosphere and the chemical forma-
tion of slight suspended precipitates. The minimum perceptible
diffusion is extremely small if sufficiently powerful illumination
is available. The brightness of the diffused light is proportional
$62 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
both to the size and to the number per unit volume of particles in
suspension.
Pure and Partial Diffusion. — Diffusion is due ultimately to
either small spherical surfaces, small plane surfaces, spherical
bubbles, wavy surfaces or small opaque particles of indifferent
form and orientation. Consider first the problem of the gradual
scatter of light in entering a diffusing medium. At any plane
element of the medium of thickness dx let
S = flux density of specular light in the direction of x
A = flux density of diffused light in the direction of x
B = flux density of diffused light backward against x
a = total area of grains in unit area of elementary plane
r = percentage of incident light reflected by each grain in all
directions.
Then, if the thickness dx of an element is of the same order as
the mean diameter of grains
dS \dx = — ks — as (k = absorptive index)
dAldx = y2 arS — % arA + }4 arB
dBjdx = — y2 arS + y2 arB — y arA.
These equations readily give
S = S0e-"!X
2A = — (i + R) RSoe-"1* — mRC.x + C, + C3
2B = -f (i — R) RS„ e -«* — wRC,* — Ct + C2
R being an abbreviation for ar\m (m = s + k) and Q and C2
being integration constants. The specular component falls off
according to the simple exponential law. The integration con-
stants are readily determined since for x =: o, A = o and for
x =1 t, the total thickness, B = o.
Diffuse reflecting power (total) is then given by the ratio of
the back emergent light B to the incident light S0 for X = o or
B mRt + (i — R) ( i — e —* )
— is.
So 2 + mRt
The reflecting power increases according to an exponential law
from o up to a maximum value B/S<? = R = ar\m (= r if k = o).
Diffuse transmission, given by A/S0 for X = /, is a more com-
plicated exponential which is equal to zero both for / = o and
for / = oo and has a maximum value for an intermediate thick-
OPTICAL PROPERTIES OF DIFFUSING MF.DIA 363
ness such that the specular transmission ratio is reduced to about
0.1.
Of the light incident on a single particle approximately half
the reflected light is reflected at angles greater than 900 from
the direction of incidence, hence in a thin layer diffuse reflection
and transmission are nearly equal. The calculations are not dif-
ficult in the case of a reflecting opaque sphere such as a mercury
globule, an imbedded bubble or a tiny crystal or opaque particle,
but are too long to reproduce here. To mention but one instance :
the light reflected at an angle of 900 from a polished sphere is in-
cident on a ring R/j/~2~ in diameter and the projected area re-
flecting light lies half within and half without this ring.
The distribution of the light reflected or transmitted by a thin
layer is to a first approximation uniform within the hemisphere
provided the scattering particles have either (a) spherical
symmetry or (b) indifferent orientation. A great many quanti-
tative investigations show this. For example, when a liquid con-
taining suspended particles is illuminated by a rectangular beam,
the brightness of the path of the beam is closely proportional to
the reciprocal cosine of the angle of view ; that is, to the number
of particles in the line of vision independently of the angle of
reflection from their surfaces.
When a diffusing layer consists of minute planes not indif-
ferently oriented, the distribution of the reflected and transmitted
light depends upon the law of orientation of the surfaces. Let p
be the fraction of the surface covered by reflecting planes in-
clined to the perpendicular at angles lying between a and a -(- da.
Then p will be the fraction of the light reflected at angles lying
between 2a and 2 (a -\- da). This function, times the reflecting
power of the surface at that angle, will be the distribution of re-
flected light. In other words the light distribution ~L(a) = R ( — )
X P ( — ), reflecting power times angular distribution but
doubled in angle.
The transmitted light is distributed in accordance with the law
of refraction. The deviation d in passing through a thin wedge
364 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
of angle a is d = a (n — /) where n is the refractive index of the
material. Hence for shallow angles
i,-w = (#_»)(±.)x>(. + 5rin).
This law applies to the transmission of ribbed, ground or frosted
glass or glass with any kind of wavy surface. Good focusing
glass shows, under a microscope, shallow spherical depressions
acting like weak negative lenses. Such glasses scatter transmitted
light nearly uniformly over an angle of only a few degrees.
In this report certain terms relating to illumination have been
used that have not yet been officially sanctioned by the society.
These are tabulated below together with brief definitions of each
indicating the senses in which each has been used.
Partly specular diffusion : partly diffuse reflection or transmis-
sion in which some pure specular remains.
Nearly diffuse reflection or transmission : that in which no pure
specular remains but in which diffusion is incomplete.
Reflecting power at any angle: brightness relative to that of a
perfectly diffusing surface reflecting 100 per cent.
Total reflecting power: ratio of total incident to total reflected
light.
Mean reflecting power: mean of angular reflecting powers with
normal illumination.
Transmission ; angular, mean, total : analogous to reflecting
powers.
Entrant scatter: brightness at 450 / brightness at o°.
Exit scatter: brightness at 1 35 ° / brightness at 1800.
Diffusion efficiency: brightness at maximum effective angle /
Bo° or B1800.
Turbidity: constant of exponential reflecting power.
Opacity: reciprocal of transmission.
Specific density: -log opacity / thickness.
Gloss : ratio of total to diffuse brightness source 0.0 1 ster-
adian.
Contrast : relative total brightness.
The terms partly specular and nearly diffuse are used only be-
cause none more fitting have been suggested and are not recom-
OPTICAL PROPERTIES OF DIFFUSING MEDIA 365
mended by this committee. The definitions of all the terms, par-
ticularly of turbidity and glare, are to be considered merely tenta-
tive. For precise definitions of glare and its sub-classes see our
general report.
For nearly all of the new matter in this report the chair-
man alone is responsible, the other members of the committee
having read the report but not having considered it in sufficient
detail to assume full responsibility for it.
The following report is to cover the practical problems of
measuring mixed specular and diffuse reflection and transmission
and of specifying the distribution of diffused light.
Nelson M. Black,
J. R. Cravath,
F. H. Gilpin,
M. Luckiesh,
F. K. Richtmyer,
F. A. Vaughn,
P. G. Nutting, Chairman.
366 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
THE OPTICAL PROPERTIES OF DIFFUSING
MEDIA, II*
Synopsis: This report deals with the methods of measurement and
the geometrical theory of diffusion. It follows a report under the same
title dealing with the general properties, nomenclature and physical theory
of diffusion media. The following reports are to give the results of
extended investigations of various classes of diffusing media by various
methods. The numerous methods discussed include laboratory methods
of investigation and practical methods for quickly determining important
constants, methods for measuring either specular or diffuse reflection or
transmission separately, in the presence of the other or of measuring the
two combined. 'The geometry of distribution photometry involved in
deducing the required data and constants from observed data is outlined.
The investigation of the optical properties of diffusing media
requires means for determining (a) the distribution of the re-
flected and transmitted light with any desired illumination (b)
the total amounts of light reflected, transmitted and absorbed and
(c) the relative amounts specularly and diffusely reflected, trans-
mitted and absorbed.
THE DETERMINATION OF DISTRIBUTION.
There is but one general method for determining the angular
distribution of the light reflected from or transmitted through
the medium studied and that is to mount the specimen at the axis
of some form of spectrometer, then determine its brightness
with a brightness photometer attached to the observing arm.
Spectrometer. — The crudest form of spectrometer will serve
since the sole requirements are a definite axis of rotation and a
coarsely divided circle reading only to single degrees of angle.
Projection screens are often investigated in situ with only a
board, a nail and a tape line to direct the photometer and deter-
mine angles of reflection.
The Brightness Photometer. — The brightness of the material
is best determined with some brightness photometer through
which the surface studied is viewed directly. If an illumino-
meter be used, that surface must be limited to a definite area and
the illumination from this on the test screen of the illuminometer
at a convenient distance is very faint. A brightness photometer
* Report No 3 of the I. E. S. Committee on Glare, submitted in March, 1915.
OPTICAL PROPERTIES OF DIFFUSING MEDIA 367
is preferable; when this is used, it should be light, compact and
of high precision.
Two forms of these have found favor and others might doubt-
less be devised. No entirely suitable brightness photometer is
on the market. The Beck "Lumeter" is perhaps the best and this
requires modification to free it from serious systematic error.
The comparison screen is in the photometer box while the surface
whose brightness is to be measured is viewed through a hole in the
comparison screen. The eye cannot accommodate to the near com-
parison screen and the distant surface simultaneously, and lack of
perfect accommodation seriously affects the brightness of retinal
image and hence the reading of the instrument. This failure to
provide for equal accommodation is by the way a very common
and very serious defect in brightness photometers. The remedy is
simply to throw an image of the distant surface into the plane of
the comparison screen with a telescope objective or simple lens.
Another suitable brightness photometer is a simple reading
telescope with comparison strip or spot fixed in the focus of the
ocular and illuminated from the side. Several forms of illumin-
ation and illumination control have been used. The use of a
miniature lamp filament for comparison strip is objectionable in
that it requires the use of a monochromatic filter for precise
work.
The Illumination. — The distribution curve obtained for any
surface depends of course upon the position of the illuminant
and the solid angle which it subtends and it is necessary to use
some definite known angular size and position of illuminant.
Those most useful are (a) nearly parallel light from an appproxi-
mately point source such as a Xernst filament or a beam colli-
mated with slit and lens and (b) a uniformly illuminated plane
area such as a plate of opal glass in front of a frosted lamp. If
1 1.3 cm. in diameter, or 10 cm. square, it subtends at 1 meter
0.01 steradian.
If the point source or collimated illuminant be used, specular
brightness rises to a high value. The illumination is checked by
observing the brightness of a magnesium block or other diffusing
surface of known reflecting power. When the plane source is
used, determinations are in terms of relative brightness of the
368 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
illuminant and surface studied. Both forms of source are about
equally useful. The collimated beam appears to have no advan-
tage over the point or line source direct, and gives the same dis-
tribution curve. The rectangular plane source is to be preferred
to the circular since the data obtained with it are more easily-
reduced.
Fluctuation in the illuminant is, of course, a serious source of
error unless counterbalanced by a similar variation in the com-
parison source. This is easily done if both are electric lamps by
putting both on the same circuit. Differences in characteristic
curves of the two lamps, control rheostats and the like do not
cause serious differential variations if the line voltage varies not
over 2 per cent.
The Data. — The brightness of a surface viewed from any angle
is a measure of the light per unit solid angle per unit projected
area of surface leaving that surface in that direction. With the
gonio photometer (angular photometer) above discussed and a
given illumination, brightness is measured at each angle in a
plane through the incident beam and perpendicular to the sur-
face. Brightness as a function of angle, B (a) say, is then
plotted. Light emitted per unit area is then proportional to B
(a) cosa, the angle being measured from the perpendicular to
the surface. If at the point observed, the illumination is all
nearly normal to the surface this emitted light may readily be
integrated by zonal elements, the ratio of the total light emitted
to the light incident being the mean reflecting or transmitting
power. The geometry of this process is discussed toward the end
of this report.
INTEGRATING INSTRUMENTS AND METHODS.
While the distribution curves of reflected and transmitted light
give all the data required, their determination requires a skilled
observer, laboratory instruments and considerable time. When
only integrated reflecting power, absorption or transmission are
required, much simpler instruments and methods are available.
Anyone or all of these classes of data may be required (1)
mean reflecting power or transmission ; i. e., the light emitted
through a hemisphere relative to the light incident in a normal
OPTICAL PROPERTIES OF DIFFUSING MEDIA 369
pencil; (2) illumination hemispherical, observing light a pencil;
and (3) both illumination and observation hemispherical (total
reflecting power or transmission).
Transmission. — Either mean or total transmission may be de-
termined by several different methods. By far the most con-
venient is to use the Konig-Martens polarization photometer,
really a brightness comparator. It has an excellent field with no
apparent dividing line. The error in scale zero is determined by
setting in both first and fourth or second and third quadrants.
Possible errors due to plane polarization in the light are elimi-
nated by reading with the instrument direct and reversed. When
desirable to set on an actual image of the object viewed, it may
be provided with a pair of the small lenses used as objectives on
a low power binocular microscope.
Uniform diffuse illumination is secured by placing a plate of
solid opal glass ground on both sides, over the end of a white
paper cylinder within which is an ordinary tungsten lamp. The
sample whose transmission is desired is placed over half the
field. With this arrangement the readings of the instrument give
mean percentage transmissions. If total transmission is desired,
another diffusing medium such as flashed opal glass is placed
over both sample and comparison field. Mean and total trans-
mission will be the same when the material is highly diffusing.
Less precise determinations may be made with any brightness
instrument such as the "Lumeter" for example. A highly dif-
fused uniform illumination is provided as above, and the sample
placed over part of the field. The relative brightness of the cov-
ered and uncovered parts of the field give at once the trans-
mission of the sample.
To use an ordinary bench photometer to measure diffuse trans-
mission it is necessary to provide a highly diffused very bright
area at one end and limit it to a definite small area. After meas-
uring its apparent candlepower, the sample is placed over it in
close contact with it (to avoid side light) and the candlepower
again measured. Great care must be exercised in avoiding stray
reflected light.
Transmission with illumination by a direct pencil is of impor-
tance in diffusing lamp globes and shades and a few other mate-
370 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
rials. This may readily be determined by illuminating the speci-
men with a known flux and determining its brightness on the rear
side in the desired direction. If the integrated light emitted in
all directions be desired, then a highly diffusing sheet of known
transmission is interposed close behind the specimen.
Purely specular transmission may be measured with practically
any sort of photometer or spectrophotometer and any source by
simply interposing the specimen between source and photometer.
Large errors due to refraction are the rule unless the specimen
is very thin and plane. If the specimen is very thick, good results
can be obtained only by having end faces very plane and by using
only very parallel light.
Reflection. — The total and mean reflecting power of surfaces
are much less readily determined than transmissions on account
of the difficulty in avoiding shadows. The only instrument of
general usefulness available for the purpose is the ring reflec-
tometer described on page 413 of the 1912 (vol. VII) Transac-
tions of the Illuminating Engineering Society. This instru-
ment measures the relative brightness of two parallel planes, one
of which is the specimen surface and the other a diffuse illumina-
tor. The planes are limited by a reflecting ring serving to return
the light which would otherwise escape at the edges. The instru-
ment gives mean reflecting power directly except when the reflect-
ing power is either very high or very low and at the same time
highly specular. The reading head is a modified form of the
Konig-Martens brightness comparator mentioned above. Read-
ing the head in direct and reversed positions gives data for deter-
mining the percentage of light specularly reflected and for cor-
recting for polarization. By a slight modification, this instrument
may be used on wall coverings in position.
To measure total reflecting power, perfectly diffuse illumina-
tion and observed light integrated over 1800 are required. A
small receiving disk is mounted half way between the two planes
at the center of the ring and the photometer sighted on the two
sides of this by means of two small reflecting prisms.
Purely specular reflecting power is determined with a bright-
ness photometer and an extended plane source. The reflecting
power of a mirror is the ratio of the brightness of the image to
OPTICAL PROPERTIES OP DIFFUSING MEDIA 37 1
that of the source at any desired angle of incidence. The specu-
lar component in partly specular reflection may be determined by
the same method, the source being made either so small or dis-
tant or weak as to give only negligible diffuse brightness or else
diffuse brightness is measured just off the specular angle and
allowed for.
Purely diffuse reflecting power may be determined by deter-
mining the brightness under a given illumination. The reflect-
ing power is v times the brightness (in candles per square foot,,
say) divided by the illumination in foot-candles. This method
is not so precise as that in which the brightness comparator is
used.
SELECTIVE INSTRUMENTS AND METHODS.
Specular and diffuse reflection and transmission may in most
cases be determined separately with sufficient precision for prac-
tical purposes without recourse to the more laborious determina-
tion of distribution curves. The three classes of partial diffusion
of importance require different treatment. These are (a) a
mixture of pure specular with pure or nearly pure diffuse light,
(b) a very slight scatter such as is caused by dust suspensions
and very light precipitates from a solution and (c) diffusion
departing widely both from the purely specular and diffuse types.
Separable Mixtures. — In separating specular from diffuse light,
one may either measure diffuse and total, specular and total or
specular and diffuse separately. With a good brightness pho-
tometer any of the three methods may be used. With an illumi-
nation of known brightness and solid angle, the specimen is
placed at a known distance and angle, then its brightness meas-
ured at the angle of specular reflection or transmission and at
some neighboring angle, arbitrarily chosen according to the class
of the material and the purity of the diffusion. Such materials
as glossy paper, polished woods and opal glasses are readily
studied by these methods.
Another good practical method depends upon the fact that
light specularly reflected at a certain angle (about 6o°) is nearly
completely plane polarized. Hence if a surface be illuminated
and viewed through a nicol prism at this angle, if the nicol be
properly oriented, the specular light may be eliminated. The
XJ2 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
phenomenon is very striking in the case of materials like polished
furniture and glossy paper. Ingersoll1 has designed a practical
instrument for measuring glare based on this polarization phe-
nomenon. The specimen is placed on the bottom of a box and
illuminated at the proper angle by an opal window at one end.
It is viewed through a polarizing ocular at the other end. With
this instrument either relative diffuse and total brightness or
relative specular and diffuse reflecting power may be determined.
Ingersoll's instrument or some modification of it promises to
be useful for practical purposes when properly used. It should
be noted, however, that (a) it gives a 'minimum, value of the
specular reflection, if a surface is quite wavy or rough a crossed
nicol does not cut out all the specular light; (b) it does not apply
to metallic surfaces, these not reflecting plane polarized light, and
(c) it is committed to a particular angular illumination; namely,
that of the window supplied. Since the ratio of specular to total
brightness varies wi,th the solid angle of illumination, different
sizes of window will give different values of gloss.
In using the ring reflectometer (see above) the readings with
the instrument in direct and reversed position differ by double
the mean percentage polarization, hence give a measure of per-
centage specular reflection. This method gives fair results in
practise. Another method is to use the ring reflectometer to
determine total reflecting power and some other instrument such
as the modified Bechstein2 to determine diffuse alone.
An ordinary bench photometer with a Lummer-Brodhun head
may be used to determine diffuse reflecting power at perpen-
dicular incidence of certain materials3 such as paints and papers.
The photometer screen is replaced by a double one, half of which
is of the ordinary material, and the other half is faced with the
material to be investigated.
Slight Turbidity. — The amount of light scattered by atmos-
pheric haze, photographic negatives, light chemical precipitates
and other similar agents is proportional to the size, number and
reflecting power of the reflecting particles and to the intensity of
illumination. The brightness of a slightly scattered beam is
1 Electrical World, March 21, 1914.
2 Trans. I. E. S., Vol. IX, p. 611, 1914.
3 Louis Bell, Electrical World, Jan., 1915.
OPTICAL PROPERTIES OF DIFFUSING MEDIA 373
determined by some form of brightness photometer or compara-
tor. Precision, of course, depends primarily upon the intensity
and constancy of the illumination and the thickness of the
observing path. Direct sunlight is, of course, by far the best
illumination. In photographic negatives the scatter is so great
that it may be determined by measuring specular and total trans-
mission by ordinary methods.
P. V. Wells of the Bureau of Standards4 has designed a "tur-
bidimeter" for measuring slight diffusion in solids, liquids and
gases. Mecklenberg and Valentiner5 have designed a somewhat
similar but very elaborate instrument primarily for liquids. Both
instruments determine the relative intensity of direct and scat-
tered light. T. W. Richards has designed a turbidity comparator
which he calls a "nephelometer." The liquids are contained in a
pair of silvered test tubes illuminated from the side through slits
in the silver. Atmospheric scatter has been studied by Diercks,6
the photometer being pointed at various angles from the limb
of the sun. He found a drop to nearly pure diffusion at about 4°
from the sun, the brightness at that point being on moderately
hazy days, about one ten-thousandth that of that solar disk.
Inseparable Mixtures. — Very rough materials in which there
is more or less regularity of distribution give all forms of dis-
tribution curves and any distinctions between specular and diffuse
reflection or transmission must be quite arbitrary. Nothing but
the distribution curve itself can give an adequate description of
the effect of the material on a beam of light. In particular
classes of materials, brightness observations at particular angles
give sufficient data for practical purposes as shown in the pre-
ceding and following reports. Some form of good brightness
photometer, means of illuminating with a known source at a
known angle and of observing at a known angle are essential.
THEORY OF DIFFUSION PHOTOMETRY.
Nomenclature. — In dealing with the theory of diffusion meas-
urements it is convenient to depart somewhat from the accepted
nomenclature of engineering photometry and define flux and
brightness in the simplest physical terms.
4 Ph. Rev., 1914, p. 396.
6 Zeit Inst., 1914, p. 209.
6 Ph. Zeit, 1912, p. 562.
374 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Physically, light quantity is radiant energy times visibility.
Flux is the rate in ergs per second (or in watts) times visibility
at which light streams through or upon a given area. The
density of this light stream, as it passes a given surface, is the
flux per unit area. Its concentration is the flux per unit solid
angle. A beam of light is made up of a great many pencils of
light, hence the density of light on a given surface is the integral
of the concentration over a hemisphere.
The brightness of a given surface to the eye, when viewed in
a given direction, is proportional to the flux within a cone filling
the pupil of the eye at one end and coming from an elementary
projected area at the other and hence proportional to the light
leaving a given projected area in a given direction. Brightness
is then measured by the flux per unit solid angle per unit pro-
jected area of surface. The unit of brightness, the lambert is v
candles per square centimeter of projected area.
Distribution Curves. — When a surface is illuminated by light
of a known density and concentration, the readings of a bright-
ness photometer sighted on it at various angles may be plotted
as a function of angle B (a) giving a distribution curve. The
scale of the photometer is checked by sighting it on a surface of
known brightness; that is, a surface of known reflecting power,
diffusion and illumination. The brightness photometer will then
read in flux per unit solid angle per unit projected area on any
surface viewed at any angle.
In practise the photometer is sighted on a block of magnesium
carbonate whose reflecting power (about 86 per cent.) has been
determined with an absolute reflectometer. When such a block
is illuminated perpendicularly with a flux density D, the total
flux outward is RD, R being the reflecting power of the surface.
If the surface is perfectly diffusing, the flux density in a direc-
tion perpendicular to it at a distance r from it will be RD/nT2
for each unit area of the reflecting surface. Hence the flux per
steradian will be RD/V in that direction. Therefore, the bright-
ness of the comparison block so illuminated will be in any direc-
tion RD/tt flux units per steradian per unit projected area,
lamberts for short. If, then the brightness photometer sighted
on the surface measured reads B/R times as bright as on the
OPTICAL PROPERTIES OF DIFFUSING MEDIA 375
comparison block, the brightness of the surface is BD/rr lamberts
in that direction.
The angular relations involved are angle of view (a) and solid
angle w. In Fig. 1 let a be the half angle of a cone of solid angle
w intersecting the surface of a sphere of radius r. The area of
the surface intercept is 2irr* (1 — cos a) hence o> = in ( 1 — cos a)
and dm = 2v sin a d a.
Fig. 1. — Solid angle and angle of observation.
Let the concentration of light in a narrow axial pencil be C
coming from a small plane area of diffusing surface. Then the
flux within a solid angle w will be
F„ = JC cos a do> = C (o — — )
the element of flux dV within an element of solid angle du> is
therefore
dF = 27rC sin a COS a da
(' - T>
Our data then consist of a series of brightness readings B(a)
at various angles and a single reading B0 on a comparison block,
the incident normal flux density F0 being known. B(a) is plotted
as a function of angle as in the middle curve Fig. 2. This is pro-
portional to the emission per unit projected area, multiplied by
cosa it gives the lower curve, of which the ordinates are pro-
portional to emission per unit area.
Multiplying further by 27rsina gives the upper curve the ordi-
nates of which is proportional to the light emitted in a cone
element of which da is a section and 2a the apex angle. This
third curve is then 2ttB (a) sin a cos a, which by the above equa-
tion is equal to dF/Cda or the concentration of the emitted light
divided by the flux density of the incident light.
376 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
In case the scatter is in one direction only, as is the case with
ribbed glass for example, the integration is carried out directly
in the plane angle without recourse to the solid angle. When
the reflected or transmitted light is symmetrical about neither
the axis nor a plane, integration is rarely required in practise.
Distribution curves may, of course, be determined at any orienta-
tion of the sample and mean reflecting power found with the
ring reflectometer. Should further data be required, the distri-
bution curves for different orientations may be summed by plane
angles.
Fig. 2.— Brightness and angular radiation.
The graphical integration of the brightness curve by this proc-
ess is perfectly general, applying to even specular reflection and
transmission. Reflecting power or transmission coefficient at a
particular angle is a meaningless term but mean reflecting power
and mean transmission are perfectly definite quantities. The in-
tegration of both the reflected and transmitted light gives the ab-
sorption with quite satisfactory precision by this method. Total
reflection and transmission require further integration for ex-
tended sources.
Extended Sources. — Having obtained the distribution curve for
normal illumination (source of small angular extention), the
distribution curve for a more extended source of known bright-
ness is easily calculated. If the brightness of the source in the
direction of the sample is Bs lamberts, then unit area of the
latter receives Bslir light units per unit area from each unit area
of the source. Hence the distribution curve for the extended
OPTICAL PROPERTIES OF DIFFUSING MEDIA
377
source is the sum of distribution curves for the elements of the
source.
When the source is so large as to extend quite an angle from
the normal to the specimen and that is not highly diffusing, or in
case the specimen reflects unequally in different directions (ribbed
glass and textiles with a nap are examples) then several distri-
bution curves must be determined by observation. Data on a
few such cases will be given in the following report. In Fig. 3
are shown for illustration, curves obtained on glossy paper with
Fig. 3. — Distribution curves with extended sources.
wider and wider sources.
Letts Systems. — The intensity and distribution of light in image
forming optical instruments is of importance in many practical
problems. There are two principal cases to be considered (1)
object self-luminous or illuminated from in front and (2) object
illuminated from the rear by a condenser system, an image of the
light source being formed at the projecting lens.
Fig. 4. — Direct and projected images.
In the first case the object has a certain brightness in the
direction of the first lens. The light flux is constant through all
the series of zone pencils through the system except for light
losses in the lenses themselves. The same is true of the field
pencils. Hence the relative flux density in image and object is
378 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
the percentage transmission of the system times the solid angle
of the final zone pencil. The brightness of the image on the other
hand is the brightness of the object, as viewed from the first lens,
times the percentage transmission of the system.
In the second case the brightness of object is its transmission
coefficient times the flux per unit area and this latter is the angular
flux density divided by the square of the distance from the
source to the Gauss point of the condenser (roughly the focal
length of the condenser). Given the brightness of object found
in this manner, the brightness of the image and the flux density in
the plane of the image are found as in case one.
Nelson M. Black,
J. R. Cravath,
F. H. Gilpin,
M. Luckiesh,
F. K. RichtmyEr,
F. A. Vaughn,
P. G. Nutting, Chairman.
DIFFUSING MEDIA 379
DIFFUSING MEDIA III. PAPERS AND INKS.*
Synopsis: This report covers print papers; mat, semi-glossy, glossy;
sizings, fillers, inks ; writing papers and inks ; typewriter papers, inks and
carbons ; drawing papers and inks ; tracing papers and cloths ; blue print
papers ; photostat papers. Data are given for specular and diffuse reflect-
ing power and brightness, diffuse transmission and opacity, contrast ratio,
back reflection, entrant and exit scatter and other properties.
Print Papers and Inks. — The untinted print papers differ
chiefly in reflecting power (whiteness) and gloss. The reflecting
powers of the newspaper papers, unfilled and not very opaque,
run as low as 50 per cent.; medium grade papers, just perceptibly
grayish, reflect 60 to 70 per cent., while the whitest, finest
grade papers reflect as high as 83 per cent. Thin papers of low
opacity often reflect much less than 50 per cent.
The proportion of light specularly reflected varies from prac-
tically nothing up to 5 per cent, in the case of the highly glazed
plate papers. There is a wide variety of half gloss papers.
When the surface is dulled by putting a thin mat overcoat on a
glossy paper, the specular angle is small and the paper has a
subdued brilliancy and gives but slight glare. On the other hand,
paper that is heavily filled and calendered but unglazed has a
wavy surface that gives a bad glare on account of the wider
angle of specular reflection.
Print inks vary from dead mat to very glossy. The mat inks
vary in reflecting power from 3 to 4 per cent. The glossy inks,
if coated on a smooth hard surface reflect about 3 per cent,
specularly and 0.8 diffusely. If used on a rough or strongly
absorbent paper, they reflect more diffusely and may even appear
quite mat. The glare from glossy ink is particularly objection-
able in the larger cuts usually printed on glossy plate papers.
Typical distribution curves for the various classes of print
papers are shown in Fig. 1. Curve No. 1 is from a mat paper1
of 63.6 per cent, reflecting power ; No. 2, an unglazed book paper
of good quality; No. 3, a heavily calendered glazed paper, while
No. 4 is a glossy plate paper. These curves are taken with a
* Report No. 4 of the I. E. S. Committee on Glare.
1 Warren's cameo, paper.
380 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
disk source subtending a solid angle of 0.01 and perpendicular
illumination.
10 0 10 20 30
Fig. 1. — Distribution curves of print papers.
Total reflect-
ing power
No. I. Mat 0.636
No. 2. Slightly glossy • 0.575
No. 3. Semi-glossy 0.633
No. 4. Glossy 0.636
Specular
reflection
0.002 Warren "Cameo"
0.016 Jour. Wash. Acad.
0.031 Warren "Cumberland"
0.037 Kodak park plate.
In the figure only the portion of the distribution curves near
the specular angle are given. The reflecting powers given are
integrals of the distribution curves obtained as outlined in
Report No. 3. The specular reflection given in the table above
was obtained by integrating the excess over a smoothed cosine
curve.
In the table below are listed optical data on a number of print
papers ranging from newspaper to the heaviest plate papers. These
data are given by way of illustration of the desirable properties
and as means of drawing comparisons between papers more or less
familiar to all readers. They were taken with a spectrometer
with brightness photometer attachment.
From the reader's point of view, print paper should possess a
high reflecting power and but little gloss and the print or cuts on
the back should not show through. In the first column marked
R,f is given the diffuse reflecting power oi a single thickness of the
paper; in the following column (Rqq ) that of a pile of the paper
DIFFUSING MEDIA 381
so thick that adding more would not increase the reflecting power
of the first surface. These reflecting powers determine the
brightness when illuminated with a given source. In the third
column Rj is given the specular reflecting power, in column G
following the gloss or ratio of specular to diffuse brightness with
a normal illumination subtending 0.01 steradian (10 cm. square
at 1 meter).
Paper Rrf R^ R; G t T B D Di
Weather Review 055 0.63 0.000 0.02 0.109 0.178 0.0143 °-4°5 3-72
Science Abstracts 0.58 0.616 0.000 0.01 0.091 0.171 0.0120 0.394 4.32
Science 0.62 0.640 0.001 0.03 0.118 o.m 0.0047 °-523 4-44
Analen der Physik .. 0.540 0.600 0.008 0.47 0.063 0.223 0.0023 °-328 5.21
SitzungsberichteYVien 0.35 0.57 0.002 0.21 0.038 0.405 0.1070 0.208 5.47
(index)
SitzungsberichteWien 0.55 0.59 0.005 °-3° 0.061 0.194 0.0170 0.353 5.78
(text)
Industrial Arts Index 0.533 0566 0.003 0.15 0.53 0.24 0.027 0.290 5.48
"Light," 111. Eng.
Soc. 0.62 0.633 0.001 0.04 0.128 0.067 0.0017 0.760 5.65
Brittanica, India
Paper 0.59 0.62 0.000 0.02 0.048 0.215 0.019 0.280 5.82
Bible Paper 0.575 °-6i 0.000 0.02 0.048 0.21 0.187 °-3°5 6.34
Astrophysical Jour. . . 0.605 0.617 0.009 °-44 0.112 0.07 0.002 0.750 6.70
Rochester Herald 0.50 0.51 0.001 0.06 0.09 0.116 0.0067 0.644 7.14
Shap Shots 0.580 0.60 0.02 1.80 0.083 0.096 0.0039 0.628 7.56
Amer. Machinist 0.577 0585 0.019 °-9& °-I25 °-°5 o.oon 0.956 7.65
(cov. )
Amer. Machinist 0.550 0.57 0.019 IO° 0.078 o. 10 0.0045 0.670 8.58
(text)
Photographic Jour. .. 0.57 0.5S3 0.013 o-11 °°95 0.081 0.0028 0.729 7.67
"Cumberland" (War-
ren) 0.595 0.598 0.03 1.26 0.117 0.046 0.0009 0.946 8.08
Inland Printer (text) 0.60 0.625 0.021 1. 12 0.083 0.0S1 0.0026 0.680 8.18
Inland Printer (plate) 0.58 0.50 0.023 I22 0.119 0.042 0.007 0.988 8.30
E. K. Co. Bulletin ... 0.590 0.60 0.037 1.89 0.123 0.038 00006 1.032 8.38
Jour. Wash. Acad. Sci. 0.57 0.50 0.016 0.50 0.088 0.75 0.0024 °-752 8.55
Moving Picture World 0.555 °-565 0.015 °-78 0.073 0.113 0.0059 0.602 8.25
Modern Sanitation... 0.59 0.595 0037 1.89 0.101 0.056 0.0013 0.870 8.60
Central Zeitung 0.55 0.60 0.006 0.38 0.053 °-I7 o-OI3 0.414 7.80
Engineering World-. 0.575 °-592 0.01 0.52 0.074 0.115 0.0056 0.668 9.00
The thickness of the samples is given in column t in fractions
of a millimeter, the percentage transmission in column T. Most
papers absorb from 75 to 95 per cent, of the incident light not
reflected, i — T being the absorption. Column B is T2(i — R).
Of the incident light, the fraction R is reflected and 1 — R enters
5
382 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
the paper, T(i — R) reaches the back face. If a similar sheet
underlies the first TR(i — R) re-enters the back of the first
sheet and T2R(i — R) emerges from its front face (see report
Diffusing Media I). The brightness of the front face depends
upon the sum of the light reflected from this face and the light
reflected back from underlying sheets or R-f-T2R(i — R).
Hence if T2 is small and R is large, 1 -\- B is the relative bright-
ness of plain paper and paper inked on the back. If B, the back
reflection, is greater than half a per cent. (0.005), print on the
back will show through quite perceptibly. No paper should be
used except for special purposes for which B is greater than
0.02, if B is 1 per cent. (0.01) the transparency is annoying.
Density D = — log T, in the next column, is a quantity pro-
portional to the thickness and a proper measure of the opacity
of a paper. Dx = ( — log T)/t, the specific density or the density
per unit thickness, is a measure of the quality of the paper mate-
rial. It depends largely upon the quality and the amount of filler
used.
Reflecting powers range from about 50 per cent, for the news-
papers up to nearly 70 for Nos. 4, 7, 8 and 16. These are
slightly cream tinted papers; No. 6 is by far the whitest paper
of any but has a lower reflecting power probably on account of
blue used to counteract a slight yellow. The back reflections
vary from practically nothing (20) up to 0.12 1 in No. 5, a very
thin transparent paper. Specific densities range from 3.7 up to
a fairly definite maximum at from 8.5 to 9.0.
Fillers. — Fillers are used to give the paper opacity as well as
to give it certain mechanical properties. Good filler should then
possess high specific density and high reflecting power. Kaolin
is largely used for the cheaper and medium grade paper, baryta
for the most expensive papers. Both reflecting power and opacity
increase with dryness and with increasing fineness of particle2
until the particle is smaller than a light wave. The ideal filler
would be a mass of non-hygroscopic transparent crystals about
0.0002 mm. in mean diameter and free from smaller and larger
particles since these would tend to lower both opacity and reflect-
ing power.
2 Trans. I. E. S., 1914, p. 593.
DIFFUSING MEDIA 383
The reflecting powers of fillers vary from 60 per cent, or lower
up to over 80 per cent. Their specific densities are approxi-
mately: kaolin, dry powder, 1.96; magnesium carbonate block
0.35, powder, 0.61 ; barium sulphate powder, 2.30.
G laces. — The glazing material chiefly used is an inferior grade
of gelatine with a refractive index of about 1.36 and a specular
reflecting power of 2^2 per cent. Any glazing is entirely dele-
terious optically, but it is considered necessary in some forms of
paper to give a smoother surface and to prevent too free pene-
tration of the ink.
Inks. — Print inks differ in specular and diffuse reflecting
power. All are so opaque that the twice transmitted light reflected
from the underlying paper is quite negligible wherever the ink
actually covers the paper. Glossy inks are preferred for their
somewhat better working qualities. Optically, the glossy inks
have lower diffuse reflecting powers than the mat inks, hence are
blacker and present a greater contrast with the paper. The mat
inks are preferable only in the complete absence of glare. The
following data indicate the properties of some characteristic
printing materials.
1. Ord. print paper and ink- •
2. Jour. Am. Soc. Mech. Eng.
3. Snap shots
4. Calender 0.59
5. " Light," its use and misuse 0.65
The relative transmission, fourth column, is the ratio of the
light transmitted through paper and printed character to the
light through the paper alone. The density of ink, fifth column,
is the negative logarithm of this ratio. The density per milli-
meter (specific density) of print inks are too high to measure
with any precision (about 60) and of little interest. The back
reflection, last column, is the relative brightness of paper alone
and paper printed on the back, the quantity computed in the
table on print papers, above, plus unity.
The specular reflection of an ink depends upon the matness of
the paper upon which it is printed. The following measurements
were taken using a glossy ordinary ink and a mat ink each on
Diffuse ref.
power
Rel.
trans.
Dens,
of ink
Back
reflec-
tion
Paper
Ink
Contrast
0.59
O.025
23.6
0.03
1-52
I 05
O.61
O.043
14.2
O.13
O.89
I.03
0.63
0.047
14.O
O.I2
O.92
I.02
0.59
O.030
I9.8
O.04
I.40
I.08
O.65
0.037
17-5
O.IO
I. OO
I. OO
384 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
three supports; photographic film, a glossy plate paper and a
mat paper.
Reflecting power
Diffuse Specular Gloss
Glossy ink on film 0.008 0.034 430
Glossy ink on glossy paper 0.008 0.017 2I°
Glossy ink on mat paper 0.012 0.006 51
Mat ink on film 0.036 0.0024 2-9
Mat ink on glossy paper 0.036 0.0020 2.4
Mat ink on mat paper 0.037 0.0015 2.2
Specular reflection from ink is unobjectionable when below half
a per cent. (0.005) and even glossy ink on a mat paper, not too
fine grained, will not give serious glare. The glossy ink of the
above table is seen to be about four times as black as the mat;
that is, the diffuse reflecting power is only a quarter of that of
the mat ink.
Writing Papers and Inks. — Writing papers differ from print
papers as a class chiefly in the glaze applied to render it non-
absorbent and prevent running of the ink. This glazing material
(gelatin, dextrin, glue, resin or soap) being of low index (1.36
about) and transparent, has the effect of (a) slightly lowering
diffuse reflecting power and (b) considerably increasing specular
reflecting power. In other words, it tends to render the paper
slightly grayer and much more glossy. Many writing papers,
however, have so low a gloss as to be quite unobjectionable.
The data given below is of the same nature as that given above
for print paper and is to be interpreted in the same way.
Kd Roo Ry G t T B D Dj
Linen finish ordinary 0.61 0.64 0.0030 0.21 0.13 0.127 0.006 0.48 3.71
Commercial ordinary 0.57 0.63 0.0024 OI7 °-°7 o-^S 0.013 °-4° 5-72
Writing ink was tested when on a semi-glossy paper and when
on a specular film support. The inks were a good ordinary pen ink
(Buffalo Standard) and a carbon (Higgin's "Eternal Black").
Rrf R5 T D
Ordinary iron ink on film 0.025 0.005 0.019-0. 18 0.74-1.74
Ordinary iron ink on glossy paper . 0.035 0.0000
Ordinary iron ink on mat paper . . . 0.054 0.0001
Carbon writing ink on film 0.005 0.085 0.096-0.44 0.35-1.58
Carbon writing ink on glossy paper 0.027 0.004
Carbon writing ink on mat paper.. 0.045 0.0012
DIFFUSING MEDIA 385
Typewriter papers, inks and carbons. Typewriter papers are
quite similar to the print papers of medium grade with but little
fillers and very little glazing.
Rd rot R* G < T B D D,
Ordinary E. K. Co. 0.515 0.594 0.0006 0.05 o. 10 0.180 0.015 0.432 4.32
Ordinary I. E. S. •• 0.50 0.565 0.0000 0.00 0.87 0.216 0.023 °-2^2> 4-2°
Tissue carbon paper 0.36 0.552 o 005 0.64 0.038 0.366 0.085 °-243 6.38
The ink impressions vary greatly in density. The data given
below refer to what was considered a fair average density.
Rd Ry G T D
Ordinary black ribbon ink 0.05 0.000 0.07 0.37 0.43
Ordinary blue ribbon ink 0.128 0.001 0.37 0.62 0.21
Ordinary red ribbon ink 0.160 0.002 0.25 0.55 0.26
Carbon paper 0.032 0.005 0.25 0.24 0.62
Drafting Paper and Ink. — Drafting paper contains somewhat
more filler and sizing than print paper and less than writing
paper. The data below refer to a good ordinary paper and to
some of special quality.
Rs Roo Ry G t T B D D!
Good ordinary . 0.54 0.64 0.0005 °-°4 0.117 0.222 0.023 0.3182 2.72
Special quality 0.62 0.64 0.0012 0.09 0.19 0.078 0.002 0.684 3-6o
The India ink which the following data applies is of the or-
dinary prepared variety (Higgins).
Rd Rs G T D
India drafting ink on film. . . 0.013 °-°37 2&4 0.017-0.47 0.33-1.82
India drafting ink on paper • 0.029 0.002 5.3
Tracing Cloth and Paper. — The most important optical prop-
erty of tracing cloth is its transparency. Glare and reflecting
power are of less consequence. The requirements are quite sim-
ilar to those for window envelopes (Report 6) and the reverse
of those for print paper. With tracing cloth, the most distinct
possible view of the underlying layer is desired. The same high
transparency is desired for printing. The necessary fabric used
as a body, however, scatters light to a considerable degree. Trac-
ing paper must be opaque enough to show well a drawing made
upon it but so thin and transparent that prints may be made
directly through it.
Different grades of tracing paper and cloth differ widely in
386 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
properties. Below are given distribution data on materials of
about an average grade.
Relative Brightness.
o° 5° io° 150 300 450
Tracing cloth, reflection 0.41 0.37 0.34 0.32 0.28 0.28
Tracing paper, reflection 0.77 — — — — 75
1800 175 170 165 150 1350
Tracing cloth, transmission. . . 6.3 5.3 3.6 2.1 0.82 0.53
Tracing paper, transmission • . 0.87 — 0.76 0.69 0.57 0.4b
These readings were taken with an illumination and a
photometer scale such that the reading on a 100 per cent, per-
fectly diffuse reflector would have been 1.56.
With the same constant (1.56) the following data on a number
of tracing cloths were obained.
Cloths over black R Over
, --' > White Contrast B 45 B 135
BO° B 45 B 135 B 180 B 45 Ratio BO B 180
15817 0.78 0.39 0.41 3.7 0.79 0.49 0.50 O.II
P. 13 O.72 O.41 O.42 2.03 O.75 O.54 O.56 0.2I
N. T. 7 0.88 0.38 0.60 3.3 0.78 0.47 0.43 0.18
15742 I.04 O.40 O.56 2.0 O.80 O.50 O.39 O.38
12 O.72 O.44 O.46 2.4 O.Sl O.54 O.61 0.I9
S3 O.75 O.42 O.45 I.32 O.79 O.54 O.56 O.34
Vi 0.55 0.29 0.41 2.00 0.74 0,52 0.71 0.21
E. K. 0.51 0.24 0.41 5.0 0.74 0.33 0.48 0.08
The first four column give the observed brightness at the angles
°> 45> J35 aild 1800 from the (perpendicular) direction of illum-
ination in a black walled room giving very little stray light. "B
45 over White" is the brightness of the cloth when backed by
drafting paper of 64 per cent, reflecting power. The contrast
ratio is the ratio of brightness over white to brightness over
black. B45 : Bo is entrant scatter, B135 : B180 exit scatter.
(See report No. 2.)
Blue print paper is of medium reflecting power and weight,
mat and very absorbent. The equivalent density of the photo-
graphic deposit as compared with inks is of interest. The follow-
ing data were taken on two samples, one of the very high grade,
the other of inferior quality.
Rrf Rs B:W T D^
High grade, white 0.58 0.0005 0.16 0.31
High grade, blue 0.084 0.0004 0.088 0.56
Low grade, white 0.44 0.0010 0.13 0.35
Low grade, blue 0.07 0.0009 0.106 0.51
DIFFUSING MEDIA 387
The reflecting powers of the exposed (blue) parts run about
7 or 8 per cent., only about twice that of mat print ink. The
maximum blacks of the regular photographic papers run from
(glossy solio) 0.6 per cent, up to the 4 per cent, on the mat
papers.
Photostat paper is a thin, inexpensive photographic paper.
Data on two samples are given. These did not differ greatly in
material but the "special" had been forced by a professional
photographer to give maximum contrast.
Rrf R5 B/W T T)b
Ordinary white (clean) 0.594 0.0014 0.26
Ordinary black (exposed) 0.056 0.0004 0.094 0.056 0.68
Special white (clean) 0.594 0.0012 0.33
Special black (exposed) 0.03 0.0003 0.51 0.03 0.85
The blacks are nearly as black as print ink while the contrast
ratio of black to white runs as high as 20 for the carefully devel-
oped sample.
The following report is to deal with the regular photographic
papers.
Nelson M. Black,
J. R. Cravath,
F. H. Gilpin,
M. Luckiesh,
F. K. Richtmyer,
F. A. Vaughn,
P. G. Nutting, Chairman.
388 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
DIFFUSING MEDIA IV.— THE OPTICAL PROPERTIES
OF PHOTOGRAPHIC PAPERS.*
Synopsis: Photographic papers vary in reflecting power from pure
white to dense black and in gloss from a nearly pure mat to a high gloss.
Practical methods of measuring and specifying reflection densities and
sensitometric data are outlined, distribution analyses of various types are
given, gloss and its determination are discussed, data are given on trans-
mission densities and diffusion in photographic plates and negatives.
Aside from the fact that nearly every one is more or less of a
photographer and interested in photographic prints, the investi-
gation of the optical properties of photographic papers is of great
interest because in this product is prepared a wide range of pre-
cisely reproducible gloss and because in each paper with its
particular gloss, a wide range of diffuse reflecting powers may be
produced by the photographic process. No other product offers
such excellent material for the study of these two optical prop-
erties.
REFLECTING POWER.
Photographic papers unexposed or fixed without exposure
reflect from 65 to 75 per cent, and this, of course, represents the
lightest high lights possible in a print. A print reflecting but 50
per cent, is just noticeably grayish, 30 per cent, a medium gray,
3 to 8 per cent, a muddy black. The maximum blacks obtainable
on any papers reflect diffusely less than 1 per cent. — just about
as much as the blackest printer's ink.
In viewing a photographic print it is usually held nearly per-
pendicular to the line of sight. The practical measurement of
reflecting power involves illumination at an angle of 45 ° and an
observation of brightness in the direction normal to the surface.
A print may be comfortably viewed under widely different angles
of illumination, but 45 ° is considered a fair average direction for
testing purposes. The photometer for small areas described by
Jones and Nutting1 measures reflecting power in this manner.
This photometer has been used chiefly for testing photographic
papers, in fact.
A set of readings of diffuse reflecting power taken on un-
* Report No. 5, I. E. S., Committee on Glare, 1914-15.
1 Trans. I. E. S., p. 611. vol. IX, (1914).
DIFFUSING MEDIA 389
exposed and fully exposed papers is given below together with the
maximum contrast ratio. The readings are relative to the read-
ing on a perfectly diffusing surface of 109- per cent, reflecting
power under the same illumination.
Max. white Max. black Max. contrast
Azo A (Mat) 0715 0.038 19
C (Glossy) 0.745 0.018 41
D (Semi-gloss) 0.65 0.029 22
E (Velvet) 0.70 0.023 30
F (Glossy) 0.70 0.013 54
G (Mat) 0.695 0.040 17
Glossy velox (reg.) 0.70 0.010 70
Solio 0.64 0.006 107
The maximum blacks are of about the same reflecting power
as printer's ink (Report No. 4). It is interesting to note that
while the whiteness appears to bear no relation to gloss, the
maximum blacks are always deeper in the glossy than on the
mat papers. Ordinary glossy printer's ink reflects (1. c.) less
than a third as much diffusely as mat ink — 3.6 against 0.8 per
cent. The range is somewhat less than in the papers listed above,
namely, 4.0 to 0.6 per cent.
The fact that the deeper blacks are obtained on the glossy
papers and inks is possibly due to the fact that the light absorbing
particles are covered with a coating of more or less transparent
substance of about the same refractive index as themselves, hence
there is little reflection at the interface. With mat surfaces, the
absorption within the particles is of the same order but the sur-
face reflection from the individual particles is so great that con-
siderable light is scattered.
In a series of grays running from white to black made on
photographic paper, the specular reflecting power remains con-
stant or nearly constant while the diffuse varies by a factor of
20 to 100. Gloss then varies through the same range of values,
gloss being defined as the ratio of specular to diffuse brightness.
In the sensitometry of photographic paper it is the diffuse re-
flecting power that is taken as a measure of the photographic
effect. A series of about 20 exposures are made, each the square
root of two times the preceding, by printing through carefully
selected neutral gray film of the proper series of densities. After
development the reflecting powers of the exposed spots are
390 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
measured relative to the adjacent white paper, the paper being
illuminated at an angle of 45 ° and read perpendicularly. Re-
flection densities are taken as the common logarithm of relative
reflecting power. This is not proportional to the mass of reduced
silver as is the case with transmission densities (-log transmis-
sions) except at the lowest densities. Specular reflection is ig-
nored as it does not affect either relative exposure nor the deposit
of silver. A typical series is given below. It is a test of the
paper known as Artura Iris A. T is the transmission of the
series of printing screens, D* (= — log T) the corresponding
printing densities (steps roughly 0.15), E the relative exposures,
R<f the relative reflecting power of the print spots and white field
adjacent, and Dr the reflection densities of the series.
Step
T
»p
E
Rrf
Dr
I
0.0025
2.709
I.O
1.0
0.0
2
0.0029
2.551
I.I6
1.0
0.0
3
O.OO45
2.385
I.80
1.0
0.0
4
O.OO54
2.268
2.l6
1.0
0.0
5
0.0077
2.127
3.08
1.0
0.0
6
0.0II2
1-939
4.48
1.0
0.0
7
O.OI57
1.803
6.28
0.97
0.015
8
0.0240
1.643
9.60
0.86
0.065
9
O.O308
1.510
12.32
0.75
0.125
10
O.O452
1-345
18.08
0.48
0.32
11
O.O434
1.364
17.36
0.565
0.25
12
0.0622
1.206
24.88
0-354
0.46
13
0.0912
1.040
36.48
0.220
0.66
14
0.1205
0.922
48.2
0.164
0.78
15
0.165
0.782
66.0
0.1 1 1
0.97
16
0.255
0-594
102.0
0.055
1.26
17
0-347
0.462
138.8
0.041
1.38
18
0.503
0.298
201.2
0.039
1.41
19
O.684
0.165
273.6
0.038
1.42
20
1.0
0.0
400.0
0.038
1.42
The sensitometer curve is D,- plotted as a function of log E.
From this, speed, gradation and maximum gradient are read off.
GLOSS AND GLARE.
The distribution of the light reflected from four selected pho-
tographic papers is shown in Fig. 1 to illustrate the character and
range of diffusion provided for. Curves were taken with illum-
ination nearly normal and 0.01 in angle. The curve for Azo C is
DIFFUSING MEDIA
391
plotted with half the ordinate scale of the others. The range in
gloss is from an almost dead mat surface (G) to the extremely
glossy C. Solio, regular glossy Velox and Azo F are of the same
type as C but slightly more glossy. The specular projections on
the curves for C and D are of the ordinary type such as is pro-
duced by varnish or by the calendering of print paper. E, how-
ever, shows the superposition of two distinctly different types of
gloss, one of the ordinary type and the other of about three times
the angle but of less maximum reflecting power.
amci.es onuriicTioH
Fig. 1.— Distribution Curves of Azo C, D, E and G.
\ iewed at the specular angle under a single bare lamp or other
narrow angle illuminant, papers C and D show a small glare spot
of about the same size but C brighter than D, while E shows a
much larger spot. It is desirable to distinguish between the
effects of (a) the maximum height of the distribution curve (b)
the width and (c) the area of the projecting part of the curve
representing specular reflection. The maximum height depends
upon the brightness of the illuminating source, the width upon
39-2 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
the angular width of the source and the area upon both. Now,
gloss defined as the ratio of specular to diffuse brightness, is a
measure of height and is independent of width or area of distri-
bution curve. On the other hand, total specular reflection, the
area of the projecting area on the corrected distribution curve, is
not a measure of either gloss or glare. For practical purposes
it might be desirable in some cases to record the angular spread of
light in the glare spot when a narrow source is used, but usually
gloss is of chief or sole value in photographic papers. In diffus-
ing globes it is the maximum spread that is particularly desired.
PHOTOGRAPHIC PLATES AND NEGATIVES.
Undeveloped photographic plates have a high turbidity and for
blue light a high opacity. The emulsion with which the plate is
coated is a yellowish white in color and roughly 0.02 mm. thick.
It has a moderate surface gloss. Distribution curves plotted for
Seed 23, 30 and lantern plates with white light gave substantially
the same results. The brightness given is relative to that of a
perfectly diffusing surface reflecting 100 per cent.
Reflection Transmission
Angle 15 30 45 60 75 105 120 135 150 165
Brightness... 0.69 0.56 0.54 0.52 0.42 0.27 0.33 0.35 0.37 0.37
There is no specular transmission but a specular reflection of
about 5 per cent. The density is about 0.2 in the yellow and very
high in the blue, the density per millimeter is about 10 in the
yellow.
In photographic negatives the absorbing silver grains are in
the form of spongy black masses imbedded in transparent gela-
tine. A great deal of light is scattered in addition to that directly
absorbed. Diffuse transmission is several times greater than
specular. Diffuse densities deterrhine exposures in contact prints,
specular densities in projection printing and enlarging. Different
plates differ in ratio of diffuse to specular densities. Different
exposures on the same plate show the same relative densities in
some plates and different in others, the variation being most
marked in the coarse grained high speed plates.
DIFFUSING MEDIA 393
Diffuse Specular PJ
Plate density density Hd R 45°
Seed lantern 0.47 0.77 1.64 0.050
1.04 1.66 1.60 0.023
1.69 2.67 1.57 0.022
2.75 4.3 1. 6 1 0.021
Seed 23 0.75 I-I3 1-5* °-°3i
1.68 2.51 1.49 0.021
2.90 4.3 1.50 0.021
Seed 30 0.50 0.89 1.78 0.052
1. 12 1.85 1.65 0.025
1.88 2.83 1.5 1 0.022
Seed graflex 0.55 1.17 2.18 0.051
1.22 2.27 1.86 0.028
1.78 3.12 1.67 0.028
Cine pos. film 0.06-2.11 0.10-3.30 1.58 (mean) —
The reflected and transmitted light is not uniformly distributed.
The following data taken on a medium exposure on Seed 23 is
typical :
Angle 15 30 45 60 75 105 120 135 150 165
Rel. brightness 1.7 0.60 0.39 0.32 0.26 0.079 0.128 0.25 0.50 1.96
The sensitometry of plates by the Hurter and Driffield method
is described in treatises on photography and applied optics.
Considerable data of related interest on the specular and diffuse
reflecting powers of ordinary papers is contained in our report
No. 4 on papers. General relations and definitions are given in
our general report, No. 1, and in report No. 2 on diffusing media.
Nelson M. Black,
J. R. Cravath,
F. H. Gilpin,
M. Luckiesh,
F. K. Richtmyer,
F. A. Vaughn,
P. G. Nutting, Chairman,
394 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
WINDOW ENVELOPES.*
At the request of a letter carriers' association the Committee
on Glare of the Illuminating Engineering Society has undertaken
an investigation of the optical properties of the various kinds of
window envelopes now in use. About ioo samples of used
envelopes were submitted by the letter carriers' association for
the tests. The determinations were made in a well equipped
optical laboratory under the personal supervision of the Chair-
man of the Glare Committee on about 25 carefully selected
samples. A classification of material, the conclusions drawn and
the more important data obtained are given below :
In the window envelopes in question the windows are of the
following four classes :
1. An oblong hole without any covering.
2. A window covered by an insertion of clear, transpar-
ent film usually of gelatin.
3. A window covered by a translucent insertion of special
oiled paper.
4. The window is merely an oiled or varnished portion of
the envelope itself. The envelope is frequently of
heavy blue or yellow paper.
The essential properties of these four forms of windows are
those outlined below:
1. The open window is visually equivalent, except for a slight
bordering shadow, to viewing the address directly. The slight
bordering shadow occurring sometimes under poor illumination
has no ill effect of any consequence on vision.
2. The window of clear film causes :
(a) A general lowering of brightness of the address by about
10 per cent. This is equivalent merely to a lowering of illum-
ination by that amount for any angle of view except the angle
of specular reflection.
(b) Occasional specular glare, very bright except for very
diffuse indirect lighting. This glare spot is about one-hundredth to
one-tenth as bright as the source of light whose image is re-
flected. It is very bright indeed when bare lamps are used as il-
* Report No. 6 of the Committee on Glare of the Illuminating Engineering Society.
WINDOW ENVELOPES 395
luminants. The diffuse brightness of the address read is de-
termined simply by the illumination at that point and the diffuse
reflecting power of the paper, and is thus very nearly independent
of diffuseness of the illumination and the angle of view.
(c) Clear windows produce no noticeable decrease in con-
trast or in definition except at the angle of glare.
3 and 4. Windows of translucent materials cause :
(a) A slight general lowering of brightness due to loss of
light by specular reflection from their surfaces of the same order
as that caused by clear windows. (See 2a.)
(b) A specular glare similar to 2b.
(c) A veiling effect (superposed brightness) due to light dif-
fusely reflected from the material of the window. This causes
a serious lowering of contrast to about 1/10 its value in the un-
covered address (see data below).
(d) A veiling due to diffuse transmission through the win-
dow. This causes at best a serious loss of definition rendering
the address quite illegible in the worst cases even under good
illumination and with the window pressed close to the address.
We have made the following measurements on selected samples
of the various classes of window envelopes. A strip of mat
black paper was placed on mat white paper (except in tests
Nos. 3 and 8) and the reflecting power of each determined be-
hind each window :
Reflecting power
White Black Contrast
per cent. per cent. ratio
Test No. i. Bare test pieces 68.0 2.1 32.4
2. Clear gelatine window 61.3 2.8 22.0
3. Ditto, ink on brown paper . . . 43.0 18.0 2.4
4. Oiled tissue paper (class 3) •• • 61.0 15.0 4.1
5. Ditto, another sample 61.0 11. 5 5.3
6. Envelope, oiled(white, class 4) 49.0 14.0 3.5
7. Ditto, blue envelope 35.0 9.0 3.9
8. Ditto, ink on bluish paper •• • 18.5 9.0 2.1
It is to be noted that the oiled and varnished paper windows
increased the apparent brightness of the black strip from 5 to 9
times and decreased the contrast by from 8 to 10 times.
The diffusing properties of these window materials were
further determined by the ordinary methods. Each sample is
396 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
illuminated perpendicularly by a collimated beam of light. Then
its brightness is measured at angles of 45, 135 and 1800 from
the incident beam. The unit of brightness is that of a diffuse
reflector reflecting 100 per cent., magnesium carbonate reflecting
88.0 per cent.
Material Rel bright-
ness at 450
Oiled tissue (c. f. No. 4) 0.45
Oiled env. white (No. 6) 0.52
Ditto, blue (No. 7) 0.12
The specular transmission of each sample was zero. No light
was transmitted directly through. The scatter is from ]/% to y2
as much as is caused by a perfectly diffusing surface.
Nelson M. Black,
J. R. Cravat h,
F. H. Gilpin,
M. Luckiesh,
F. K. RlCHTMYER,
F. A. Vaughn,
P. G. Nutting, Chairman.
135°
1800
B45
Bi35
Bi35
B180
O.62
165
0.73
O.OO26
O.74
38
O.70
O.OO51
O.40
6l
0.30
O.OOI5
DIFFUSING MEDIA 397
DIFFUSING MEDIA VI.— INTERIOR FURNISHINGS.*
Synopsis: In this report are discussed the optical properties of walls,
woodwork, ceilings, floors, fixtures, shades, draperies and furniture as
dependent upon the raw material, the finish and the covering. Attention
is given largely to the general properties necessary to minimize glare con-
sistently with good illumination. The relation of illumination to the
properties of furnishings is considered in each case.
The proper choice of surfaces for house and office furnishings
to provide a maximum of eye comfort involves not only the sur-
faces themselves but their positions relative to illuminant and
inhabitant and the character of the illuminant. The condition
desired is not necessarily the elimination of all glossy surfaces
but an arrangement such that no glossy surfaces are in a position
to cause objectionable glare. In other words, the desired condi-
tion is one of no glare rather than of no gloss. A gloss that
would be intolerable in a table top is of no consequence in a
baseboard, fireplace or ceiling, since from plane surfaces placed
as these are, under ordinary conditions, no specularly reflected
light can enter the eye.
Limits of tolerance are discussed in the general report (Report
No. 1) on classes of glare and means of suppression. The
classes of glare involved in houses and offices are :
(1) Brightness Glare. — Excessive brightness such as occurs
with sun shining directly on snow, white paper or a white window
shade. The limit of tolerance depends upon (a) the state of
brightness accommodation of the eye due to the general bright-
ness of the surroundings and (b) upon the angular area of
the bright surface viewed. Some measurements indicate that the
product of brightness and area, that is the total candlepower of the
bright object viewed, would be a better measure of brightness
glare than mere brightness alone. Possibly some simple function
of both brightness and area will ultimately be chosen as a measure
of this kind of glare.
(2) Contrast Glare. — Contiguous bright and dark objects
cause disturbance of vision if their relative brightness is exces-
* Report No. 7, I. E. S., Committee on Glare, 1914-15.
6
398 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
sive. A bright illuminant viewed against its background, a dark
window frame against sky or a bright landscape and a glare spot
on a glossy surface are familiar examples.
At moderate and high intensities a relative brightness of 100:1
or over is uncomfortable and is to be avoided. Ordinary print
on white paper presents a contrast of about 20:1. When the
darker part of the field of view is but little lighter than complete
darkness (a hole in a black lined box, say) then relative bright-
ness may be very high without producing an objectionable effect.
This begins when the brightness of the brighter area is over a
fixed value, considerably less than the limit in case the whole
visual field is bright (case 1 above) or is free from excessive
contrasts.
The limit of tolerance in contrast glare is somewhat lower the
shorter the line of contact between the neighboring surfaces show-
ing excessive contrast. In specifying contrast glare it is, of
course, total brightness (specular plus diffuse) which is to be
considered.
(3) Veiling Glare. — By veiling glare is meant that condition in
which the surface to be observed appears covered with a light
or dark veil of a different or imperceptible pattern. A picture or
polished wood viewed from near the specular angle, a landscape
viewed through a window screen or dirty window are familiar
examples. Bright veiling is measured by relative contrast ; that
is, by the ratio of contrast with veiling to contrast without veiling.
Walls and Wall Coverings. — Walls of rooms may vary widely
in reflecting power, hue, shade or gloss. A low diffuse reflecting
power means, of course, a dead loss in illumination, but white
walls highly illuminated lead to mild visual discomfort. Gloss in
the middle levels may lead to a highly objectionable glare, but
if near the floor margins or ceiling no specularly reflecting light
can reach the eye. With totally indirect illumination consider-
ably more gloss may be tolerated, since the light specularly re-
flected from glossy walls is reflected downward at a much larger
angle than under direct or semi-indirect illumination.
But little data on wall coverings of general value can be given
on account of their widely varying nature.
DIFFUSING MEDIA 399
Reflecting power
Diffuse Specular
Raw plaster 0.40-0.50 0.0
Finished plaster 0.60-0.70 0.005-0.020
Fine white washes 0.70-0.84 0.0
White tile, marble 0.50-0.70 0.0 -0.05
White paint 0.40-0.60 0.05
Finished wood — light 012 0.04
Finished wood — dark 0.06 0.04
Aside from esthetic considerations, perhaps the ideal wall cover-
ing from the standpoint of economy and eye comfort would be one
free from gloss throughout and varying in diffuse reflecting power
from 30 per cent, near the floor to 80 per cent, near the ceil-
ing. The high reflecting power above saves light and does not
greatly affect vision, the low reflecting power below avoids eye
fatigue. A reflecting power as low as 10 per cent, or less on the
lower part of a wall would not only waste light but be slightly
uncomfortable to an eye accommodated to the brightness of white
paper.
Ceilings. — That ceilings should be white and of high total re-
flecting power is widely recognized in practise. In all ordinary
cases the sole consideration is economy of light since they are
above the ordinary level of vision. In very large rooms a glossy
surface is to be avoided since in such cases troublesome glare
within the line of vision may occur. Diffuse reflecting powers of
70 to 80 per cent, are readily available in papers, washes and
paints.
Floors. — Floors are constantly within the range of vision and a
moderate to low reflecting power is preferable. Near the walls,
gloss on a floor is quite unobjectionable since no specularly re-
flected light can reach the eye. Near the center of the room
uncovered, glossy floors are intolerable. The common practise
of covering the centers of floors with rugs is an excellent one,
since rugs are usually very mat and of but moderate reflecting
power.
But little reflection data on floor materials, finishes or coverings
can be given on account of their variability. The following data
refer to oak of about an average tint:
Reflecting power
Red Green Blue White
Oak oiled diffuse 0.074 0.046 0.012 0.053
Oak oiled specular 0.036 0.042 0.032 0.039
400 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Maple has about the same reflecting power as oak, perhaps a little
higher on an average. A fresh surface on soft pine reflects 15
to 40 per cent., white tiling and marble reflect about 60 per cent.
Furniture and Fixtures. — In the finishing of furniture and
fixtures, common practise is bad, in that glossy surfaces and un-
comfortable glare are commonly met with. Varnished and
polished tables and chairs near the center of a room can hardly
fail to present bad glare spots to anyone in a room unless the
illumination be totally indirect and in this case much of the
beauty of the wood is lost in the overlying gray veil. Metal or
metal painted fixtures and gilded picture frames are quite as
bad, or worse, since their reflecting powers are higher than that of
varnish. A little dull finished furniture is on the market and it
is to be hoped that it will meet with increasing favor. Metal
coverings of low gloss are not common but could no doubt be
developed. The relative specular and diffuse reflecting powers
of metals run about as follows :
Reflecting- power
Diffuse Specular
Brass polished 0.018 0.46
Copper polished 0.03 0.21
Nickel polished 0.003 o. 70
Aluminum paint 0.29 0.22
The amount by which the reflecting powers of brass are spec-
trally selective is shown by the following table:
White Red Yellow Blue
Diffuse 0.018 0.017 0.023 0.014
Specular 0.46 0.45 0.45 0.39
The reflecting powers of finished mahogany surfaces average
about 4 per cent, diffuse and 5 per cent, specular. The diffusely
reflected light is practically all red, while the specular is non-
selective.
Window Shades, Curtains and Draperies. — The requirements
for window coverings are similar to those for wall coverings on
north exposures. Where exposed to direct sunlight only very
opaque shades, and curtains and draperies of very low reflect-
ing power should be used, otherwise they become at times in-
tense sources of light directly at the level of vision. A double
coated shade, black outside and of a color harmonious with the
prevailing tones of the room inside, is to be chosen.
DIFFUSING MEDIA 4OI
General Remarks on Furnishings. — Considered from the stand-
point of gloss and glare, ideal furnishings should show ( i ) a
general decrease in diffuse reflecting power from 80 per cent, on
the ceiling down to about 20 or 30 per cent, on the floor and (2)
no gloss anywhere except (if desired) above the eye level on the
ceiling and near the angle of floor and wall, a location from
which no glare, under ordinary conditions, can reach the eye.
Common practise is good in regard to the first of these condi-
tions but very bad in regard to the elimination of specular reflec-
tion. In dwellings there is wide latitude for improvement; in
auditoriums, stores, factories and machine shops conditions are
much more difficult to deal with, but general practise is better
developed.
Illuminants. — From the standpoint of glare alone, the rule to
be observed is to keep intense sources of light well above the
visual level. The fault commonly met with is not insufficient
light so much as improperly placed sources of light.
Artificial light sources are easily dealt with, thanks to the
variety of lighting units and fixtures available. The subject is
discussed at length in the illumination primer1 published by this
society. On the other hand, common practise in day illumination
is bad and the proper arrangement of window lighting quite dif-
ficult in most cases. Ordinary window lighting is bad, in that it
is largely at the level of vision and that it is surrounded by rela-
tively deep shadow. The remedy for these conditions would be
to cut off the light entirely at the level of vision and illuminate
the room solely by light from the upper part of the window.
However, the loss of view involved would hardly be tolerated.
The light from the sky quadrant available passing the upper sash
is easily thrown on the ceiling and used to illuminate the room
in an ideal manner by the use of an inclined mirror or a plain
white surface. To partly avoid excess illumination at eye level
without cutting off the view, a sill shade may be drawn up when
conditions are worst or the window may be supplied with yellow
or amber glass. This is quite effective in suppressing sky glare
and actually brightens rather than dims a landscape.
The nature and definitions of the various classes of glare are
1 " Light : Its Use and Misuse ". (7th ed. April, 1915).
402 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
dealt with at greater length in the Report No. I. The general
properties of diffusing media are dealt with in the first report
on diffusing media, while considerable data on the reflecting
power and gloss of papers is contained in Report No. 4 on papers.
Nelson M. Black,
J. R. Cravath,
F. H. Gilpin,
M. Luckiesh,
F. K. Richtmyer,
F. A. Vaughn,
P. G. Nutting, Chairman.
SUBMARINE PHOTOGRAPHY
SUBMARINE PHOTOGRAPHY.*
403
BY J. E. WILLIAMSON.
The taking of pictures under and through water has been
attempted by several investigators — notably, M. Louis Boutan,
Mr. Jaques Reighard of the University of Michigan, Mr. Etienne
Peau and Dr. Francis Ward of Eipswich, England. Of these,.
Dr. Ward had the best results. On his estate in England he con-
Fig. 1. — A tube used in submarine photography.
structed an artificial pond, having a cement well with a large plate
glass window at one side of the pond. As a result of his experi-
ments he stated that he believed under the most favorable condi-
tions it would be possible to photograph through 3 feet (0.91 m.)
of water.
The actual taking of the pictures is not difficult. The main
* Abstract of a paper read at a meeting of the New York Section of the Illuminating
Engineering Society, January 14, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced bv contributors.
404 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
requisite is to get beneath the water and be able to remain there
in comfort under normal atmospheric conditions. The author
and his associates1 have accomplished this by means of the
Williamson submarine tube (Fig. i). This consists of a water-
tight collapsible tube, containing a chamber at its lower end of
sufficient size to hold a man and a camera. The tube is lowered
through an opening in the center of a boat specially constructed
for this purpose. The chamber has a heavy glass plate to with-
stand the water pressure. Through this plate photographs can
be taken. In the West Indies, where the water is very clear,
both day and night pictures have been taken at considerable
depths, which show objects clearly at distances of ioo feet
(30.5 m.) from the camera. Daylight illumination, coming down
through the water, is supplemented by the light from a bank of
quartz-tube, mercury-vapor, arc lamps, which are placed in special
water-tight housings and lowered over the stern of the ship.
Fig. 1 shows a diagrammatic sketch of the apparatus in service.
1 Williamson Submarine Film Corporation.
hurley: street lighting 405
STREET LIGHTING WITH MODERN ARC LAMPS.*
BY W. P. HURLEY.
Arc Lamp Development. — The original commercial arc lamp
system used for street lighting in America was of the open arc
type, which came into commercial use about 1880. This lamp
was usually operated in series on a direct current from special
arc lighting generators. These lamps gave a very unsteady light
with relatively high maintenance cost, due to the short carbon life
and frequent trimming.
The enclosed carbon arc lamps for both alternating current and
direct current came on the market about 1890 and were very
popular in America because they were much steadier than the
open arcs; and, owing to a carbon life of from 100 to 150 hours,
requiring less labor, were much more economical to maintain.
Their efficiency, however, was slightly less than the open arc.
The metallic flame or magnetite arc lamp was developed about
1906; it was essentially a low current, long-burning lamp of com-
paratively high efficiency. Owing to the nature of the electrodes,
however, it could be made only for direct current. By reason of its
very economical maintenance and good efficiency, many thousands
of the previous types of arc lamps were superseded by this
lamp, and it remained as the highest type of arc lamp development
for the lighting of residence streets.
Flame carbon arc lamps were first developed in Europe and
marketed about 1906. These lamps were very expensive, burning
from 10 to 17 hours with comparatively expensive carbons, so
that their use for street lighting in America was never very
popular.
In 191 1 a long-burning flame carbon arc lamp was developed,
this being more in the nature of an enclosed arc lamp to burn im-
pregnated carbons, with special devices for steadying the arc
and keeping the globes clear of deposit from the arc. The long-
burning flame carbon arc lamp is inherently of very high effi-
ciency and, as the energy cost in any street lighting system is
* Abstract of a paper read before the Pittsburgh Section of the Illuminating Engi-
neering Society, May 7, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced bv contributors.
406 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
approximately 50 per cent, of the total cost, including interest and
depreciation on the equipment, it can be readily seen that where
this unit is adapted its extremely high efficiency makes it superior
to any other type. The lamp is inherently of high candlepower
and cannot be practically applied where low intensity is required.
It is suitable for either alternating or direct current and admits
of a wide application.
For residence street lighting, the metallic flame lamp is recom-
mended, as the intensity and color are most suitable for the usual
requirements. Where very small lamps are required, as in out-
lying districts or alleys, small incandescent lamps should be
operated in series with the arc lamps.
For business streets or "white way" lighting where relatively
high intensities are required and the limitations of economy per
unit are not so essential, as in residence districts, because the
population per square foot of street area to be illuminated is
higher, the flame carbon arc lamp is excellently adapted. It
can be supplied in either a pendent or an ornamental post or
bracket lamp, the mechanism being comparatively simple and
practically the same in the two types.
For "white way" lighting, appearance of the street is the most
essential. The arc lamp with its clear, white light contrasting
favorably with the store window lighting always causes favorable
comments. The intensity of the light is relatively high, so that
large units can be employed profitably, thus reducing the number
of poles and the first cost of the installation — at the same time
taking advantage of the highest efficiency and economy in the use
of energy.
Further developments in the way of luminous efficiency are
most favorable to arc lamp development, as chemical limitations
rather than physical are preeminent in this line, and the field of
selective radiation of light has been as yet but slightly touched
upon.
TRANSACTIONS
OF THE
Illuminating Engineering Society
Vol. X AUGUST 30, 1915 NO. 6
THE EFFICIENCY OF THE EYE UNDER DIFFERENT
CONDITIONS OF LIGHTING: THE EFFECT
OF VARYING THE DISTRIBUTION
FACTORS AND INTENSITY.*
BY C. E. EERREE AND GERTRUDE RAND,
BRYN MAWR COLLEGE.
Synopsis: In a previous paper** a plan of work was outlined by one
of the writers for the study of the effect of different kinds of lighting
conditions on the eye. The problem was divided into three parts: (i) the
determination of the conditions that give in general the highest level or
scale of visual efficiency; (2) the conditions that give the least loss of
efficiency for continued work; and (3) the determination of the conditions
that cause the least discomfort. Tests were described especially designed
to meet the requirements of each of these divisions of the work and
results were given to show in a general way the sensitivity of the tests
employed. The work of the present paper is confined to the second divi-
sion of the problem and should be considered as an explorative investiga-
tion for the determination of factors. Six aspects of lighting are con-
sidered provisionally as sustaining an important relation to the eye: the
evenness of the illumination, the diffuseness of light, the angle at which
ght falls on the object viewed, the evenness of surface brightness,
intensity and quality. Only the first five of these are dealt with in this
paper. The first four are called, for convenience of reference, distribution
factors. In order to produce the variation in the distribution factors
needed for the purposes of the test, three types of reflectors in common use
were employed — a direct, a semi-indirect, and an indirect. These reflec-
s were selected with reference to the object of the investigation rather
than as representative in every case of any particular principle of lighting.
The illumination effects produced in each case were specified in the fol-
lowing ways : ( 1 ) A determination was made of the average illumination
the room under each of the three installations. (2) The brightness of
prominent objects in the room, such as the test card, the reflectors for the
emi-indirect installation, the reading page, specular reflection from sur-
aces, etc., was given. (3) Photographs were made of the room from
hree positions under each kind of installation. These effects were then
correlated with the results obtained with the eye test.
In order to determine the effect of varying intensity with a certain
grouping of distribution factors, lamps of different wattage were used
with each type of reflector employed in the distribution series. The
writ.*™ ^'ef rNP°rt uf the work described »n this paper was read by one of the
*££ he.edrr:tV^sbhuergh:VSererLC^V^30n * *° IUumin»tin« Engineering
oPi„ionhs\dvr«daby!om"fbXlng ^^ ^ ^ reSP°nsible for the statements or
** Trans. I. E. S.. p. 40, vol. VIII (1913).
408 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
illumination effects produced were specified by illumination and brightness
measurements in the way described above, and the effects were again
correlated with the results of the eye tests conducted at each intensity of
illumination.
I. INTRODUCTION.
In a paper1 presented to the annual convention of this society
last year, a plan of work was outlined by one of the writers for
the study of the effect of different kinds of lighting conditions
on the eye. The problem was divided into three parts : ( i ) the
determination of the conditions that give in general the highest
level or scale of visual efficiency, (2) the determination of the
conditions that give the least loss of efficiency for continued
work, and (3) the determination of the conditions that cause the
least discomfort. Tests were described which seemed to the
writer after six months of trial to be adequate for the require-
ments of each of these three divisions of work, and results were
given to show in a general way the sensitivity of the tests em-
ployed. With the beginning of the present year work on the
problem proper was begun. This work has been confined to the
second division of the problem, namely, the determination of
the conditions that give the least loss of efficiency as the result
of a period of work. It has been thought best to conduct this
investigation at first along broad lines in order to determine in a
general way the conditions that affect the eye's ability to maintain
its efficiency for continuous work. Later a more detailed ex-
amination will be made of the ways in which these conditions
have been worked out in the various types of lighting systems in
existence at this time.
The following aspects of lighting sustain an important relation
to the eye : the evenness of the illumination, the diffuseness of
light, the angle at which the light falls on the object viewed, the
evenness of surface brightness, intensity, and quality. The first
four of these aspects are very closely interrelated, and are apt
to vary together in a concrete lighting situation, although not in
a 1 : 1 ratio. For the purposes of this paper, therefore, which
is the report of an investigation primarily explorative, it will be
convenient to group these aspects together and refer to them as
1 Ferree, C. E., Tests for the Efficiency of the Eye under Different Systems of
Illumination and a Preliminary Study of the Causes of Discomfort; Trans. I. E- S.,
1913, Vol. VIII, pp. 40-61.
FEKREE AND RAM): EFFICIENCY OF THE EYE 409
the distribution of light and surface brightness in the field of
vision, or still more generally as distribution. In later work an
attempt will be made to study the effect of varying each in separ-
ation, but in the work here reported upon, no especial attempt has
been made to do this. The ideal condition with regard to dis-
tribution is to have the field of vision uniformly illuminated with
light well diffused and no extremes of surface brightness. When
this condition is attained the illumination of the retina will shade
off more or less gradually from center to periphery, which grad-
ation is necessary for accurate and comfortable fixation and ac-
commodation. Up to the present time, we have been able to finish
in as complete a way as we wish for the installations used the
work on distribution and part of the work on intensity. The
remainder of the work will be completed early in the course of
the present year.
The factors we have grouped under the heading distribution
can most conveniently be discussed with reference to four types
of lighting in common use to-day: illumination by daylight,
illumination by direct lighting systems, by indirect lighting sys-
tems, and by semi-indirect systems. In the proper illumination
of a room by daylight we have been able thus far to get the best
conditions of distribution. Before it reaches our windows or
skylights, daylight has been rendered widely diffuse by innumer-
able reflections, and the windows and skylights themselves acting
as sources have a broad area and a low intrinsic brilliancy, all of
which features contribute towards giving the ideal condition of
distribution stated above, namely, that the field of vision shall
be uniformly illuminated with light well diffused and that there
shall be no extremes of surface brightness. Of the systems of
artificial lighting, the best distribution effects from the standpoint
of the comfort and efficiency of the eye are, speaking in general
terms, given perhaps by the indirect systems. In this type of
system the source is concealed from the eye and the light is thrown
against the ceiling or some other diffusely reflecting surface in
such a way that it suffers one or more reflections before it reaches
the eye. The direct lighting systems are designed to send the
light directly to the plane of work. There is in the use of these
systems a tendency to concentrate the light on the plane of work
or object viewed rather than to diffuse it, and, therefore, a ten-
4IO TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
dency to emphasize brightness extremes in the field of vision
rather than to level them down. Too often, too, the eye is not
properly shielded from the primary source of light, and fre-
quently no attempt at all is made to do this. The semi-indirect
systems are intended to represent a compromise between the
direct and the indirect systems. A part of the light is transmitted
directly to the plane of work through the translucent reflectors
placed beneath, and a part is reflected to the ceiling. Thus, de-
pending upon the density of the reflector, this type of system may
vary between the totally direct and totally indirect as extremes and
share in the relative merits and demerits of each in proportion to
its place in the scale. It is not our purpose, however, at this time
to attempt a final rating of the comparative merits of types of
lighting systems. For that our work is still too young. More-
over, there are relatively good and bad fixtures of each type, and
good and bad installations may be made of any system. What
we hope to do is by the appropriate selection and variation of
conditions to find out what the factors are that are of importance
to the eye in lighting, and from this knowledge as a starting point
to work towards reconstruction.
It was stated also in our former paper that the problem dealing
with loss of efficiency presents two phases. We may investigate
(a) whether the eye shows a loss of efficiency after three or four
hours of work under a given lighting system, and (b) whether
there is progressive loss of efficiency in working several months
or years under a given system. We have confined and purpose to
confine our work for the present to the former aspect of the
problem, because it alone falls within the scope of laboratory
studies and because we believe that the problem should be worked
out first in miniature with all the conveniences of manipulation
and possibilities of precision obtaining under laboratory con-
ditions.
II. THE EFFECT OF VARIATION IN THE DISTRIBUTION OF
LIGHT AND SURFACE BRIGHTNESS ON THE EFFI-
CIENCY OF THE EYE FOR A PERIOD OF WORK.
In order better to understand the data given in the tables of
results, the nature of the tests used in this part of the work will
again be briefly called to mind. It will be remembered that the
conventional tests for the eye's responsiveness to its stimulus,
FERREE AND RAND: EFFICIENCY OF THE EYE 411
namely, tests for brightness sensitivity, color sensitivity, and
visual acuity, were found to be practically useless for this work.
Modified and rendered sensitive in the ways described in the
previous paper, they were found to serve as a measure of the
general level of efficiency of the un fatigued eye under different
conditions of lighting; but they failed to show loss of efficiency
as the result of a period of work. This is clue to the following
reasons, (a) There is doubtless very little, if any, loss of
sensitivity to brightness and color during this length of time.2
It is commonly believed, in fact, that the brightness and color
processes are compensating in nature. And (b) the visual acuity
test, in spite of the fact that its results may be ascribed prac-
tically entirely to changes in the muscular control of the eye,
is not adapted to show loss in muscular efficiency, because
the muscles of the eye, while they may have fallen off enormously
in efficiency, can under the spur of the will be whipped up to
their normal power long enough to make the judgment required
by the test. But they can not long sustain this extra effort. This
consideration, it will be remembered, led us to continue the test
through an interval of time. After considerable experimenta-
tion an interval of three minutes was chosen as best suited for
our purpose. When the observer is required to look at the test
card for three minutes, the test objects, even when the eyes are
fresh, are not seen clearly for the whole time. They are seen
alternately as clear and blurred. The time they are seen clear and
blurred is recorded on a rotating drum upon which a line regis-
tering seconds is also run. From this record the ratio of time
seen clear to time seen blurred is determined. This ratio may
be fairly taken as a measure of the efficiency of the eye for three
minutes of clear seeing at the time the test is taken. In applying
the test to our problem, a record is taken at the beginning and at
the close of work, and the ratios of the time clear and the time
2 That there is practically no loss of sensitivity to brightness and color for this
period of time was shown in our former paper by the results of our tests for bright-
ness and color sensitivity with and without the time element as an aid to the test.
(See also in connection with tests for brightness and color sensitivity, Ferree
and Rand: A Note on the Determination of the Retina's Sensitivity to Colored
Light in Terms of Radiometric Units, Amer. Jour, of Psychol., 1912, Vol. XXIII,
PP- 328-332; An Optics-Room and a Method of Standardizing its Illumination,
Psychol. Rev., 191 2, Vol. XIX, pp. 364-373; Colored After-Image and Contrast
Sensations from Stimuli in which no Color is Sensed, ibid, pp. 195-239; Rand:
The Factors that Influence the Sensitivity of the Retina to Color: A Quantitative
Study and Methods of Standardizing, Psychol. Rev. Monog., 1913, r66 pp.; The
Effect of Changes in the General Illumination of the Retina upon its Sensitivity to
Color, Psychol. Rev., 1912, Vol. XIX, pp. 463-490.
412 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
blurred are compared for the two cases to determine how much
the eye has lost in efficiency as the result of work. Two values
were used for the distance at which the test card was placed
from the eye: (a) the maximal distance at which the test objects
could be seen clearly in the momentary judgment, and (b) a
distance less than this. The latter distance was finally chosen be-
cause for the maximal distance, towards the close of the test even
when the eyes were fresh, the value of the time blurred became
too high, it was found, to make the most effective comparison
of the ratios obtaining at the beginning and at the close of work.
In order to eliminate the memory and fatigue factors which
make it impossible to reproduce results in a series of tests with
the same observer when the conventional Snellen test of visual
acuity is employed, it will be remembered that the test card was
made to consist of one or more simple objects, and the type of
judgment was changed so that results were rendered in terms
of clearness of vision instead of in terms of the ability to recog-
nize a series of letters or characters.3 That is, in this type of
test the observer knows what the objects are, and he records the
time during which he sees them clear and the time he sees them
blurred. A number of test objects were used in the work of last
year : two vertical parallel lines stamped i mm. apart on a white
I
card ; the letters li printed in small type, the figures • ,
I
I
— • — , etc. To these was added this year the figure ^
This form of test object was suggested by the one used in Dr.
Ives' visual acuity apparatus.4 While apparently it gives ex-
s For a further explanation of this point see Tests for the Efficiency of the
Eye under Different Systems of Lighting and a Preliminary Study of the Causes
of Discomfort, Trans. I. E. S., Vol. VIII, 1913, pp. 43-45.
4 The writers wish to state that the test object used by them was similar to
that employed by Dr. Ives only with regard to form. One of the prominent features
of the apparatus used by Dr. Ives, for example, is a device for the control of the
width of the parallel lines and the interspaces, while the figure used by us was
printed on a white card with a fixed width of line and interspace. All that the
writers wish to point out here is that a figure made up of parallel lines and inter-
spaces is not, they believe, the most suitable for work of the kind we are doing
because of the comparatively large mean variation it gives in the ratio, time clear
to time blurred.
The figure was at first made 7 mm. in diameter; but this figure was found to
be too large. It would blur irregularly over its surface, i. e., the edges would
become indistinct when the center was clear and vice versa. The figure finally
adopted was 3.5 mm. in diameter. This size was found to be more satisfactory for
our work.
FERREE AND RAND: EFFICIENCY OF THE EYE 4! 3
cellcnt results for the purpose for which it was adopted by
Dr. Ives, it gives too large a mean variation of ratio, time
clear to time blurred, when the element of time is introduced
into the visual acuity test to be of maximal service in our
work. This is probably because a figure of this form is more
influenced by adaptation, the streaming phenomenon,5 and other
variable physiological conditions of the retina than are. for
example, the letters li. This latter object was found to be far
the most satisfactory for our purpose. When used as test object
the mean variation of the ratio, time clear to time blurred, for
the same observer working under conditions as nearly constant as
possible, is very small indeed.6 Results will be given, therefore,
in this report only for the work in which the letters li were used
as test object.
In our work on distribution the tests were made in a room
30.5 ft. (9.29 m.) long, 22.3 ft. (6.797 m0 wide, and 9.5 ft.
(2.895 m-) high. The artificial lighting was accomplished by
means of two rows of fixtures of four fixtures each. Each row
was 6 ft. (1.828 m.) from the side wall, and the fixtures were
6 ft. apart. The reflectors were 29 in. from the ceiling for the
direct system, and 16 in. for the indirect and semi-indirect. Clear
tungsten lamps were used as source. The voltage was kept
constant by means of a voltmeter and a finely graduated wall
rheostat placed in series with the lighting circuit.
In order to get the desired variation in the distribution of light
and surface brightness in the field of vision required for the
purposes of the test, four types of lighting were selected. One
may be called a direct system ; one an indirect system ; one a
semi-indirect system ; and one was the illumination of a room by
daylight. In case of the direct system, two bulbs making an
angle of 180 deg. were used for each fixture. Directly above the
5 Ferree, C. E., The Streaming Phenomenon, Amer. Jour, of Psychol.. 1908,
19. PP- 484-503; also The Intermittence of Minimal Visual Sensation, Amcr. Jour, of
Psychol.. 1908, Vol. XIX, pp. 112-730.
* The order of magnitude of the mean variation of the test for the fresh eye
was obtained as follows. Beginning at 9 a. m., five three-minute records were run
with a rest period of 20 minutes between each test. This was done with all ob-
servers on several days under each system of lighting employed. The rest period
was taken in each case in a room lighted by daylight facing a wall with an evenly
lighted mat surface. For a single series of five tests, the variations of the time
seen clear in the three-minute period have always fallen within 1 per cent, for all
of the observers we have used and all systems of lighting.
414 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
lights was fastened a slightly concaved porcelain reflector 16 in.
in diameter. This type of fixture was not chosen with an especial
reference to its representative character in any system of com-
mercial classification. It was chosen rather with reference to
the purpose of the test. It may be said, however, that it was the
one in use throughout the building in which the tests were made
and gives effects very similar to much of the lighting in actual
use at the present time. In case of the indirect system, corrugated
mirror reflectors were used enclosed in a brass bowl. For the
semi-indirect system inverted alba reflectors 11 in. in diameter
were employed. The daylight illumination came from three win-
dows all on one side of the room. These windows were so shel-
tered that it was never possible for them to receive light directly
from the sun or from a brilliantly illuminated sky. Moreover,
the light from one of them, the one nearest the observer, was
further diffused by passing through a diffusion sash made of
double thick glass ground on one side.
In order to get the effect of the distribution factors on the eye's
loss of efficiency as the result of a period of work, the tests should
be conducted with the quality and intensity of light made as nearly
equal as possible. The quality of light was made approximately
the same for the three installations of artificial light by using
clear tungsten lamps in each case. It was decided to make the
intensity of light as nearly equal as possible at the point of test,
and to give a supplementary specification of the lighting effects
in the remainder of the room for the three installations of arti-
ficial light.7 At the point of test the light was photometered in
several directions. It was made approximately equal in the plane
of the test card and as nearly as possible equal in the other direc-
tions.
The specification of the lighting effects in the remainder of the
room has been accomplished as follows. (1) A determination
7 We have not as yet made the fuller photometric specification of the room
lighted by daylight with our present arrangement of windows, curtains, etc. We hope
to make the effect of varying the distribution factors in daylight illumination
(employing windows, skylights, etc.) the study of a future study. In this study a
photometric analysis of the illumination effects produced will be made an especial
feature.
ferree and rand: efficiency of the eye 415
has been made of the average illumination of the room under
each of the three installations. The room was laid out in 3-ft.
squares, and illumination measurements were made at 66 of the
intersections of the sides of these squares. Readings were made
in a plane 122 cm. above the floor with the receiving test-plate of
the illuminometer in the horizontal, 45 deg. and 90 deg. positions,
measuring respectively the vertical, 45 deg., and horizontal com-
ponents. The 122 cm. plane was chosen because that was the
height of the test object. (2) A determination was made of the
brightness of prominent objects in the room, such as the test card,
the reflectors for the semi-indirect installation, book of the ob-
server, specular reflection from surfaces, etc. The brightness
measurements were made by means of a Sharp-Millar illumino-
meter with the receiving test plate removed. The instrument was
calibrated against a magnesium oxide surface obtained by de-
positing the oxide from the burning metal on a white card. By
this method the reflecting surfaces were used as detached test
plates. The readings were converted into candlepower per sq. in.
by the following formula : Brightness = Foot-candles/V X 144-
(3) Photographs were made of the room from three positions
under each system of illumination.
In Fig. 1 (see "Further Experiments on the Efficiency of the
Eye under Different Conditions of Lighting," Trans, of the 111.
Eng. Soc, 1915, X, p. 452a)8 the test room is drawn to scale : Plan
of room, north, south, east, and west elevations.9 In the drawing-
plan of room, are shown the 66 stations at which the illumination
measurements were made and the position of the outlets for the
lighting fixtures A, B, C, D, E, F, G, H. In the drawing, east
elevation, the position of the observer at one of the points at
8 The present paper is the second one in a series of three on the efficiency of
the eye under different conditions of lighting. Before it was printed the third
paper had been read at the eighth annual convention of the Illuminating Engineering
Society and printed in the papers for that convention. In this paper it had been
found necessary to repeat some of the data of the second paper for reference. Since
both the second and third papers are now appearing simultaneously, the data that
was repeated in the third paper has been omitted from the second. Wherever this
has been done a cross reference is given to the third paper.
• For the scale drawing of the test-room, for the measurements for the direct
and semi-indirect systems given in Table II, and for the photographs of the test-
room, we are indebted to Mr. C. W. Jordan of the United Gas Improvement Co.
416 TRANSACTIONS 01? ILLUMINATING ENGINEERING SOCIETY
which the tests were taken is represented.10 The other three
positions are indicated by X.
Table I (see Table I, op. cit., p. 454) shows the number and
wattage of the lamps used at outlets A, B, C, D, E, F, G, H ; and
Table IT (see Table II, op. cit., 454-455) gives the illumination
measurements for each of the 66 stations represented in Fig. 1,
made with the receiving test plate of the photometer in the hori-
zontal, vertical, and 45 deg. planes.
Table III has been compiled as a supplement to Table II for the
purpose of making a comparative showing of the evenness of il-
lumination at the 122 cm. level given by the three systems of light-
ing. Two cases may be made of this : ( I ) A comparison may be
made of a given component from station to station; or (2) the
difference between the components may be compared. To facil-
itate the comparisons, (a) the mean variation from the average
of each of the components has been computed; and (b) the dif-
ference in the averages of the three components has been deter-
mined. Results for the first of these points are shown in Division
A of the table; for the second in Division B.11
10 The track along which the test card was moved was parallel to the east and west
walls of the room. During the three hours of reading which intervened between
the two tests the observer moved just far enough back from the upright supporting
the mouthboard to give room for the book to be held and to permit of a comfortable
reading position. The book was elevated and held approximately at an angle of 45 deg.
When taking the test, the observer faced the north wall of the room, in such a
position that with the eyes in the primary position, the lines of regard were para'lel
with the east and west walls of the room. Care was taken to have print of uniform
size and distinctness for use with the three systems, and to have a page which
gave a comparatively small amount of specular reflection. The brightness values of
the page in the horizontal and 45 deg. positions for the three systems, are given in
the legends for Figs. 8, 9, and 10.
11 It would be interesting to make this comparison for other levels in the room
and for a greater number of components. But unfortunately we have not been able
to make the number of measurements needed for this comparison. The evenness of
the illumination, it will be remembered, is not only of importance to the efficiency
of the eye with reference to the object directly viewed, but also in its influence on
the distribution of surface brightness. The evenness of surface brightness depends
in general upon two sets of factors: (a) the nature and position of the reflecting
surfaces in the room; and (b) the type of delivery of light to these surfaces.
We realize that the evenness of the illumination on the I22_ cm. plane given by
the indirect and semi-indirect units was somewhat interfered with by the reflectors
of the direct system which were beneath and a little to the right of these units
when in position for the test. Also the evenness of surface brightness on the
ceiling for the direct system was interfered with by the indirect and semi-indirect
reflectors, which were above and a little to the side of the direct units. The in-
fluence of this "dead apparatus" will be eliminated in the next series of installa-
tions. Moreover, the installation in each case was not such as to give the best
effects obtainable from the type of reflector used. For example, the indirect re-
flectors were too close to the ceiling to give the maximum evenness of illumination
and of surface brightness for the type of reflector used. The above analysis of
effects is, therefore, not made for the purpose of drawing general conclusions with
retrard to the type of reflector employed. It is made solely for the sake of the
comparison of the illuminating effects obtained with the corresponding results for
loss of efficiency.
TABLE III.1-'— (Distribution Series).
Compiled from Table II to show a comparison of the evenness of the illu-
mination at the 122 cm. level given by the direct, semi-indirect, and indirect
systems. Division A shows the mean variation from the average for each of
the three components of illumination ; Division B, the difference in the
average value of the three components.
Division A.
Direct
Semi-indirect
Indirect
Mean variation of the components Percentage of mean variation of
components
Vertical Horizontal
1.88
1.68
i.i
1.09
0.66
0.4
i-53
1.32
0.61
Vertical Horizontal
3«%
39%
30 #
47%
42%
37%
32%
36',
19%
System
Division B.
Difference between components
Vertical
and
Horizontal
Vertical 450
and and
45° Horizontal
Direct 2.68
Semi-indirect.. 2.68
Indirect 2.13
0.23
0.64
031
2-45
2.04
1.82
Percentage of difference between
components
Vertical
and
Horizontal
54 ^
63%
59%
Vertical
and
45°
5%
15%
9%
45°
and
Horizontal
51%
56%
55%
■ For Tables I and II, see Tables I and II, Further Experiments on the
Efficiency of the Eye, etc., Trans. I. E. S., 1915, Vol. X, pp. 454-455.
Fig. 2. — Showing the test room illuminated by the direct system. The photograph was
taken from the south end of the room at a point 4 ft. from the west wall.
Fig. 3. — Showing the test room illuminated by the semi-indirect system. The photograph
was taken from the south end of the room at a point 4 ft. from the west wall.
Fig. 4.— Showing the test room illuminated by the indirect system. The photograph
was taken from the south end of the room at a point 4 ft. from the west wall.
Fig. 5.— Showing the illumination effects for the west wall of the room, direct system.
Fig, 6.— Showing the illumination for the west wall of the room, semi-indirect system.
Fig. 7.*— Showing the illumination effects for the west wall of the room, indirect system.
* For Figs. 8, 9, and 10, see Figs. 2, 3, and 4, " Further Experiments on the Efficiency of
the Eye, etc." Trans, of the I. E. S., 1915, Vol. X, pp. 4528-4520.
FERRFE AND RAND: EFFICIENCY OF THE EYE 41/
In Figs. 2 to 10 are given photographs showing the illumination
of the room and the distribution of surface brightness for the
three systems. Figs. 2, 3 and 4 are taken from the south end of
the room at a point 4 ft. from the west wall. These photographs
were taken so as to comprehend as much of the room as was pos-
sible in one view. They include the greater part of the ceiling,
floor, and north wall ; six of the fixtures ; and about one-half of
the east wall. The difference in surface brightness for the various
points of the room (including the lighting units) is, it will be
noted, greatest for the direct system, next greatest for the semi-
indirect system, and least for the indirect system. The indirect
and semi-indirect reflectors were attached to arms of approxi-
mately equal length which could be revolved about the fixture
stem as an axis. When the tests were taken, these reflectors were
turned in each case to the inside position indicated in the photo-
graph, the object being to have the two types of reflectors as
nearly as possible in the same position in the field of vision for the
comparative tests. The direct fixtures, it will be noted, were below
and slightly outside this position. In our next series of experi-
ments, arrangements have been made such that the reflectors can
be placed in exactly the same position for each type of installation
when it suits the needs of the experiment to have it so. The
slight deviation from exact coincidence found in these experi-
ments is. however, perhaps of no great consequence for the pur-
pose of the present work especially in the case of the indirect and
semi-indirect reflectors. In Figs. 5. 6 and 7, are represented the
illumination effects for the west half of the room. These photo-
graphs show the distribution of light and shade on the greater part
of the west wall, and the adjacent ceiling, and include two of the
fixtures. In Figs. 8, 9 and 10 (see Figs. 2-4. op. cit. pp. 452a-452b )
are shown the brightness measurements of all surfaces having
very high or very low brilliancy. The spot measured is indicated
by a cross, and the numerical value of the brightness measurement
in candlepower per square inch is printed nearby. These spots
are also lettered for convenience of reference in the intensity
series. That is. since several installations were used in the in-
tensity series it was found convenient to express these values in
tabular form and to identify them with the surfaces measured
418 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
by means of letters. These photographs were taken from a point
in the line with the four positions of the observer as near to the
south wall of the room as was possible, but owing to the narrow
field of the camera as compared with the binocular field, these
views include, for example, only about one-half of the field of
vision of the observer at the test station nearest to this end of
the room. The camera's field in this position corresponds in fact
very closely to the field presented to the observer seated at the
center of the room. While, therefore, not all of his field of
view for all the positions at which tests were made is covered by
the brightness measurements shown in the photographs, still the
order of magnitude of brightness differences present in the field
of vision for the different systems is well represented by these
measurements, as can be seen by an inspection of the preceding
photographs and from the descriptions of the installations used.
In order to facilitate certain features of comparison such as,
for example, of the evenness of surface brightness for each sys-
tem for all of the room, for all but the sources or the sources and
spots above the sources, the brightness measurements shown in
Figs. 8, 9 and 10 are also given in tabular form. These measure-
ments and the letters identifying them with the surfaces measured
are given in Table IV and V. (see Table III and IV, op. cit.,
p. 457). In making a comparison it should be noted that the spots
measured are not in all cases identical for the three systems.
That is, owing to the different effects produced by the different
reflectors, the same spot was not always conspicuously light or
dark for the three systems. The letters E, F, G, etc. may refer,
then, to entirely different spots in case of the three systems.
In Tables VI and VII (see Table V and VI, op. cit., pp. 463-
464) are shown some prominent ratios of surface brightness for
the three systems.13 In representing these ratios it has been consid-
13 In attempting to make comparisons of the effect of the different magnitudes
of brightness ratios, one obviously must bear in mind that the surfaces between
which the ratios are established are not in all cases in the same position in the
field of vision for the three systems. For example, the brightest surfaces in case
of the indirect system, namely, the spots on the ceiling directly above the reflectors
are farther removed from the direct line of vision of the observer when in the
working position than were the brightest surfaces in case of the direct and semi-
indirect systems. The position of the Surface in the field of vision would come into
question, for example, in making a determination of the maximum value of bright-
ness difference that the eye is adapted to stand. While we have done a great deal
[Continued on next page.)
1-KKkKK AND RAND: I'.FF Id l-.NCV OF Till". I'.YK 419
ered important to make a comparative showing for the three sys-
tems (a) of the extremes of surface brightness; and (b) of the
relation of the brilliancy of objects in the surrounding field to the
surface brightness at the point of work. The extremes of sur-
face brightness are shown by giving the ratios between surfaces
of the first, second, third, etc., order of brilliancy and the sur-
face of the lowest order of brilliancy ; and the comparison of the
brilliancy of objects in the surrounding field to the brightness at
the point of work by giving the ratios of the surfaces of the first,
second, and third order of brilliancy to the brightness of the test
card and the reading page in the working position. The follow-
ing points may be noted. ( 1 ) The illumination effects produced
by the direct system are characterized by great extremes of sur-
face brightness and a high ratio of brilliancy of objects in the
surrounding field to the surface brightness at the point of work.
These effects are much less pronounced for the semi-indirect
system, and still less for the indirect. (2) A comparison of this
table with the tables showing loss of efficiency as the result of
work shows that while the extremes of brightness are enormously
larger for the direct than for the semi-indirect system, the eye
loses almost as much in efficiency for three hours of work under
the semi-indirect system as under the direct. That is, the great-
est ratio of brightness for the direct system is over 1,000 times
as much as the greatest ratio for the semi-indirect, while the
difference in loss of efficiency for the two systems is compar-
atively insignificant. On the other hand the greatest ratio of
brightness for the semi-indirect system is only about five times
as much as for the indirect and the difference in loss of efficiency
for three hours of work is very large, this loss of efficiency for
three hours of work for the indirect system being, it will be noted,
of work on the effect of position of the brilliant surface in the field of vision in our
investigation of the causes of discomfort, we have made no especial investigation of
this point in relation to loss of efficiency. Doubtless what we shall all have to bear
in mind is that even in the end we can not hope to specify narrowly what is most fav-
orable, etc. in lighting conditions. The factors that enter into the concrete lighting situ-
ation are so complex, or rather are so variable and so rarely duplicated that we can
hope to make general specifications with regard to what is most favorable, for ex-
ample, only within very broad limits. If one wishes to work the conditions down
to a finer point than this, the particular installation must itself be tested in situ. We
are at present working on a shorter test which we hope will serve this purpose
better than the test which has been used in the work described in this paper.
2
420 Transactions of illuminating engineering society
very small indeed. This seems to indicate (a) that for the scale
of magnitudes present in this series of experiments, the gradation
of surface brightness for the indirect system is very close to what
the eye is prepared to stand without loss of efficiency; and (b)
that an increase in differences in brightness above this point is
followed at first by a rapid increase in loss of efficiency and
later by a much slower increase. In the intensity series the
following points also come out. (i) The effect of size of ratio
on loss of efficiency is different for different orders of magnitude
of brightness. That is, for the range of scale of magnitudes we
have used, the lower is the order of magnitude, the greater is the
ratio that is permissible. And (2) the size of the brilliant object
as well as its brilliancy is of importance. That is, within certain
limits, as yet undefined, an increase in the area of the brilliant
surface causes an increase in loss of efficiency.
Supplementary to Tables IY-VII we have computed for the
three systems the mean variation of the several brightness values
from their average values. While important from the standpoint
of showing the variation from the mean for the different systems,
such a comparison is, however, probably not so important from
the standpoint of the eye as are the comparisons given in Tables
IV-VII. That is, from the standpoint of effect on the eye it is
probably more important to give a representation of the bright-
ness of individual surfaces, more especially of surfaces showing
extremes of brightness, than it is the mean variation from the
average brightness of all the surfaces. In order to make possible
the comparison with and without the source and the spot above
the source, the table is made to show separately the mean varia-
tion for the following measurements: (a) for all; (b) for all
but the source; and (c) for all but the source and the spot above
the source. Results are given in Table VIII.
Obviously the effect of these installations on the eye's ability
to maintain its efficiency for a period of work will vary with
the position of the observer in the room. The tests have been
made, therefore, at four positions : one in which six fixtures were
in the field of view, one in which four were in the field of view,
one in which two were in the field of view, and one in which
none were in the field of view. This variation of position at
FKKREE AND RAND: EFFICIENCY OF THE EYE
421
which the observation was made accomplishes two purposes.
( 1) It gives us a more representative idea of the difference in
the effect on the eye of the four types of lighting. And (2) it
shows the effect of varying the number of surfaces showing
brightness differences, particularly the number of primary
sources in the field of view.
TABLE VIII. "—(Distribution Series).
Compiled from Table IV to show the mean variations in surface bright-
ness for the direct, semi-indirect, and indirect systems.15
Mean variation for the three
systems
Percentage of mean variation for
the three systems
Measurements
considered
Direct
Semi-
indirect
Indirect
Direct
Semi-
indirect
Indirect
All
All but the
All but the
source and the
spot above the
94-977
O.OOlS
0.0016
0.075
0.01817
0.0013
O.0235
O.0235
O.OOI2
189%
33%
32%
145%
120%
30%
135%
135%
35%
" For Tables IV-VII, see Tables III- VI, Further Experiments on the Ef-
ficiency of the Eye, etc., Trans. I, E. S.( 1915? Vol. X, pp. 457, 463-464.
15 It is scarcely necessary to point out that the above results seem to indicate
that the great advantage of the indirect over the other systems of lighting we have
used with regard to the factor: evenness of surface brightness, comes primarily at
least from its provision for shielding the eye from the light source rather than
from any conspicuously greater evenness of illumination given by it to the objects
in the field of view. In fact all of the systems give a fairly even distribution of
surface brightness outside of the source and the surfaces immediately surrounding
it.
The need of keeping the surface brightness within certain limits and the
primary importance of properly shielding the eye from the source to the accom-
plishment of this desideratum are both obvious Doubtless many ways will be de-
vised in course of time for cutting down useless and harmful brightness differences in
lighting effects. For example, the possibility is here suggested of producing a still
smaller brightness difference than is given by the indirect reflectors of the type we
have employed, by using semi-indirect reflectors of such a density as to give a
surface brilliancy equal to that of the spot of light cast upon the ceiling. The
value of this brilliancy, because of the larger area of luminous surface presented,
could then be made smaller than that of the ceiling spot cast by the indirect
reflector and still give the same amount of light to the room. A similar effect
may be obtained with the indirect reflector by using lamps of lower wattage and
adding the light needed to make up the deficiency by installing directly beneath the
reflector lamps of low wattage in translucent enclosures of a density that will
give a surface brilliancy equal to that of the ceiling spots. The eTfect of both
of these devices would be to lower the surface brilliancy for a given light flux
by increasing the area of the luminous surface. Whether either would be advisable
from other standpoints we are not at present prepared to say.
422 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Results will be given in this paper only for the position with
six fixtures in the field of view. The results for the other posi-
tions will be given in a later paper. When working at the posi-
tion with six fixtures in the field of view, our tests show that the
eye loses practically nothing in efficiency as the result of three to
four hours of work under daylight, it loses enormously for the
same period of work under the direct installation, and almost as
much under the semi-indirect installation. Under the indirect
installation the eye loses a little more than under daylight, but
not nearly so much as under the other installations.
The results of the work on distribution are given in Tables
IX and X. Early in the work it was found that nearly as
much difference in result was gotten for two as for three hours
of work. In Table IX is shown the loss in efficiency for Ob-
server R for three hours of work under the four systems ; and
in Table X, the loss in efficiency for Observer G for two hours
of work. These tables are typical of the results obtained from
all of our observers for these periods of work.16 Column i of
these tables gives the type of lighting system. Column 2 gives
the total wattage of the lamps used, and Column 3 the voltage at
which these lamps were operated. Columns 4, 5, and 6 give the
foot-candles of illumination at the point of work measured re-
spectively in the horizontal, vertical, and 45 deg. planes. Column
7 gives the maximal distance at which the test object could be
seen clearly, and Column 8 the distance chosen at which to con-
duct the test for loss of efficiency. Care was taken in every case
to choose this working distance of such a value that the ratio it
sustained to the maximum distance was always approximately
the same. Column 9 gives the total time the test object was seen
clear in the three minutes of observation and Column 10 the total
time it was seen blurred. Column 11 gives the ratio of the total
time seen clear to the total time seen blurred, and Column 12
gives the comparative values of these ratios in terms of a com-
mon standard. These ratios were reduced to a common scale or
standard in order to make the comparison of the amounts of
16 Obviously in the consideration of the effect of a given lighting system on
the ability of the eye to hold its efficiency for a period of work, the age of the
observer and the condition of his eyes should be taken into account. For a full
clinic report of the eyes of the observers employed, see op. cit., foot-note 14, p. 460.
FKRREE AND RAND: EFFICIENCY OF THE BYE 423
change in their ratios easier. They express the comparative
ability of the eye to sustain its power of clear seeing for three
minutes before and after work for the four conditions of light-
ing used.
It will also be noted from Column 8 of the above tables that
the visual acuity tests show that acuity of vision as determined by
the momentary judgment is higher for the same foot-candles of
illumination under daylight than under artificial light, and of the
artificial lights it is very slightly highest for the indirect system,
next highest for the semi-indirect system, and slightly lowest for
the direct. It will thus be seen that for all the purposes of clear
seeing, whether the criterion be maximal acuity or the ability of
the eye to hold its efficiency for a period of work, the best re-
sults are given in order by the systems that give the best distri-
bution. The effect of distribution, however, on the ability of the
fresh eye to see clearly, is not nearly so great as it is on its power
to hold its efficiency for a period of work.
In order to give a typical representation in graphic form of
the effect on the efficiency of the eye of a period of work under
these four conditions of lighting, the results of the above tables
will also be given in the form of a chart made up of straight
lines showing in each case the loss of efficiency from beginning
to close of work. In constructing these charts, the length of time
of work is plotted along the abscissa, and the ratio of the time
the test object is seen clear to the time it is seen blurred is
plotted along the ordinate. Each one of the large squares along
the abscissa represents one hour of work and along the ordinate
an integer of the ratio. Chart A shows the results for Table IX,
and Chart B for Table X. An inspection of these charts will
show how widely different in amount is the loss in efficiency
under the specified conditions for the direct and semi-indirect
systems as compared with the indirect system and daylight, and
how close is the correspondence between the results for the
direct and semi-indirect system, and between the results for the
indirect system and daylight.
The loss in efficiency found in the above work seems to be
predominantly, if not entirely, muscular, for the tests for the
sensitivity of the retina show practically no loss in sensitivity
424 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
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FERKEE AND RAND: EFFICIENCY OF THE EVE
425
Chart A (Observer R). — Showing the eye's loss in efficiency as the
ICStllt of three hours of work under the systems of indirect, semi-indirect
and direct lighting employed as compared with daylight.
Lighting system Watts
A— Daylight —
B— Indirect 800
C — Semi-indirect . .. 760
D— Direct S80
Foot-candles
(folta
Horizontal
Vertical
45°
—
5-5
1-32
4.2
107
5-2
1.36
3-5
107
5-3
1-45
4.0
107
4.2
1.41
2.6
8
D
1 I
Chart A.
Chart B (Observer G). — Shows the eye's loss in efficiency as the result
of two hours of work under the systems of indirect, semi-indirect and direct
lighting employed as compared with daylight.
lighting system Watts
A— Daylight —
B — Indirect 800
C — Semi-indirect . . . 760
D— Direct 880
Foot-
candles
'olts
Horizontal
Vertical
45°
—
5-5
'•32
4-2
107
52
1.36
3-5
107
5-S
1-45
4.0
107
4.2
I-4I
2.6
3
1
Chart B.
426 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
as the result of work under any of the installations employed.17
The following reasons are suggested why the muscles of the eye
giving both fixation and accommodation should be subjected to
a greater strain by the direct and semi-indirect installations than
by the indirect installation or daylight. (1) The bright images
of the sources falling on the peripheral retina, which is in a
perpetual state of darkness-adaptation as compared with the
central retina, and is, therefore, extremely sensitive in its re-
action to such intensive stimuli, set up a reflex tendency for the
eye to fixate them instead of, for example, the letters which the
observer is required to read. (2) Likewise a strong reflex tend-
ency to accommodate for these brilliant sources of light, all at
different distances from each other and the lettered page, is set
up. (3) These brilliant images, falling on a part of the retina
that is not adapted to them, causing as they do acute discomfort
in a very short period of time, doubtless induce spasmodic con-
tractions of the muscles which both disturb the clearness of
vision and greatly accentuate the fatiguing of the muscles. The
net result of all these causes is excessive strain which shows
itself in a loss of power to do work. In the illumination of a
room by daylight, however, with a proper distribution of win-
dows, the situation is quite different. The field of vision con-
tains no bright sources of light to disturb fixation and accommo-
dation and to cause spasmodic muscular disturbances due to the
action of the intensive light sources on the dark-adapted and
sensitive peripheral retina. As we have already pointed out,
the light waves have suffered innumerable reflections and the
light has become diffuse. The field of vision is, comparatively
speaking, uniformly illuminated, and there are no extremes of
surface brightness. The illumination of the retina, therefore,
falls off more or less gradually from center to periphery, as it
should to permit of fixation and accommodation for a given
object with a minimum amount of strain.
11 In the next paper of the series it is shown (see op. cit. pp. 484-490) that the
loss in muscular efficiency is confined largely to the accommodation muscles. The
fixation muscles apparently suffer little loss for the period of work we have used.
FERREE AND RAND: EFFICIENCY OF THE BYE 427
III. THE EFFECT OF VARIATION IN THE INTENSITY OF
LIGHT ON THE EFFICIENCY OF THE EYE FOR A
PERIOD OF WORK.
It is not our purpose, however, to contend that distribution
of light and surface brightness in the field of vision is the only
factor of importance in the illumination of a room. The in-
tensity and quality of light must also be taken into account. For
example, one of the most persistent questions asked by the il-
luminating engineer is : "How much light should be used with a
given lighting installation to give the best results for seeing?"
We have undertaken, therefore, to determine the most favor-
able range of intensity for the four types of lighting we have
used. Our work shows in general the following results. A
very wide range of intensity is permissible for daylight, and a
comparatively wide range for the indirect installation. For
the semi-indirect installation the eye fell off heavily in efficiency
for all intensities with exception of a narrow range on either
side of 2.2 foot-candles measured at the level of the eye at the
point of work with the receiving surface of the photometer in
the horizontal plane. For the direct installation no intensity
could be found for which the eye did not lose a very great deal
in efficiency as the result of work. Thus it seems that the factors
we have grouped under the heading distribution are funda-
mental. That is, if the light is well distributed and diffuse, as it
was in case of the daylight and indirect installations we used,
and there are no extremes of surface brightness, the ability of
the eye to hold its efficiency is, within limits, independent of
intensity. In short, the retina is itself highly accommodative
or adaptive to intensity, and if there is the proper distribution
and diffuseness of light and the proper gradation of surface
brightness in the field of vision, the conditions are not present
which cause strain and consequent loss in efficiency in the ad-
justment of the eye. The results of this series of tests, then,
accomplish two purposes, (i) They show that when the dis-
tribution and diffuseness of light and the distribution of surface
brightness in the field of view are properly taken care of, the
eye, so far as the problem of lighting is concerned, is practically
independent of intensity. And (2) they show the effect on the
efficiency of the eye of the variations in surface brightness pro-
428 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
duced by varying intensity in case of the direct and semi-indirect
installations we have used.
The tests were made in the same room, with the same fixtures,
and in general with the same conditions of installation and meth-
ods of working as were described in the work on distribution.
To secure the various degrees of intensity needed, lamps of
different wattage were used. These were selected from a series
of tungsten lamps ranging from 15-100 watts. In order to keep
the distribution factor as nearly constant as possible for a given
type of system, the lamps used in making the test for that type
of system were all of one wattage, i. e., all 15's, 25's, 40's, 6o's,
or ioo's.
For the semi-indirect system the total range of intensity of
illumination employed is shown by the following figures. The
series was begun with 25-watt lamps18 and consisted of 25, 40,
60, and 100-watt lamps.19 For the 25-watt lamps the photometer
reading at the point of work with the receiving test plate of
the photometer in the horizontal plane, showed 1.6 foot-candles;
with the test plate in the vertical position 0.45 foot-candle; in
the 45 deg. position 1.15 foot-candles. For the 100-watt lamps.
6.8 foot-candles were obtained with the test plate horizontal ;
1.82 foot-candles with the test plate vertical; and 4.5 foot-candles
with it in the 45 deg. position. The tests for loss in efficiency20
showed that the intensity most favorable to the eye was secured
18 Since the most favorable intensity was given by the 40-watt lamps and since
the 15-watt lamps gave so little light as to be extremely trying to the eyes, it was
thought best to begin the series with the 25-watt lamps instead of the 15 as was
done in case of the direct system.
19 Owing to their smaller size, socket extenders had to be used for the 25 and
40-watt lamps. That is, without the extenders these lamps came so low in the re-
flector as to change the distribution effects given by the reflector.
20 In conducting these tests it was found necessary to allow a period of
adaptation without work to the illumination of the room before the first test was taken.
If this were not done, especially in case of the lower intensities of light used, the
changing sensitivity of the eye to the intensity of light employed produced a notice-
able change in the visual acuity between the times the tests before and after work were
taken. Since the distance of the test card was kept the same for the two tests, this
change in the visual acuity tended to influence the ratio: time clear to time blurred.
To determine the length of time needed with a given intensity of light to insure a con-
stant acuity so far as adaptation is concerned, preliminary tests were made as follows.
The acuity of the observer was taken every three minutes until no noticeable
change was found. This length of time was then always allowed for that observer
as an adaptation period prior to the loss of efficiency test conducted for the intensity
of illumination.
FERREE AND RAND: EFFICIENCY OF THE EYE 4-"J
when the photometric reading with the test plate in the horizontal
plane showed 2.2 foot-candles ; in the vertical plane, 0.58 foot-
candle; and in the 45 deg. plane, 1.52 foot-candles. The total
wattage in this case was only 320. At this intensity of illumin-
ation the semi-indirect installation, so far as its effect on the eye
is concerned, compares very favorably with the indirect installa-
tion at such ranges of intensity as we have employed. At in-
tensities appreciable higher than this most favorable value,
however, or appreciably lower, the loss in efficiency is very great.
At the intensity commonly recommended in lighting practise, this
semi-indirect installation is almost, if not quite as damaging as
the direct installation. The intensity recommended by the Il-
luminating Engineering Society, for example, in its primer issued
in 1912, ranges from 2-3 to 7-10 foot-candles, depending upon
the kind of work ; 5 foot-candles is taken as a medium value.
This medium value is more than double the amount we have
found to give the least loss in efficiency for the type and installa-
tion of semi-indirect lighting we have used. The intensity we
have found to give the least loss in efficiency for this type of
lighting does not, however, give maximal acuity of vision as
determined by the momentary judgment. At an intensity that
does give maximal acuity of vision as determined by the momen-
tary judgment, the eye runs down rapidly in efficiency. That
is, in this type of lighting one or the other of these features must
be sacrificed. High acuity and little loss in efficiency can not
both be had at the same intensity. These features can both be
had only under daylight and, in case of the installations, we used,
with the indirect system. However, the amount of light we
find to give the least loss in efficiency seems to be sufficient for
much of the work ordinarily done in the office or home. It is
not enough, though, for drafting or other work requiring great
clearness of detail. By giving better distribution effects this sys-
tem is supposed also to be a concession to the welfare of the eye,
but our tests show that this concession is not so great as it is
supposed to be. In fact, installed at the intensity of illumination
ordinarily used, or at an intensity great enough for all kinds of
work, little advantage is gained for the eye in this type of light-
ing with reflectors of low or medium densities ; for with these
430 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
intensities of light and densities of reflector, the brightness of the
source has not been sufficiently reduced to give much relief to the
suffering eye. Until this is done in home, office, and public
lighting, we can not hope to get rid of eye strain with its complex
train of mental and physical disturbances. If the semi-indirect
principle of lighting is to be used with benefit to the eye, a density
of reflector and type of installation must be employed that will
give a gradation of brightness in the field of view in conformity
with the limits of difference that the eye can stand without loss in
efficiency or comfort.
In case of the direct system of lighting, we were able to im-
prove the conditions so far as loss of efficiency of the eye is
concerned, by reducing the intensity ; but this system never proved
to be so favorable in this regard as even the semi-indirect system.
In the tests made under the direct system care was taken to have
the fixtures as nearly as possible in the same position as they
were for the semi-indirect system. Our fixtures for the direct
system were so installed that either one or two lamps could be
used in each fixture, totalling respectively 8 and 16. In order
to get a wider range of intensity both numbers of lamps were
used, i. e., one series was made with 8 lamps and aonther with
16. Four intensities of light were used in each case. These
intensities were secured in the 8-lamp system by using lamps
totalling 120, 200, 320, and 480 watts. The foot-candles at the
point of work ranged from 0.64 with the receiving test plate of
the photometer in the horizontal, 0.32 in the vertical, and 0.49
in the 45 deg. position with the lamps totalling 120 watts, to 2.6
with the test plate in the horizontal, 1.02 in the vertical, and 2.0 in
the 45 deg. position with the lamps totalling 480 watts. The four
intensities were secured in the 16-lamp system by using lamps
totalling 240, 365, 400, and 880 watts. The foot-candles at the
point of work with the 16-lamp system ranged from 1.23 with
the test plate in the horizontal, 0.54 in the vertical, and 0.935 m
the 45 deg. position with the lamps totalling 240 wattts, to 4.2
with the test plate in the horizontal, 1.41 in the vertical, and 2.6
in the 45 deg. position with the lamps totalling 880 watts. The
most favorable intensity was secured by an installation that gave
1. 16 foot-candles with the test plate in the horizontal, 0.45 in the
FERREE and rand: EFFICIENCY OF THE EYE 431
vertical, and 0.85 in the 45 deg. position. This intensity was
given by the 8-lamp system with a total wattage of 200. At this
intensity, however, the loss in the efficiency of the eye for three
hours of work was almost four and one-half times as great as
for the most favorable intensity for the semi-indirect system ; and
more than four and one-half times as great as for a wide range
of intensities for either the indirect system or daylight.
The following specification was made of the illumination effects
for the intensity series. (1) Illumination measurements were
made for the highest intensity employed at the 66 stations in
the test room. These measurements were made in the way de-
scribed in the preceding section. For the other intensities em-
ployed, measurements were made at 9 representative stations to
show in a general way the order of magnitude of reduction
produced by using the lamps of lower wattages. (2) Brightness
measurements were made of prominent objects in the room, such
as the test card, the book of the observer, and all surfaces show-
ing very high or very low brilliancy, for all intensities for all
systems.
In Table XI are given the illumination measurements for the
highest wattages used made with the receiving test plate of the
photometer in the horizontal, vertical, and 45 deg. planes. Tables
XII, XIII and XIV show the illumination measurements for
the other wattages employed in the series at nine representative
stations. These measurements are intended to show the order
of magnitude of reduction of the illumination of the room pro-
duced by using the lamps of lower wattage. They conform in
each case pretty closely, it will be noted, to the simple ratio
of the wattages employed. Tables XV, XVI and XVII give
the brightness measurements for these installations for the dif-
ferent intensities used. The points at which the measurements
were taken are indicated by the letters A, B, C, D, E, F, etc.,
see Figs. 8 and 9. In Tables XVIII, XIX and XX are given the
prominent brightness ratios for the different intensities used.
It was stated in the preceding section that the order of magnitude
of the brightness scale exerts an influence on the effect of bright-
ness ratio on the eye's loss of efficiency. This influence is readily
seen on comparing the results of Table XVIII with those of
432 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Table XXI. That is, while the various brightness ratios remain
pretty much the same for the different intensities of light em-
ployed, the least loss of efficiency was given by the 40-watt lamps.
This loss was, for example, very much less than was given by the
100-watt lamps, not quite so much less than was given by the
60-watt lamps, and very little less than was given by the 25 watt
lamps. The loss in efficiency for the 25-watt lamps can also
doubtless be attributed in part to an insufficient amount of light.
At least the testimony of the various observers was that not
enough light was given by these lamps for ease and comfort
in reading. The results of these experiments seem to show, then,
that a given order of magnitude of brightness difference in the
field of view has more effect on the efficiency of the eye when
the general scale of brightness values is higher than when it is
low.
A comparison of Tables XIX and XX with Tables XXII and
XXIII shows the influence of the area of the bright surface on
the ability of the eye to hold its efficiency for a period of work.
For example, although it is shown in Table XIX that the ratios :
lightest surface to darkest surface, and lightest surface to test
card and reading page, are greater in the 16-lamp system for the
15 than for the 25-watt lamps, Table XXII shows that greater
loss of efficiency is caused by the 25-watt lamps. Similarly,
Table XX shows that in the 8-lamp system these ratios are
greater for the 25 and 40 than for the 60-watt lamps, while
Table XXIII shows that the 60-watt lamps cause the greater loss
in efficiency. This may be explained as follows. The brightest
surfaces in the field of vision for the direct system are the fila-
ments of the lamps. The brightness measurements given in the
table are in terms of candlepower per square inch. The candle-
power per square inch is the same, for example, for the filaments
of the 15 as for those of the 25-watt lamps. But since the darkest
surfaces, the test card, and the reading page, are darker for the
15-watt than for the 25-watt system, the ratios: lightest to
darkest surface, lightest surface to test card, and lightest sur-
face to reading page, are greater for the 15 than for the 25-watt
system. While, however, the candlepower per square inch is the
same for the 15 as for the 25-watt filaments, the actual candle-
FERREE AND RAND: EFFICIENCY OF THE EYE 433
power is less for the 15-watt filaments because of their smaller
area of surface. That is, the area of the brilliant surface or
in terms of luminous effects, its actual candlepower must be
taken into account in estimating the effect on the eye as well as
the candlepower per square inch. The effect of area on sensa-
tion is well known in physiological optics (for example, see
Abney, Philos. Trans., 1897, CXC, A, p. 169), and is expressed
in the law that within limits an increase of area of the stimulus
functions as an increase of intensity, although not in a simple
ratio. Apparently, too, in its effect on the eye's power to main-
tain its efficiency for a period of work, an increase of area of
the brilliant surface also functions within limits as an increase
in intensity.21 Ratios expressed in candlepower per square inch
do not seem therefore, in all cases to be an adequate specification
of surface brightness, so far as its effect on the efficiency of the
eye is concerned, unless the areas compared be the same.
21 The above explanation is, however, not complete. It shows only that the
ratios: lightest to darkest surface, and lightest surface to test card and reading
page, are greater for the is than for the 25-watt lamps because the candlepower
per square inch not the actual candlepower was used in computing the ratios.
We are not at present able to give the ratio of actual candlepower of lightest to
darkest, lightest to reading page, etc., because we did not measure the actual candle-
power of the darkest surface, the reading page, etc., only the candlepower per
square inch. However, since the test card and the reading page were of the same area
in case of the different intensities, and the darkest surface of approximately the same
area, ratios based on the total candlepower of the lightest surface (the lamp
filament) and the candlepower per square inch of the darkest surface, test card, and
reading page have comparative values. These ratios are very little different for the
15- and 25-watt lamps. That is, the ratio lightest to darkest for the 15-watt
lamps zzz 28,698, for the 25-watt lamps =3 28,933; lightest to test card for the
15-watt lamps =r 11,828, for the 25-watt lamps zzs 12,616; lightest to reading page
for the 15-watt lamps z=z 7,352; for the 25-watt lamps zzz. 7,483.
A complete explanation of the result will doubtless involve two factors (1) the
ratio of the actual candlepower of the lightest and darkest surfaces; and (2) the
point brought out in connection with Tables XVIII and XXI, namely that a given
order of magnitude of brightness difference in the field of view has more effect on
the loss of efficiency of the eye when the general scale of brightness values is high
than when it is low. From this we would expect, for example, that if the ratio
lightest to darkest surface and lightest surface to test card and reading page were
equal or approximately so for the 25- and 15-watt lamps, for example, the greater
loss of efficiency should come with the lamps of higher wattage. Similarly for the
8-lamp system, the 60- and 40-watt lamps should cause a greater loss of efficiency
than the 25-watt lamps. The 15-watt lamps with this system gave too little light to
read with ease and comfort hence are ruled out of count in the comparison.
For investigating in detail the effect of area of the brilliant surface on the eye's
loss of efficiency, the campimeter may prove of convenience and of service. This is
one of the instances where the abstract may be used to advantage to supplement the
concrete method of investigation. (See Memorandum on the Report of the Research
Committee, Trans. I. E. S., 1914, Vol. IX, No. 4. p. 358.)
The great difficulty with the abstract type of investigation, as the writers see the
case at this time, is that a determination of what is permissible with regard to one
factor in isolation may not be at all permissible in conjunction with other factors.
A more feasible plan seems to us to be to vary the factor over a certain practical
range in an actual concrete situation. By a proper selection of the concrete situations
employed the ground of all that is practicable in lighting' can be covered, and the
results obtained can have a safe application.
434 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
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FERREE AND RAND: EFFICIENCY OF THE EYE
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436 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
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FERREE AND RAND: EFFICIENCY OF THE BYE
437
TABLE XII. — (Intensity Series.)
Showing the illumination measurements in foot-candles at nine representa-
tive stations for the different intensities used for the semi-indirect system.
Horizontal
Vertical
45°
Station
800
watts
480
watts
320
watts
200
watts
800
watts
480
watts
320
watts
200
watts
800 480 320
watts watts ; watts
200
watts
Card ....
12
16
3i
34
39
45
54
58
Average .
6.8
2.9
6.8
7-4
4.6
4-4
6.8
2.47
5-2
4-44
3-3
1.79
3-2
3-6
2.1
1.79
3-3
1.31
2.82
2.66
2.2
I.O
2.0
2.2
1-45
1. 17
2.2
O.87
r-9
I.78
1.6
o.75
1.32
1.6
o.95
o-93
1.4
0.7
1.44
1. 11
I.82
0.55
0.69
2.2
1.76
1-95
2.65
1.77
2.6
i-93
O.94
0.35
0.44
O.94
0.9
0.86
i-3
1. 15
i-35
1. 16
O.58
O.22
O.23
O.58
O.58
0-54
0.82
O.62
O.87
O.77
0.45
0.17
O.I5
O.44
0.43
O.41
0.58
0.48
0.63
0.48
4-5
I.49
36
5-2
3-4
3.68
5-6
2.65
5.28
4-°3
2.4
0.76
1-75
2.4
1.68
1-52
2.7
1.47
2.68
2.42
1-52
0.51
1.03
i-53
1. 12
o-95
1-7
o-95
1.8
1. 61
115
0.4
0.68
115
0.74
0.73
1. 19
0.76
1-3
1. 01
TABLE XIII.— (Intensity Series.)
Showing the illumination measurements in foot-candles at nine representa-
tive stations for the different intensities used for the direct system (16 lamps).
Station
Card • • -
12
16
3i
34
39
45
54
58
Average
Horizontal
400
watts
1.86
2.6
4.0
2.1
2-35
2-7
2.2
4.0
4-3
2.14
365 240
watts watts
2.1
1-45
4-4
2.1
2-3
2.6
i-75
1.6
2-3
1.23
1-43
2.6
i-45
1.84
i-5
1-45
1-34
2-5
1.26
Vertical
400
watts
0.8
O.44
O.47
O.81
1. 41
1.44
1.27
2.1
1.88
1. 12
365
watts
240
watts
0.6
0.275
0.34
0.735
I.49
i-55
i-3
I.I3
1-25
o.54
0.265
0.385
o-575
1.08
0.825
o.77
0.78
1.02
0.67
400 365
watts watts
I.46
I.42
2.4
1.6
2.1
2.2
2.1
3-2
3-35
2.06
1-33
0.68
2.4
1.68
2-5
2.4
1-95
1.64
2.1
240
watts
o-935
0.85
1-55
1.1
1-57
1. 19
1.23
1.38
2.1
1. 21
43§ TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
TABLE XIV.— (Intensity Series.)
Showing the illumination measurements in foot-candles at nine representa-
tive stations for the different intensities used for the direct system (8 lamps).
Horizontal
Vertical
45°
Station
4 So
WilttS
320 | 200
watts j watts
120
watts
480
watts
320
watts
200
watts
120
watis
480
watts
320
watts
200
watts
120
watts
Card
12
16
3i
34
39
45
54
53
Average.
2.6
2.8
4-4
2.95
2.65
3-o
3-6
3-o
4.4
2.72
I.97
I.94
2.8
2.1
I.76
2.2
2.1
2.2
3-1
I.8l
16
36
2.4
i-34
1-3
1-25
1.2
1.22
2.1
'•13
O.64
O.69
1.22
O.7I
O.76
O.7
O.69
0.6S
1.3
0.68
I.02
0.45
O.4I
I.06
i-35
i-5
i-54
■•54
1.69
1.48
O.65
O.4I
O.36
O.7I
I. OI
I.O
I.07
I.I
1.22
O.99
0.45
0.2I
0.2
0.2S
0.92
O.66
0.72
o-59
o.77
0.62
0.32
0.15
O.I I
0.32
0.4
0.44
0.46
0.4
0.52
°-37
2.0
1-7
2.4
2-35
2.2
2.6
2-35
3-*
3-6
1. 12
1-39
1. 12
1 88
1-45
1-45
1.8
1.84
2.4
2-5
C.75
O.85
O.76
1.44
I.03
I.24
I.05
1- '5
1. 18
1.6S
0.47
0 45
O.41
0.66
0.6
0.56
O.65
0.65
I.63
O.96
0.28
TABLE XV.— (Intensity Series.)
Showing the brightness measurements in candlepower per square inch for
the different intensities used for the semi-indirect system at points indicated
by the letters A, B, C, D, etc., see Fig. 3, Further Experiments on the Effi-
ciency of the Eye, etc., Trans. I. E. S. (1915), vol. X, p. 452b.
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
X
Reading page horizontal .
Reading page 450 position
800 watts
0.6S7
0.0461
0.0858
0.0461
0.00264
0.0034
0.0058
0.00662
0.00638
0.00149
0.00462
0.00255
0.00572
O.002S6
0.00704
0.00616
0.003432
0.0107
0.00654
480 watts
0.370
0.0219
0.0504
0.0219
0.00177
0.001S7
0.00242
0.00259
0.00237
0.00076
0.00189
0.00173
0.00224
0.00173
0.00462
0.003196
0.00176
0.00462
0.00316
320 watts
O.180
o 01402
0.0346
0.0163
o 0008
0.001034
0.00187
0.00162
0.00187
O.C004S4
0.0014
0.0OI0S5
0.001408
0.001085
0.00264
0.00 1 9S
0.00105
0.0029
0.00193
o. 142S
0.01008
0.02414
0.0100S
0.00061
0.000792
0.00123
O.COI44
0.00123
0.000325
0.000902
0.00063
O.OOII
0.00063
0.00176
0.00154
0.000814
0.002024
0.00176
TABLE XVI.— (Intensity Series.)
Showing the brightness measurements in candlepower per square inch for
the different intensities used for the direct system (16 lamps) at points indi-
cated by ihe letters A, B, C, D, etc., see Fig. 2, Further Experiments on the
Efficiency of the Eye, etc., Trans, of the I. E. S., 1915, X. p. 452a.
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
x
Reading page horizontal . .
Reading page 450 position
400 watts
A 1000.00000
o. rSoj
0.002.53
0.00277
0.00097
0.00277
0.00303
0.00303
0.00316
0.00075
0.00252
0.00191
0.00273
0.00176
0.0026
0.00215
0.00184
0.00172
0.00396
0.0029
3*5 watts
IOOO.OOOOO
O.1232
0.00/51
o oor45
0.00067
0.00185
0.00246
0.00229
0.00216
0.0004
0.00167
0.00149
0.00198
0.00145
0.00242
0.00167
0.00103
0.00132
o 00405
0.00273
240 waits
IOOO.OOOOO
O. 1232
0.0015 I
O.OOII9
O.OOO545
O.OOI56
O.OOI72
O.OOI74
O.OOI8
O.OO0453
O.OOI76
O.OOI54
O.OOI94
O.OOI36
0.00143
o. 001 19
0.00103
0001
0.00211
0.00176
TABLE XVII. —(Intensity Series).
Showing the brightness measurements in candlepower per square inch for
the different intensities used for the direct system (8 lamps) at points indi"
cated by the letters A, B, C, D. etc., see Fig. 2, Further Tests for the Effr
ciencv of the Eve, etc., Trans, of the I. E. S., 1915, X, p. 452a.
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
X ••
Reading page hori
zontal
Reading page 45'
position
4S0 watts
IOOO.OOOOO
0.2953
0.00317
0.00454
o. 00 1 848
0.00198
0^0347
0.00391
0.00405
0.00069
o 00308
0.00229
0.00387
0.00192
0.00246
o 00192
0.00325
0.002376
0.00528
0.003696
320 watts
IOOO.OOOOO
0.2398
0.00299
0.0033
0.00118
0.00272
0.00361
0.00334
0.0029
0.00046
0.00167
0.00141
0.00229
0.00128
0.00252
0.00185
0.00222
0.00141
0.00334
0.0022
1000.00000
0.1657
0.00154
0.00185
0.00059
0.00145
0.00 r 89
0.00122
0.00167
0.00037
0.00122
0.00103
0.00141
0.00096
0.00101
0.00083
0.00136
0.000924
0.OJ229
0.00149
1000.00000
0.0S998
0.00097
0.000704
0.0003
o. 00063
0.00074
0.001 1
0.00092
0.00023
0.00073
0.00056
0.00068
0.00054
0.00065
0.00051
0.000704
o 00062
0.00123
0.00077
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FERREE AND RAND: EFFICIENCY OF THE EYE
445
Chart P.— Showing the effect on the efficiency of the eye of varying the
intensity of light for the semi-indirect system of lighting. Foot-candles at
the point of the test card are plotted along the abscissa; loss of efficiency
along the ordinate. X = points where the change in intensity was pro-
duced by changing the voltage (see Table XXI).
2 3 4 5 6 7
Chart F.
Chart G.— Showing the effect on the efficiency of the eye of varying the
intensity of light for the direct system of lighting. Foot-candles at the
point of the test card are plotted along the abscissa; and loss of efficiency
along the ordinate. A = curve for 16 lamps; B, for 8 lamps.
i
' — i
z
A,
3
c
>
I
i
i
y
5
Chart G.
446 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
The results of the tests for the intensity series are shown
in Tables XXI-XXIII. Three hours was ^elected as the period
of work in all of these experiments. Briefly stated the procedure
was as follows. First the most favorable intensity was deter-
mined and then variations were made on either side of this
intensity until it was certain that the characteristic effect of
increase and decrease of illumination was obtained. Table XXI
gives the results for Observer R under the semi-indirect system.
Seven variations of intensity were used. These results are typical
of the effect of variations of intensities for this system. Tables
XXII and XXIII show the results for the direct system for the
same observer. For the direct system the most favorable inten-
sity, it will be noted, was secured with the 8-lamp system with
a total wattage lower than could be gotten with the 16-lamp
system, i. e., a system totalling 200 watts caused the least loss of
efficiency to the eye, while 240 was the smallest total of wattage
that could be secured with the 16-lamp system.
Charts have been constructed also to give a graphic representa-
tion of these tables. Chart C shows the results of Table XXI ;
Chart D, of Table XXII ; and Chart E, of Table XXIII.
In these charts loss of efficiency was plotted against time of
work. In Charts F and G loss of efficiency is plotted against
intensity of light in foot-candles at the point of the test card.
Chart F shows the results for Table XXI ; Chart G for Tables
XXII and XXIII.
IV. CONCLUSION.
Two facts may be emphasized at this point. ( 1 ) Of the light-
ing factors that influence the welfare of the eye, those we have
grouped under the heading distribution are apparently funda-
mental. They seem to be the most important we have yet to deal
with in our search for the conditions that give us the minimum
loss of efficiency and the maximum comfort in seeing. If, for
example, the light is well distributed in the field of vision and
there are no extremes of surface brightness, our tests seem to
indicate that the eye, so far as the problem of lighting is con-
cerned, is practically independent of intensity. That is, when the
proper distribution effects are obtained, intensities high enough
to give maximum discrimination of detail may be employed
FERREE and rand: EFFICIENCY OF THE EYE 447
without causing appreciable damage or discomfort to the eye.
(2) For the kind of distribution effects given by reflectors of
the type employed in our direct and semi-indirect installations,
our results show that unquestionably too much light is being used
for the welfare of the eye.
Before concluding cur paper we wish again to state that the
units we have employed were not selected as fully representative
of the classes direct, semi-indirect, and indirect. Agreement in
fact has not yet been reached with regard to what falls within
each of these classes. The units employed were chosen rather
to show the effect on the ability of the eye to maintain its ef-
ficiency for a period of work of varying the factors we have
grouped under the heading distribution. We hope ultimately to
determine the limits between which each of these factors may vary
without damage to the eye in a selected range of lighting situa-
tions, especially the factor surface brightness. These most fav-
orable conditions will then serve as a goal to be attained what-
ever principle of lighting is employed.
Our next step in this division of the work will be to determine
the effect on loss in efficiency of using reflectors of different
degrees of opacity when the light is distributed to the plane of
work both by the direct and indirect principles of lighting.
That is, reflectors of different densities: prismatic, alba, opalux,
totally opaque, etc., will be used turned up and down. In each
case the installation will be made with special reference to giving
the best results obtainable for the particular type of unit em-
ployed; and the factors: evenness of illumination, diffuseness of
light, the angle at which the light falls on the work, and the
evenness of surface brightness will be varied separately in turn,
and the effect on loss of efficiency will be determined. More-
over, if it is found that the factors in question can not be studied
in sufficient detail in the concrete lighting situation, the work
will be supplemented by more abstract investigations. The re-
sults of this series of tests should give us among other things,
for example, a still better idea of what amount of brightness dif-
ference the eye is adapted to stand, and the comparative effect of
different ratios of surface brightness on loss of efficiency.
448 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
FURTHER EXPERIMENTS ON THE EFFICIENCY OF
THE EYE UNDER DIFFERENT CONDITIONS
OF LIGHTING.*
BY C. E. FERREE AND G. RAND.
Synopsis: This paper is a continuation of the papers presented to
the Society in 1912 and 1913. It describes the completion of the plan of
work outlined in the preceding papers for one set of lighting conditions
for three of the tests thus far devised by one of the writers (Ferree) —
namely, a test of the ability of the eye to hold its efficiency for a period
of work ; a test for loss of efficiency of the fixation muscles ; and a test
for the comparative tendency of different conditions of lighting to produce
discomfort. A report is also given of some miscellaneous experiments
related to the hygienic employment of the eye in which the following
points are taken up : the effect of varying the area and conversely the
intrinsic brightness of the ceiling spots above the reflectors of an indirect
system of lighting; the effect of varying the angle at which the light
falls on the work in a given lighting situation ; the effect of using an
opaque eye shade with dark and light linings with each of the installations
of artificial lighting employed in this and the previous work; the effect
on the efficiency of the fixation muscles of three hours of work under
these installations ; the effect of motion pictures on the eye for different
distances of the observer from the projection screen; a determination of
the tendency of different conditions of lighting to produce discomfort,
and a comparison of the tendency of these conditions to produce dis-
comfort and to cause loss of efficiency.
INTRODUCTION.
The present paper is the third in a series of papers presented
to this Society on the subject of lighting in its relation to the
eye. In the first paper of this series1 it was pointed out that if
we are to make a comparative study of the effect of different
conditions of lighting on the eye, we must have a means of
estimating effects. Work was described in this paper in which
* A paper read at the eighth annual convention of the Illuminating Engineering
Society, Cleveland, O., September 21-24, 1914.
The Illuminating Engineering Society is not responsible for the statements oj
opinions advanced by contributors.
1 Tests for the Efficiency of the Eye Under Different Systems of Illumination and
a Preliminary Study of the Causes of Discomfort, Trans. I. E. S., vol. VIII, 1913, pp. 40-60.
FERREE AND HAND: EFFICIENCY OF TIIK EYE 449
the tests already known to physiological optics had been applied
to the problem with negative results. New tests were proposed
and brief results were given to show their feasibility for the
problem in hand and to some extent their sensitivity. The sug-
gestion was made that a systematic investigation of the effect of
different conditions of lighting on the eye should include a study
of the following points: (1) the efficiency of the fresh eye, (2)
the loss of efficiency as the result of a period of work, and (3)
the tendency to produce discomfort. In the second paper of
the series,2 presented to the Society last year, a plan of work was
outlined and in part carried out in which the first two of the
above points were covered for a given set of lighting conditions.
The following factors of importance to the eye were enumerated :
the evenness of illumination, the diffuseness of light, the angle
at which the light falls on the object viewed, the evenness of
surface brightness, intensity and quality. The first four of these
factors are very closely interrelated and are apt to vary together
in a concrete lighting situation, although not in a 1 : 1 ratio. It
was convenient, therefore, for the purpose of this first investiga-
tion, which was primarily explorative in character, to group them
together under one heading and to refer to them as distribution
factors. In order to investigate the effect of certain wide varia-
tions in these factors, tests were conducted under four types of
lighting in common use: one was the lighting of a room by day-
light from windows ; the others were the lighting of the same
room by units commonly called direct, semi-indirect, and indirect,
selected to serve the purposes of the test.3
2 "The Efficiency of the Eye Under Different Conditions of Lighting — The Effect
of Varying the Distribution Factors and Intensity." Trans, of the 111. Eng. Soc,
1915, vol. X, pp. 407-447.
■ According to the plan as the investigation proceeds, the effect of varying each
of these factors separately will be studied. Xo especial attempt was made to do
this in the previous study. In making the experimental variations necessary to the
investigation, it was stated as our purpose to keep as close as possible to actual
lighting situations. More abstract investigations will be resorted to only when it
becomes necessary to supplement the results by details that cannot be gotten from
the concrete investigation. The objection to the abstract type of investigation, as
the writers see the case at the present time, is that its results are very apt to be
misleading. That is, what is permissible with regard to one factor in isolation, may
not be at all permissible in conjunction with other factors. A more feasible plan
seems to us to be to vary the factor over a certain practical range in actual concrete
situations. By a proper selection of the proper situations employed, the ground of
all that is practicable in lighting may be covered, and the results obtained can have
a safe application.
450 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
For the systems of artificial lighting the tests were made at
four positions in the room ; one at which six of the eight lighting
units employed were in the field of view, one at which four were
in the field of view, one at which two were in the field of view,
and one at which none was in the field of view. This variation
of position at which the observation was made accomplishes, it
was pointed out, two purposes. ( i ) It gives a more representa-
tive idea of the difference in the effect on the eye of the four
types of lighting employed. And (2) it shows the effect of
varying the number of surfaces in the field of view presenting
brightness differences, more particularly the number of primary
sources. The effect of varying intensity under each of the above
conditions of distribution was also tested. The two sets of ex-
periments were called respectively the distribution and intensity
series. Results were given in the preceding paper for only one
of the above positions in the distribution series, and for only the
direct and semi-indirect systems for the intensity series. The re-
sults of the remainder of these two series of experiments, to-
gether with the report of some miscellaneous experiments will
constitute the subject matter of the present paper. In these
miscellaneous experiments, the following points have been taken
up : the effect of varying the area and conversely the intrinsic
brightness of the ceiling spots above the reflectors for the indirect
system ; the effect of varying the angle at which the light falls on
the work ; the effect of using an eye shade with dark and light lin-
ings with each of the three installations of artificial lighting; the
effect on the efficiency of the fixation muscles of the eye of three
hours of work under each of the conditions of lighting described
in the distribution and intensity series ; the effect of motion
pictures on the eye for different distances of the observer from
the projection screen; a determination of the tendency of each
of the conditions of lighting that have been used in these ex-
periments to produce discomfort, and a comparison of the tend-
ency to produce discomfort and to cause loss of efficiency. Be-
sides including some additional matter, these experiments, in
connection with those of the preceding paper, complete the
plan of work we had outlined for one set of lighting conditions
for three of the tests we have thus far devised, namely, a test
FERREE AND RAND: EFFICIENCY Of THE EYE 451
for the ability of the eye to hold its efficiency for clear seeing
for a period of work, a test for loss of efficiency of the fixation
muscles, and a test for the comparative tendency of the different
conditions of lighting to produce discomfort, with the exception
that in a further analysis of the loss of efficiency caused by
these lighting conditions, which will be carried out in part by
means of these tests, data will be added later to show still more
clearly the relative amounts of loss that are sustained by the dif-
ferent functions of the visual apparatus.
DISTRIBUTION SERIES.
As was pointed out in the former paper, in order to get the
effect of variation in the distribution factors on the eye's loss of
efficiency as the result of a period of work, the test should be
conducted with the quality and intensity of light made as nearly
equal as possible. The quality of light was made approximately
the same for the three installations of artificial lighting employed
by using clear tungsten lamps in each case. It was decided to
make the intensity of light as nearly equal4 as possible at the
point of test, and to give a supplementary specification of the
lighting effects in the remainder of the room for the three in-
stallations of artificial light.
At the point of test the light was photometered5 in several
directions. It was made approximately equal in the plane of the
test card and as nearly as possible equal in the other directions.
The specification of the lighting effects in the remainder of the
room was accomplished as follows : ( I ) A determination was
made of the average illumination of the room under each of the
three installations. The room was laid out in 3-ft. (0.0 m.)
4 This equalization was made at the point of test for the position of the observer with
six of the fixtures in the field of view. For the other positions illumination measure-
ments were made in several directions at the test card, and brightness measurements
were made of the surface of the test card and of the observer's book held in the horizontal
and 45 deg. positions. Equalization could not have been made at all of these poinls with-
out having changed the relation and magnitude of the distribution factors, which would
not have been in accord with the purpose of the test, namely, to determine the effect of a
certain grouping or relation of these factors for the four positions in the room.
6 We have not as yet made the fuller photometric specifications of the room lighted by
daylight with our present arrangement of windows, curtains, etc. We hope to make the
effect of distribution factors in daylight illumination (employing windows, skylights,
etc.) the subject of a future study. In this study a photometric analysis of the illumina-
tion effects produced will be made an especial feature.
4
452 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
squares and illumination measurements were made at 66 of the
intersections of the sides of these squares. Readings were taken
in a plane 122 cm. above the floor with the receiving test plate
of the illuminometer in the horizontal, the 45 deg. and 90 deg.
positions measuring respectively the vertical, the 45 deg., and
horizontal components of illumination. The 122 cm. plane was
chosen because that was the height of the test object. (2) A
determination was made of the brightness of prominent objects
in the room, such as the test card, the reflectors for the semi-
indirect installation, the reading page, the specular reflection
from surfaces, etc. The brightness measurements were made by
means of a Sharp-Millar illuminometer with the receiving test
plate removed. The instrument was calibrated against a mag-
nesium oxide surface obtained by depositing the oxide from the
burning metal on a white card. By this method the reflecting
surfaces were used as detached test plates. The readings were
converted into candle-power per sq. in. by the following formula :
Brightness = Foot-candles/7r X 144-
(3) Photographs were made of the room from three positions
under each system of illumination.
A complete specification of the test room, the types of installa-
tion used, and the illumination effects produced for the systems
of lighting, is given in the previous paper which appears else-
where in this number of the Transactions (pp. 413-422). Only
such data will be repeated here as are necessary for reference.7
In Fig. 1 the test room is shown drawn to scale: plan of
room, north, south, east and west elevations. In the draw-
ing, plan of room, are shown the 66 stations at which the
illumination measurements were made, and the positions of
the outlets for the lighting fixtures, A, B, C, D, E, F, G, and H.
In the drawing, east elevation, the observer in position at one
of the points (Position I) at which the tests were taken is repre-
T For a description of the test see the previous article referred to above
(pp. 410-413); also Tests for the Efficiency of the Eye Under Different Systems of
Illumination and a Preliminary Study of the Causes of Discomfort, Trans. I. E. S.,
vol. VIII (1913). PP- 41-51-
ruw a udom
Fig. i. — Plan of test room.
Fig. 2.— Showing brightness measurements of all surfaces having very high or very
low brilliancj-, direct system. The brightness of the printed page from which the
observer read was, when held in the horizontal position, 0.0057 cp. per sq. in.; in
the 45 deg. position, 0.004 cp. per sq. in.';
6 The bright spots on the doors of the apparatus case rated at 100 cp. persq. in., shown
in Fig. 2. were not in the field of view when the tests were taken. That is, when the tests
were taken, the doors were thrown open, and all of the apparatus which might give
specular reflection was removed.
Fig. 3. — Showing brightness measurements of all surfaces having very high or very
low brilliancy, semi-indirect system. The brightness of the printed page from
which the observer read was, when held in the horizontal position, 0.005S cp. per
sq. in.: in the 45 deg. position, 0.0039 CP- Per scl- in-
Fig. 4.— Showing brightness measurements of all surfaces having very high or very
low brilliancy, indirect system. The brightness of the printed page from which
the observer read was. when held in the horizontal position, 0.00SS cp. per sq. in.:
in the 45 deg. position, 0.0043 cp. per sq. in.
FERREE AND RAND: EFFICIENCY OF THE EYE 453
sented.8 The other three positions are indicated in the photo-
graphs by (x). They will be referred to in the tables and charts,
in order, by the numerals II, III, and IV.
Table I shows the number and wattage of the lamps used at
the outlets A, B, C, D, E, F, G, and H ; and Table II shows the
illumination measurements for each of the 66 stations repre-
sented in Fig. I. These measurements were made with the re-
ceiving test plate of the photometer in the horizontal, vertical
and 45 deg. planes.9
8 The track along which the test card was moved was parallel to the east and
west walls of the room. During the three hours of reading which intervened be-
tween the two tests, the observer moved just far enough back from the upright sup-
porting the mouth-board to give room for the book to be held and to permit of a
comfortable reading position. The book was elevated and held approximately at an
angle of 45 deg. When taking the test, the observer faced the north wall of the
room, in such a position that with the eyes in the primary position, the lines of
regard were parallel with the east and west walls of the room. Care was taken to
have print of uniform size and distinctness for use with the three systems and to
have a page which gave a comparatively small amount of specular reflection.
8 See also Table III, The Efficiency of the Eye Under Different Conditions of
Lighting, etc., Trans. I. E. S., vol. X, 1915, p. 416a. This table was compiled as a
supplement to Table II for the purpose of making a comparative showing of the
evenness of illumination at the 122 cm. level given by the three systems of lighting.
Two cases were made of this. (1) Comparisons were made of each component from
station to station; (2) the difference between the components was compared. To
facilitate these comparisons (a) the mean variation from the average of each of the
components was computed; and (b) the difference between the averages of the three
components was determined. The evenness of the illumination, it will be remembered,
is not only of importance to the efficiency of the eye with reference to the object
directly viewed; but also in its influence on the distribution of surface brightness.
The evenness of surface brightness depends in general upon two sets of factors; (1)
the nature and position of the reflecting surfaces in the room; and (2) the type of
delivery of light to these surfaces.
We realize that the evenness of the illumination on the 122 cm. plane given by
the indirect and semi-indirect units was somewhat interfered with by the reflectors of
the direct system which were beneath and a little to the right of these units when in
position for the test. Also the evenness of surface brightness on the ceiling for the
direct system was interfered with by the indirect and semi-indirect reflectors which
were above and a little to the side of the direct units. The influence of this "dead
apparatus" will be eliminated in the next series of installations. Moreover, the in-
stallation in each case was not such as to give the best effects obtainable from the
type of reflector used. For example, the indirect reflectors were too close to the
ceiling to give the maximum evenness of illumination and surface brightness for
the type of reflector employed. The analysis of the effects given in the former paper
was not made, therefore, for the purpose of drawing general conclusions with regard
to the type of reflector used. It was made solely for the sake of the comparison of
the illumination effects obtained with the corresponding results for loss of efficiency.
454 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
TABLE I.
Showing the number and wattage of the lamps used at outlets
A, B, C, D, E, F, Gand H.
Outlet Direct Semi-indirect Indirect
Watts Watts Watts
A 2-6o I-IOO I-IOO
B 2-60 1-100 1-100
C 2-60 1-100 1-100
D 2-40 1-100 i-loo
E 2-60 1-100 1-100
F 2-60 1-100 1-100
G 2-60 1-100 1-100
H 2-40 1-60 1-100
TABLE 11.— Distribution Series.10
Showing the illumination measurements in foot-candles for each of the 66
stations represented in Fig. 1 for the direct, semi-indirect, and indirect
systems used.
Horizontal Vertical 45°
Semi- Semi- Semi-
Station Direct indirect. Indirect Direct indirect Indirect Direct indiiect Indirect
1 1. 41 I.44 1.22
2 I.32 I.47 I.26
3 I. IO I.40 I.32
4 1.37 i. 10 1.47
5 2.03 2.58 2.20
6 2.50 3.20 2.95
7 2.51 3.60 2.90
3 3-3° 3-75 3-oo
9 2.78 2.53 2.20
10 1.50 1.59 1.35
11 2.12 1.64 1.66
12 4.20 2.65 2.70 0.47 0.48 0.47 2.40 1.25 1.43
13 6.10 5.25 4.10 0.47 0.48 0.42 3.30 2.25 1.96
14 3.70 4.95 4.40 0.48 0.47 0.47 2.00 2.40 2.30
15 3.00 4.S5 4.50 0.44 0.48 0.47 i-97 1.8S 2.30
16 6.60 4.25 4.10 0.70 0.37 0.48 3.58 1.60 2.10
17 4.65 2.35 3.15 0.48 0.24 0.46 1.80 0.69 1.60
18 2.15 1.69 2.20 0.49 0.38 0.47 1. 10 0.66 1.63
19 2.95 2.10 2.50
20 5.30 3.20 3.40 1.62 0.53 0.86 3.00 2.30 2.20
21 6.60 4.80 4.60 2.00 0.71 0.94 3.60 1.85 3.00
22 2.25 4.40 4.80 0.61 0.69 1.07 1. 15 1.80 2.90
23 4.50 6.00 5.10 1.20 1. 14 1. 10 2.18 3.30 2.90
24 6.95 5.40 5.00 1.76 1.30 1.04 3.60 3.10 3.00
25 4-85 3-72 3-5o 1-33 o-78 0.75 2.75 1.85 2.10
26 2.50 1.82 2.20
27 2.81 2.05 2.40
28 6.50 3.28 3.70 1.30 1. 11 1. 12 4.40 2.10 2.50
29 9.00 6.40 5.20 1.45 1.50 1.48 6.30 3.60 3.40
30 4-95 6.95 5.40 1.36 1.46 1.40 3.15 4.15 3.60
31 4.80 6.20 5.20 0.77 1.20 1.24 2.78 3.85 3.60
FERREE AND RAND '. EFFICIENCY OF THE EYE
455
TABLE II.— Distribution Series. — (C
ontinue
d.)
Horizont
al
Vertical
45°
Semi-
Semi-
Semi-
Station
Direct
indirect
Indirect
Direct
indirect
Indirect
Direct
indirect
Indirect
32
9.20
5-50
5.00
O.47
0.2S
1-33
5.20
2.25
3-40
33
6.20
3-iS
3-70
1-54
0.75
1.22
4.60
I.83
2.6o
34
5-75
4-30
4.00
2.S5
I.20
1.46
4-3°
2.92
3.IO
35
8.00
6.90
5-4o
3-70
I.70
r-65
6.00
4.40
4.90
36
5.60
7-25
5-3o
2-35
1. 91
1.65
4.20
4.68
4.00
37
5-45
7.00
5.80
2.18
2-15
1.82
3-78
4-55
4.00
38
8.25
6. So
5-4o
3.60
2.20
1.72
6.00
4.60
3.8o
39
6-35
3-7o
4.00
2.8o
1.40
i-43
4.60
2.80
3.00
40
3.00
2.05
2.30
4i
2.70
i-73
2.10
42
7-3o
3-65
3-5o
2.50
1.64
1.36
5-4o
2-93
2.80
43
9.80
6.90
5. CO
2.70
2.0S
1.7S
7.20
4-50
3-9°
44
5-5o
7.10
5.20
2.42
2.IS
1. 88
4-35
.5.10
4-3°
45
5-45
8.00
5.20
2.60
2.00
i-93
4.80
5-30
4.20
46
10.00
7.70
5.20
2-75
1.90
1.86
8.00
5-4o
4.10
47
6.60
4.20
3.60
2-45
1.56
i-33
5-3°
3-05
2.90
48
5-8o
4-35
3-70
3.20
1.69
1.74
5.00
3.60
3-30
49
8.40
7.20
4.80
4-3°
2.55
2. 10
7 20
5-8o
4.00
50
5-5o
7.70
4.90
3-35
2.42
2.10
8.50
5 -So
4.10
5i
5-4o
6.80
5.00
3-05
2.68
2.15
4.60
5-35
4-35
52
8.00
6.40
4.70
4.20
2-55
i-93
6.50
4.82
4.00
53
6.60
3S5
3.60
3.00
1-77
1.41
5-°J
3.20
3.00
54
6.95
2.88
2. So
2.62
1.80
1.50
5.80
3.00
2.90
55
9.00
5-9o
390
3-15
2.40
1.94
S.00
5.20
3-75
56
4-95
5-9°
4.60
3.15
2.50
2.10
5-30
5-So
4.40
57
4-65
6.10
450
3.00
2.60
2.20
4-65
5-So
4.40
58
9-75
6-35
4.00
3-35
2.58
2.00
8.50
5-8o
4.00
59
5.85
3.20
2.90
2.98
1.90
1.76
5.60
3-62
3.10
60
3-85
2-57
2.60
1.66
2.90
61
5.20
4.20
3.10
4-45
2.60
1.90
7. So
5-4o
3-5°
62
3-3o
4.20
3.20
3-3°
2-95
2.10
4-95
5-7o
3-70
63
3-52
4.20
3.00
3.60
2.80
2.20
5.60
5.00
3-5o
64
5-4o
3-7o
3.10
4.60
2-45
i-93
7-65
4.60
3-4o
65
4-15
2.40
2.25
4.00
1.79
i-54
5-50
2.82
2.60
66
2.10
1.42
i-35
Average 5.0 4.27 3 .61
1.59 1.48 4.77 3.63 3.30
'" Reduced to equal wattages (Soo watts) these installations give the following average
illumination values in foot-caudles for the receiving test pbite 111 the positions specified
above : Direct system: horizontal, 4.54; vertical, 2.2; 450. 433. Semi-indirect system:
horizontal, 4.49; vertical, 1.67; 450, 3.S2. Indirect : horizontal, 3.61; vertical, 1.4S; 450, 3.3.
It may not be out of place to suggest here that a careful study of the illuminating effi-
ciencv of different types uf lighting units should be made under conditions that are strict-
ly comparable for a wide range of variation. Such tests should be made under common
supervision in a model room so constructed as readily to permit of the kind of variations
needed; and should be, if possible, paralleled by tests for the efficiency of the eye. In
working towards a reconstruction of lighting conditions, it is obvious that tests for the
efficiency of the eye and for illuminating efficiency should go haud in hand.
456 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Figs. 2, 3 and 4 are taken from the series of 9 photographs (see
Figs. 2-10, op. cit., pp. 4i6b-4i6d) showing the illumination effects
produced by the three systems of lighting. In these figures are
given the brightness measurements of all surfaces having very
high or very low brilliancy. The spot measured is indicated by a
cross and the numerical value of the brightness measurement in
candlepower per square inch is printed nearby. These spots are
also lettered for convenience of reference in the intensity series.
That is, since several installations were used in the intensity
series, it was found convenient to express these values in tabular
form and to identify them with the surfaces measured by means
of letters. These photographs were taken from a point in line
with the four positions of the observer as near to the south wall
of the room as was possible ; but owing to the narrow field of the
camera as compared with the binocular field, these views include,
for example, only about one-half of the field of vision of the
observer at the test station nearest to this wall of the room. The
camera's field in this position corresponds in fact very closely to
the field presented to the observer seated at the center of the
room. While, therefore, not all of his field of view for all of the
positions at which tests were made is covered by the brightness
measurements shown in the photographs, still the order of bright-
ness difference present in the field of view for the different sys-
tems is well represented by these measurements, as can be seen by
an inspection of the preceding photographs (see also Figs. 2-10,
op. cit., pp. 4i6b-4i6d) and from the descriptions of the installa-
tions used. In order to facilitate certain features of comparison
such as, for example, the evenness of surface brightness for each
system for all of the room; for all of the room but the sources of
light; and for all of the room but the sources and the spots
above the sources, the brightness measurements shown in Figs.
2, 3 and 4 are also given in tabular form. These measurements
and the letters identifying them with the surfaces measured, are
given in Table III. In making the comparison it should be noted
that the spots mentioned are not in all cases identical for the
three systems. That is, owing to the different effects produced
by the different reflectors, the same spots were not always con-
spicuously light or dark for the three systems. The letters, E,
FERREE AND RAND: EFFICIENCY OF THE EVE
457
F, G, etc., may then refer to entirely different spots in case of
the three systems.
TABLE III.— Distribution Series.
Showing the brightness measurements in candlepower per square inch for
the surfaces A, B, C, D., etc., see Figs. 2, 3 and 4.
Surface Direct Semi-indirect Indirect
measured system system system
A 1000.0000 O.710 0.138
B 0.3816 0.057 0.0715
C 0.517 0.093 0.066
D 0.010 °-°59 0.0022
E 0.00296 0.0029 0.0030
F 0.0044 0.0033 0.00123
G 0.0078 0.0053 0.0049
H 0.0077 0.006 0.0040
I 0.0075 0.0062 0.0042
J 0.0014 0.0010 0.00095
K 0.0063 0.0046 0.00255
L 0.0042 0.0027 0.00246
M 0.0065 0.0051 0.00352
N 0.0047 0.0027 0.00272
O 0.0074 0.0066 0.00343
P 0.006 0.00484 0.0030S
Q 0.00396 •
TABLE IV.— Distribution Series.
Showing the brightness measurements in candlepower persq. in. of the test
card, reading page horizontal, and reading page in the 45 deg. position for
Positions I, II, III, and IV, for the direct, semi-indirect, and indirect systems.
Position Direct Semi-indirect Indirect
of observer Surface measured system system system
I Test card 0.00308 0.0030 0.00299
Reading page horizontal 0.0057 0.0058 0.0088
Reading page 450 position- . . 0.004 0.0039 0.00431
II Test card 0.00506 0.00453 0.0046
Reading page horizontal 0.0088 0.0107 0.0088
Reading page 45° position- . • 0.0068 0.00726 0.00792
III Test card 0.0055 0.00462 0.00453
Reading page horizontal 0.0092 0.0087 0.00814
Reading page 450 position... 0.00704 0.0077 0.00594
IV Test card 0.0066 0.00475 0.00453
Reading page horizontal 0.00814 0.00572 0.00572
Reading page 450 position •• . 0.0063 0.00484 0.00484
In Table IV are given the brightness measurements in candle-
power per square inch for the test card and the reading page for
the four positions of the observer : I, II, III and IV, for the
direct, semi-indirect and indirect systems. The measurements of
the reading page were taken at the point of work for the four
positions of the observer with the book in the horizontal and 45
deg. position. During work the book was held in the 45 deg.
position.
In Tables V and VI are shown some prominent ratios of sur-
458 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
face brightness for the three systems.11 (See also Table VIII,
op. cit., p. 421. )12
In compiling these ratios it has been considered important to
make a comparative showine for the three systems (a) of the
extremes of surface brightness ; and (b) of the relation of the
brilliancy of objects in the surrounding field to the surface bright-
ness at the point of work. The extremes of surface brightness
11 In attempting to make comparisons of the effect of the different magnitudes of
brightness ratios, one obviously must bear in mind that the surfaces between which
the ratios are established are not in all cases in the same position in the field of
vision for the three systems. For example, the brightest surfaces in case of the
indirect system, namely, the spots on the ceiling directly above the reflectors, are
farther removed from the direct line of vision of the observer in the working position
than were the brightest surfaces in case of the direct and semi-indirect systems.
The position of the surface in the field of vision would come into question, for ex-
ample, in making a determination of the maximum va'ue of brightness difference the
eye is adapted to stand. While we have done a great deal of work on the effect nf
position of the brilliant surface in the field of vision in our investigation of the
causes of discomfort, we have made no especial investigation of this point in re'ation
to loss of efficiency. Doubtless what we shall all have to bear in mind is that, even
in the end, we cannot hope to specify narrowly what is most favorable, etc. In
lighting conditions. The factors that enter into the concrete lighting situation are so
complex or rather are so variable and so rarely duplicated that we can hope to make
general specifications with regard to what is most favorable, for example, only within
very broad limits. If one wishes to work the conditions down to a finer point than
this, the particular installation must be tested in situ. We are at present working
on a test which we hope will serve this purpose better than the test which has been
used in the work described in the preceding papers.
12 Table VIII, (op. cit., p. 421) was compiled from Tables IV-VII of that
paper to show the mean variation in surface brightness for all the surfaces measured
for the direct, semi-indirect, and indirect systems. In referring back to that paper
it may not be out of place to call to mind again that the percentages given in Table
VIII seem to indicate that the great advantage of the indirect over the other systems
of lighting we have used with regard to the factor, evenness of surface brightness,
comes, primarily at least, from its provisions for shielding the eye from the light
source rather than from any conspicuously greater evenness of illumination given
by it to the objects in the field of view. In fact, as may be seen from that table, all
the systems give a fairly even distribution of surface brightness outside of the
source and the surfaces immediately surrounding it.
The need of keeping surface brightness within certain limits and the primary im-
portance of properly shielding the eye from the source, to the accomplishment of this
desideratum, are obvious. Doubt' ess many ways will be devised in course of time for
cutting down useless and harmful brightness differences in lighting effects. For exam-
ple, the possibility is here suggested of producing a still smaller brightness difference
than is given by the indirect reflectors of the type we have employed, by using semi-
iidirect reflectors of such a density as to give a surface brilliancy equal to that of
the spot of light cast upon the ceiling. The value of this brilliancy, because of the
larger area of luminous surface presented, could then be made smaller than that of
the ceiling spot cast by the indirect reflector and still give the same amount of light
to the room. A similar effect may be obtained with the indirect reflector by using
lamps of lesser wattage and adding the light needed to make up the deficiency by
installing directly beneath the reflector lamps of low wattage in trans'ueent en-
closures of a density that gives a surface brilliancy equal to that of the ceiling spots.
The effect of both of these devices would be to lower the surface brilliancy for a
given light flux by increasing the area of the luminous surface. Whether either de-
vice would be advisable from other standpoints we are not at present prepared to
say.
i-KKRiiE and rand: EFFICIENCY of the EYE 459
are shown by giving the ratios between surfaces of the first,
second, third, etc., order of brilliancy and the surface of the
lowest order of brilliancy ; and the comparison of the brilliancy
of objects in the surrounding field to the brightness at the point
of work by giving the ratios of the surfaces of the first, second,
and third order of brilliancy to the brightness of the test card
and the reading page in the working position. The following
points may be noted, (i) The illumination effects produced by
the direct system are characterized by great extremes of surface
brightness, and a high ratio of brilliancy of objects in the sur-
rounding field to the surface brightness at the point of work.
These effects are much less pronounced for the semi-indirect sys-
tem and still less for the indirect. (2) A comparison of this
table with the tables giving loss of efficiency as the result of work
shows that while the extremes of surface brightness are enor-
mously larger for the direct than for the semi-indirect system,
the eye loses almost as much in efficiency for three hours of work
under the semi-indirect as under the direct system. That is, the
greatest ratio of brightness for the direct system is over one
thousand times as much as the greatest ratio for the semi-indirect,
while the difference in loss of efficiency for the two systems is
comparatively insignificant. On the other hand, the greatest
ratio of brightness for the semi-indirect system is only about five
times as much as for the indirect; while the difference in loss of
efficiency for three hours of work is very large, this loss of effi-
ciency for three hours of work for the indirect system being, it
will be noted, very small indeed. This seems to indicate (a) that
for the scale of brightness magnitudes and the illumina-
tion effects present in this series of experiments the gradation
of surface brightness for the indirect system is very close
to what the eye is adapted to stand without loss of efficiency ;
and (b) that an increase in difference in brightness above
this point is followed at first by a rapid increase in loss of
efficiency and later by a much slower increase. In the intensity
series, in the work of the former paper, it wrill be remembered,
the following points also came out. (1) The effect of size of
ratio on loss of efficiency is different for different orders of mag-
nitude of brightness. And (2) the size of the brilliant object, as
460 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
well as its brilliancy, is of importance. That is, within certain
limits, as yet undefined, an increase in the area of the brilliant
surface causes an increase in loss of efficiency.
In Table V the ratios were compiled from measurements show-
ing the extremes of brightness of prominent surfaces in the room.
In Table VI they were compiled to show the relation of the
brilliancy of objects in the surrounding field to the surface bright-
ness at the point of work for the positions of the observer, I, II,
III and IV13 (see Fig. i, p. 452a). In general a falling off in
the magnitude of brightness differences in the field of view
will be noted in order from the Positions I to IV. This
falling off is greatest for the direct system, next greatest for the
semi-indirect, and least for the indirect. Thus there is not only
a decrease in the number of surfaces in the field of view show-
ing a high brilliancy from Positions I to IV, but also a decrease
in the magnitude of brightness difference between the surfaces
of high brilliancy and the test card, between these surfaces and
the reading page, etc., especially for the direct and semi-indirect
systems. An inspection of the table for loss of efficiency shows,
roughly speaking, a correspondingly marked decrease in loss of
efficiency from Positions I to IV for the systems which show the
marked decrease in brightness difference, that is, for the direct
and semi-indirect systems. The decrease in loss of efficiency,
it will be noted, is practically nothing for the indirect system.
Thus not only much less loss of efficiency is sustained by the
eye for the indirect units used, but the results are much more
independent of the position of the observer in the room.
The loss of efficiency for the Positions I, II, III and IV for the
three systems is shown in Table VII.14
13 It may also be of interest to the reader to work out for these four positions the
ratios: lightest to darkest, darkest to test card, darkest to reading page, etc.
14 Obviously in the consideration of the effect of a given lighting situation on
the ability of the eye to hold its efficiency for a period of work, the age of the ob-
server and the condition of his eyes should be taken into account. All the observers
that have been employed by us in this work were .under 26 years of age. Following
is a clinic report of the eyes of the observer whose results are given in the following
table, made by Dr. Wm. Campbell Posey of Philadelphia.
Observer R.
With glasses. — Vision of right eye = 20/25. Par muscle test = Q 14 esophoria.
Vision of left eye = 2o'2o. Near muscle test = orthophoria.
Ophthalmoscopic examination.- — Right eye = mixed astigmatism, Yi diopter.
Left eye = hyperopic astigmatism, 1 Yi diopters.
( Conthi ued on next page. )
FERREE AND RAND: EFFICIENCY OF THE EVE 461
Chart I gives a graphic representation of the results of this
table. Loss of efficiency is plotted along the ordinate and time
of work along the abscissa. Each of the large squares along the
abscissa represents an hour of work and along the ordinate an
integer of the ratio, time clear to time blurred. The effect on
loss of efficiency of the number and magnitude of brightness of
surfaces of high brilliancy, especially of primary sources, in the
field of view is obvious from these charts. The chart for position
IV, however, shows that there is still a considerable difference in
the loss of efficiency produced by the three systems, even when
there are no sources or other surfaces of high brilliancy in the field
of view. The indirect system still gives the least loss of efficiency,
the semi-indirect next, and the direct the most. As may be seen
in Figs. 2, 3, and 4, and in Tables III and VI there was little dif-
ference in the evenness of surface brightness in the field of view
presented to the observer in this position, certainly none that could
be considered of consequence in favor of the indirect system. The
above results seem to indicate, therefore, that while the evenness of
surface brightness is an important factor it is not the only factor
in a lighting situation which may influence the amount of loss of
efficiency sustained by the eye as the result of a period of work
We wish to repeat in this paper what was very strongly empha-
sized in our former paper, namely, that the units we have em-
ployed were not selected as fully representative of the classes
direct, semi-indirect, and indirect. Agreement in fact has not yet
been reached with regard to what falls within each of these
Externa! condition. — Adduction good; eyes slightly divergent under cover; cornea
clear; pupils, 2^ mm.; irides respond equally and freely to
light, accommodation, and convergence stimuli.
Glasses worn during test. — Right eye = — S., 0.50 D. ; — C, 0.37D., x ieo*
Left eye = — C, 0.50 D., x 1800
Lest the former paper has not appeared in print before this one is presented it
may be well to make some mention here also of the reproducibility of results that
may be obtained for our test for loss of efficiency. The mean variation of the ratio,
time clear to time blurred for the same observer working under conditions as nearly
constant as possible, is very small indeed. The order of magnitude of the mean
variation of the test for the fresh eye was obtained as follows. Beginning at 9 a. m.
five 3 minute tests were run with a rest period of 20 minutes between each test
This was done with all observers on several days under each system of lighting em-
ployed. The rest period was taken in each case in a room lighted by daylight, with
the observer facing a wall with an evenly lighted matt surface. For a single series
of five tests the variation in the time seen clear in the 3 minute periods have
always fallen within 1 per cent, for all of the observers we have used and for all
systems of lighting.
462 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
classes. The units employed were chosen rather to show the
effect of varying the factors we have grouped under the heading
of distribution on the ability of the eye to maintain its efficiency
for a period of work. We hope ultimately to determine the
CHART I.— Distribution- Series.
Showing the effect on loss of efficiency of varying the observer's position in
the room, or the number of bright sources, primary and secondary, in the
field of vision.
POSITION I
^liUSHi FIXTURES IN FIELD Of m!0«
POSITION II
POSITION III
POSITION IV
limits between which each of these factors may vary in a se-
lected range of lighting situations, without damage to the eye, es-
pecially the factor surface brightness. These most favorable
conditions will then serve as a goal to be attained whatever prin-
cipal of lighting is employed.
FERREE AND RAND: EFFICIENCY OF THE EYE
463
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466 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
As was also stated in our former paper our next step in this
division of the work will be to determine by using reflectors of
different degrees of opacity the effect on loss of efficiency when
the light is distributed to the plane of work both by the direct
and indirect principles of lighting. That is, reflectors of differ-
ent densities : prismatic, alba, opal lux, totally opaque, etc., will be
used turned up and down. In each case the installation will be
made with special reference to giving the best results obtainable
for the particular type of unit employed ; and the factors : even-
ness of illumination, diffuseness of light, the angle at which the
light falls on the work, and the evenness of surface brightness,
will be varied separately in turn and the effect on loss of effi-
ciency will be determined. Moreover, if it is found that the
factors in question cannot be studied in sufficient detail in the
concrete lighting situation, the work will be supplemented by
more abstract investigations. The results of this series of tests
should give us among other things, for example, a still better
idea of what amount of brightness difference the eye is adapted
to stand, and the comparative effect of different ratios of surface
brightness on loss of efficiency.
INTENSITY SERIES.
In the work of the preceding paper we had undertaken to
determine the most favorable intensities for the three types of
artificial lighting we had used in the distribution series, and the
effect of varying intensity with the particular grouping of distri-
bution factors represented in each case. As was stated in the
introduction of the present paper, this work was completed for
the direct and semi-indirect systems but not for the indirect. For
the semi-indirect installation it will be remembered that the eye
fell off heavily in efficiency for all intensities with the exception
of a very narrow range on either side of 2.2 foot-candles, meas-
ured at the point of work with the receiving test plate of the
photometer in the horizontal plane. For the direct installation
no intensity could be found for which the eye did not lose a great
deal in efficiency as the result of work. For the indirect installa-
tion, however, as the following data will show, a comparatively
wide range of intensity may be used without the eye suffering
FERREE AND RAND: EFFICIENCY OF THE KYI- 467
any considerable loss of efficiency as the result of three hours of
continuous work.
The tests were made in the same room, with the same fixtures,
and in general, with the same conditions of installation and
methods of working as were described in the work on the distri-
bution factors. To secure the various degrees of intensity needed,
lamps of different wattage were employed. These were selected
from a series of tungsten lamps ranging from 15 to 100 watts. In
order to keep the distribution factors as nearly constant as pos-
sible for a given type of system, the lamps used in making the
test for that type of system were all of one wattage, *. e., were
all 15's, 25's, 40's, 6o's or ioo's.
For the indirect system the total range of intensity employed
is shown by the following figures. The series was begun with
25-watt lamps, and consisted of 25, 40, 60, and 100-watt lamps.
For the 25 watt lamps the photometer reading at the point of
work with the receiving test plate in the horizontal plane showed
1.33 foot-candles of light; with the receiving test plate in the
vertical plane, 0.39 foot-candle ; and with the receiving test plate
in the 45 deg. plane, 0.87 foot-candle. For the 100-watt lamps 5.2
foot-candles were obtained with the receiving test plate in the
horizontal plane; 1.36 foot-candles with the test plate vertical;
and 3.5 foot-candles with the test plate inclined 45 deg. The tests
for loss of efficiency15 showed probably a slight advantage for the
25-watt lamps, although the difference in result for the different
intensities is sufficiently near in value to the mean variation of
the test as to be scarcely worthy of consideration.
As was the case for the direct and semi-indirect installations,
the following specification was made of the illumination effects
produced by the indirect installation. ( 1 ) Illumination measure-
15 In conducting these tests it was found necessary to allow a period of adaptation
without work, to the illumination of the room before the first test was taken. If this
were not done, especially in case of the lower intensities of lights used, the changing
sensitivity of the eye to the intensity of light employed, produced a noticeable change
in the visual acuity between the times the tests before and after work were taken.
Since the distance of the test card was kept the same for the two tests, this change in
the visual acuity tended to influence the ratio, time clear to time blurred. To deter-
mine the length of time needed under a given intensity of light to insure a constant
acuity, so far as adaptation is concerned, preliminary tests were made as follows.
The acuity of the observer was taken every 3 minutes until no noticeable change
was found. This length of time was then always allowed for that observer as an
adaptation period prior to the loss of efficiency test conducted for the given intensity
of illumination.
5
468 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY'
ments were made for the highest intensity employed at the 66
stations in the test room. These measurements were made in
the way described in the preceding section. For the other in-
tensities used, measurements were made at nine representative
stations to show in a general way the order of magnitude of
reduction produced by using the lamps of lower wattage. (2)
Brightness measurements were made of the prominent objects
in the room, such as :he test card, the book of the observer, and
all surfaces showing very high or very low brilliancy for all of
the intensities.
In Table VIII are given the illumination measurements at the
66 stations for the highest wattages used, made with the re-
ceiving test plate of the photometer in the horizontal, vertical,
and 45 deg. planes. Tables IX and X show the illumination meas-
urements at the nine representative stations for the other watt-
ages employed in the series. The order of magnitude of reduc-
tion of the illumination of the room produced by using the lamps
of lower wattage conforms pretty closely in each case, it will be
observed, to the simple ratio of the wattages employed. (See
foot-note to Table XII, p. 472.) As was the case for the semi-
indirect system, noted in the preceding paper, socket extenders
had to be used with the 25 and 40-watt lamps. That is, without
the extenders these lamps, owing to their smaller size, came so low
in the reflector as to change the distribution effects given by
reflectors. For example, without the socket extenders for these
shorter lamps, the spot of light on the ceiling was made smaller
and correspondingly more brilliant. It was thought advisable to
determine whether this comparatively small change in illumina-
tion effects would cause any difference in the eye's ability to hold
its efficiency for a period of work. In the specification of illumi-
nating effects, therefore, measurements have been made for the
25 and 40-watt lamps both with and without socket extenders.
In Table IX illumination measurements for the 25 and 40-watt
lamps are given with socket extenders, and in Table X illumina-
tion measurements for these lamps are given without socket
extenders. In Table XI are given the brightness measurements
for the indirect installation for the different intensities used, both
with and without socket extenders for the 25 and 40-watt lamps.
FERREE AND RAND: EFFICIENCY OF THE EYE
469
The points at which the measurements were taken are indicated
by the letters A, B, C, D, E, F, etc., see Fig. 4, p. 452b. In Table
XII are given the prominent brightness ratios for the different
intensities used. Obviously an important point of comparison
for the purposes of this investigation is the ratios with and with-
out socket extenders for the 25 and 40-watt lamps.
TABLE VIII.— Intensity Series.
Showing the illumination measurements in foot-candles for each of the 66
stations represented in Fig. 1 for the indirect system used.
tatiot
» Horizontal
Vertical
45°
Station
Horizontal
Vertical
45°
I
1.22
—
—
34
4.0
I.46
3-i
2
1.26
—
—
35
5-4
1-65
4-9
3
1-32
—
—
36
5-3
I.65
4.0
4
1.47
—
—
37
5-8
I.82
4.0
5
2.2
—
38
5-4
I.72
3-8
6
2-95
—
—
39
4.0
1-43
3-o
7
2.9
—
—
40
2-3
—
—
8
3-0
—
—
4i
2.1
—
—
9
2.2
—
—
42
3-5
1.36
2.8
10
1-35
—
—
43
5-o
1.78
3-9
11
1.66
—
—
44
5-2
1.88
4-3
12
2.7
O.47
1-43
45
5-2
i-93
4.2
13
4-1
O.42
1.96
46
5-2
1.86
4-i
14
4-4
0.47
2-3
47
3-6
1-33
2-9
15
4-5
O.47
2-3
48
3-7
1.74
3-3
16
4-1
O.48
2.1
49
4-8
2.1
4.0
17
3-15
O.46
1.6
50
4-9
2.1
4.1
18
2.2
O.47
1.63
5i
5o
2.15
4-35
19
2.5
—
—
52
4-7
i-93
4.0
20
3-4
O.86
2.2
53
3-6
1.41
3°
21
4.6
0.94
3-°
54
2.8
i-5
2.9
22
4-8
I.07
2.9
55
3-9
1.94
3-75
23
5-i
1. 1
2.9
56
4.6
2.1
4.4
24
5-o
I.04
3-o
57
4-5
2.2
4.4
25
3-5
0-75
2.1
58
4.0
2.0
4.0
26
2.2
—
—
59
2-9
1.76
3-i
27
2.4
—
—
60
2.6
1.66
2.9
28
3-7
1. 12
2.5
61
3-i
i-9
3-5
29
5-2
I.48
3-4
62
3-2
2.1
3-7
30
5-4
i-4
3-6
63
3-o
2.2
3-5
3i
5-2
1.24
3-6
64
3-1
i-93
3-4
32
5-o
i-33
3-4
65
2.25
i-54
2.6
33
3-7
1.22
2.6
66
i-35
—
—
Average 3.61
1.48
3-3
4/0 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
TABLE IX. — Intensity Series.
Showing the illumination measurements in foot-candles at nine repre-
sentative stations for the different intensities used for the indirect system.
Socket extenders used with the 40 and 25-watt lamps.
Station
Horizontal
Vertical
45°
800
4S0 320
200
800
480
320
200
800
480
320
200
Card
5-2
3.0 1.7
1-33
1.36
O.765
O.49
039
3-5
i-97
1.08
0.87
12
2.7
I.63 O.97
0.65
0.47
0.265
0.18
O.I2
1-43
0.83
0.48
0.44
16
4.1
2.2 I.32
1. 11
0.52
0-33
O.24
O.14
2. 1
1.22
0.66
0.6
3t
5-2
2.7 I.84
i-45
1.24
0.77
O.51
0.47
3-6
1-95
1. 16
1. 01
34
4.0
2.25 1. 21
1.0
1.46
0.79
O.52
O.49
3-1
1.63
0.89
0.78
39
4.0
2.2 1.6
0.83
1-43
O.725
O.51
0.37
30
1-57
1.04
0.64
45
5-2
2-75 i-94
1.28
i-93
O.99
O.58
0.53
4.2
2.18
1-43
1.0
54
2.8
1.48 I. 16
0.68
i-5
0.82
0.63
O.41
2.9
I.5I
1.23
0.68
58
4.0
2.1 I.3
1.09
2.0
O.94
O.64
O.52
4.0
2.2
i-3
0.98
Ave.
3.61
2.l6 I.44
0.9
1.32
0.S9
0.59
0.37
3-3
1.98
1.32
0.83
TABLE X.— Intensity Series.
Showing the illumination measurements in foot-candles at nine represen-
tative stations for the different intensities used for the indirect system. No
socket extenders used with the 40 and 25-watt lamps.
Station
Horizontal
Vertical
45°
* ■
800
480 320
200
800
480
320
200
800
480
320
200
Card
5-2
3.0 I.48
I. 16
1.36
O.765
0.407
0.37
3-5
1.97
o.95
0.76
12
2.7
I.63 O.84
0.5
0.47
0.265
O.I39
O.99
1-43
0.83
o.44
0.282
16
4.1
2.2 I. OI
O.96
0.52
0.33
O.143
O.14
2.1
1.22
0.5
0.48
3i
5-2
2.7 I.48
1-3
1.24
0.77
O.462
0-39
3-6
1-95
1.0
0.86
34
4.0
2.25 O.99
1.0
1.46
0.79
0.5
0.45
3-i
I.63
0.84
0.8
39
4.0
2.2 I.63
0.78
1-43
o.725
0.44
O.36
3-o
1-57
0.98
0.6
45
5-2
2.75 1.62
1. 18
i-93
0.99
O.52
0.48
4.2
2.18
i-3i
0.98
54
2.8
I.48 I.03
0.63
i-5
0.82
0.61
O.41
2-9
I.5I
1. 18
0.65
58
4.0
2.1 I. II
0.87
2.0
O.94
0.54
0.42
4.0
2.2
1. 11
0.83
The results of the tests for the intensity series for the indirect
system are given in Table XIII. Three hours was selected as the
period of work in all of these experiments. The tests were taken
only as Position I (see Fig. 1, p. 452a), the position, it will be re-
membered, at which six of the fixtures were in the field of view.
It will be noted that there is practically no difference in the loss
of efficiency of the eye for the different intensities of illumination
when socket extenders were used for the shorter lamps. When
socket extenders were not used for these lamps, quite a little loss
of efficiency was experienced. This loss, moreover, was consider-
ably greater for the shorter 25-watt lamps than for the 40-watt
FERREE AND RAND: EFFICIENCY OF THE EYE
471
lamps. Since the prominent variable in this case was intrinsic
brilliancy of the ceiling spot above the reflector, the increased loss
of efficiency can probably be ascribed primarily to this cause; or
more comprehensively stated perhaps, to the change in the magni-
tude of the brightness differences that were present in the field of
vision. For example, the ratio, lightest to darkest for the 100-
watt lamps was 145; it was 133 for the 60-watt lamps; 142 for
the 40- watt lamps with socket extenders; and 135 for the 25-
watt lamps with socket extenders. For the 40-watt lamps with-
out socket extenders, however, this ratio was raised to 326, and
for the 25-watt lamps without socket extenders it was raised to
374. Similar changes were also made in the other ratios : lightest
to test card, lightest to reading page, etc., as may be seen by in-
specting Table XII.
TABLE XI.— Intensity Series.
Showing the brightness measurements in candlepower per square inch
for the different intensities used for the indirect system at points indicated
by the letters A, B, C, D, etc., see Fig. 4.
320 watts 200 watts
With Without With Without
Surface 800 480 socket ex- socket ex- socket ex- socket ex-
measured watts watts tenders tenders tenders tenders
A O.138 0.0704 O.0539 O.088 O.0352 0.0748
B 0.0715 0.0385 O.0252 0.0231 0.0165 0.0187
C 0.066 0.0352 0.0244 0.022 0.0159 0.0165
D 0.0022 0.00097 0.00079 0.00059 0.00064 0.0004
E 0.0030 0.000163 o. 001 19 0.0007 0.000S4 0.00057
F 0.00123 0.000401 0.00035 0.00022 0.00032 0.00018
G 0.0049 0.00169 0.00145 0.00101 0.00128 0.00084
H 0.0040 0.00163 0.00129 0.00092 0.0011 0.00072
I 0.0042 0.00158 0.00127 0.0009 0.0011 0.00068
J 0.00095 0.00053 0.00038 0.00027 0.00026 0.0002
K o. 00255 0.00123 0.00088 0.00088 0.00074 0.00064
L 0.00246 0.0012 1 0.00085 0.00079 0.00066 0.00046
M 0.00352 0.00158 0.00106 0.00097 0.00052 0.0007
N 0.00272 0.00101 0.00076 0.00061 0.00066 0.00044
0 0.00343 0.00128 0.00076 0.00028 0.00055 0.00019
P j. 00308, o. 001 19 0.00067 0.00027 0.00041 0.00018
X 0.00299 0.00154 0.00109 0.0008 0.00074 0.00059
Reading page
horizontal ..0.008S 0.00405 0.00281 0.0022 0.00198 0.0016
Reading page
450 position 0.00431 0.00273 0.00167 0.00154 0.00117 0.0009
472 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
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FERREE AND RAND: EFFICIENCY OF THE EVE
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FERREE AND RAND: EFFICIENCY OF THE EYE
475
A graphic representation of the results for the indirect sys-
tem with socket extenders is given in Chart II. In this chart
loss of efficiency is plotted against time of work in the manner
described in the preceding section. For the sake of comparison
results are shown also on this chart for the direct and semi-
indirect systems. A graphic representation has further been
made of the results for the indirect system with and without
socket extenders. This is shown in Chart III.
CHART III. -Intensity Series.
Showing the effect on loss of efficiency of changing the height of the light
source in the reflector of the indirect lighting fixtures. The effect on surface
brightness is primarily to change the area and surface brilliancy of the spot of
light thrown on the ceiling. Chart A shows the results when height of
source in the reflector is changed; Chart B, the results when the height is
kept approximately constant.
CHART A
CHARTB
1,25 WATTS
j^—— t en .
/
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40 •
0
J
3 4
EYE SHADE SERIES.
This series of experiments has been conducted for the follow-
ing reasons, (i) In general two methods are used to protect
the eye from the source of light, eye shades and lamp shades.
It is desirable to know whether the eye is protected equally well
by both; and if the eye shade can be substituted for the lamp
shade, what type of shade would best serve the purpose. (2)
And the statement has been made to us many times that with an
eye shade the three systems of artificial lighting we have used
should give equally good results : and results, moreover, as good
4/6 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
as those given by the indirect system without an eye shade.
There are in general two classes of eye shades, the translucent
and opaque. Up to this time we have confined our work to the
opaque shade. So far as we know it is customary to make the
opaque shade with a dark lining. This kind of lining is em-
ployed probably because of some notion that it is restful to the
eye to darken as much of the field of vision as is possible.18
The tests were begun with the opaque shade with the dark
lining. What we found as the result of these tests was somewhat
in contradiction to the predictions that had been made. The
shade did give pretty nearly the same results for the three sys-
tems ; but it did this, contrary to prediction, by improving the
direct and semi-indirect systems and making worse by almost
an equal amount the indirect system. That is, protected by the
opaque shade, the eye lost in efficiency for the three systems by
an amount somewhere near the mean of the losses experienced
by it for the three systems without a shade. Nor is this result
surprising when one reflects upon the conditions imposed upon
the eye by an opaque shade with a dark lining. While it pro-
tects the eye from the sources of light, such a shade does not by
any means eliminate harmful brightness differences in the field
of vision. It in fact creates for the eye a very unnatural bright-
ness relation, i. e., it renders the whole upper half of the field of
vision dark in sharp contrast with the brightly lighted lower
half. The direct effect of this is a strong brightness induction
C physiological) over the lower half of the field of vision which
manifests itself to the observer by causing glare in surfaces that
have no glare, and by increasing the glare in surfaces in which
glare is already present. This, it is scarcely necessary to point
out, operates against the discrimination of detail and puts the
eye under strain to see its objects clearly. Moreover, the unusual
and strongly irregular character of the image formed on the ret-
ina probably also sets up a warfare in the incentives given to
the muscles which adjust the eye. That is, the upper half of
the field of vision is dark and presents no detail. The effect of
this is probably to exert a tendency to cause the muscular relax-
18 Another popular view might be, so far as protection to the eye is concerned, to re-
gard the opaque eye shade as the analogue of the opaque or perhaps the indirect lamp
reflector and the translucent shade as the analogue of the semi-indirect reflector.
FERREE AND RAND: EFFICIENCY OF THE EVE 4/7
ation characteristic of the darkened field of vision. The lower
half of the field is light and filled with detail. The incentive
here is towards the best possible adjustment of the eye for the
discrimination of detail in the objects viewed, while the rim
of the shade, the sharply marked boundary between the dark and
light halves of the field of vision and much nearer to the eye
than the objects viewed,19 serves as a constant and consciously
annoying distraction to fixation and accommodation. These
complex and somewhat contradictory impulses given to the mus-
cles of the eye might very well, and doubtless do cause an exces-
sive and unnatural loss of energy and efficiency in case of the
prolonged adjustment of the eye needed for a period of work.
Early in the course of the tests it occurred to us that we might
render the brightness distribution in the field of view presented
to the eye wearing a shade more natural, and thereby improve
the effect of the shade on the eye, by employing a white instead
of a dark lining. By using a matt white paper20 with a reflection
coefficient of about 75 per cent, for this lining, the following
effects were produced. The two halves of the field of vision
were rendered much more nearly of equal brightness ; the glare
in the lower half of the field of vision was very noticeably
lessened and the discrimination of detail was correspondingly
improved; the upper half of the field of view no longer tended
to give to the eye the reflexes of the darkened field of vision;
and the rim of the shade did not stand out nearly so distinctly
in the field of view to distract accommodation and fixation. The
results of the test for loss of efficiency show, moreover, that our
surmise with regard to the effect of this change on the eye was
correct. The action of the white lining was greatly to improve
the ability of the eye to maintain its efficiency for a period of
work. As good results were not gotten, however, with the shade
for any of the systems as were given by the indirect system
without the shade. Since there was a still greater evenness of
surface brightness in the field of view in case of the indirect
system with the eye shade than without, the question arises why
19 This rim is about three inches in front of the observer's eye when the shade is in
position.
■ Hering standard white paper was used for this lining. The reflection coefficient
of the dark lining was about 6-8 per cent.
4/8 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
at least as good results were not obtained with the shade as
without. The answer, we believe, is to be found in terms of
the distraction to fixation and accommodation caused by the eye
shade even when a light lining was used. For the effect of a
shade on the eye even when the most favorable lining is em-
ployed is that of a constantly present distracting object with
its lower margin not far removed from the center of the field of
vision, and much nearer to the eye than are the objects which
the observer is called upon to discriminate. It will be noticed
also in Table XVII that the results were never so good for either
kind of shade for the direct and semi-indirect systems as for the
indirect. Since the evenness of surface brightness in the field
of view was not very different for the three systems in both
cases, this again probably indicates that the evenness of surface
brightness is not the only one of the distribution factors that has
to be taken into account in studying the effect of different con-
ditions of lighting on the eye.
These tests were made for the same installations that were used
in the distribution series. Since the use of the eye shade did not
affect the illumination of the room the reader is referred for the
illumination measurements to the tables of the distribution series.
The distribution of surface brightness in the field of vision, how-
ever, was strongly affected. New measurements were made,
therefore, of the brightness of the prominent surfaces in the field
of vision. The tests were taken at Position I, see Fig. i, p. 452a
The prominent surfaces in the observer's field of vision working
in this position were J, K, and L (see Fig. 4, p. 452b) ; the top
of the table carrying test and recording apparatus, immediately
in front of the observer and below the level of his eyes; the test
card ; the reading page in the 45 deg. position ; and the white and
dark lining of the eye shade as seen by the observer when the
shade was in position over his eyes. The measurements of the
brightness of the lining of the eye shades as seen by the observer
when the shades were in position were made as follows. A sur-
face in front of the observer was made to match in brightness the
lining of the shade as it was seen by him. The brightness of this
surface was then measured by the ' method described on page
452. In procuring the match between the comparison surface and
FERREE AND RAND: EFFICIENCY OF THE EVE 479
the lining of the shade the series of Hering matt gray papers was
employed. This series consists of 50 shades ranging from a white
with a reflection coefficient of 75 per cent, to black. Sheets of
these differing in brightness were placed in a vertical position at
a given distance in front of the observer until an approximate
match was made with the lining of the shade. The gradations
needed to get the final match were secured by moving the sur-
face to and from the observer and by tilting it at different angles
with the line of sight. The former adjustment carried it into
parts of the room having different intensities of illumination and
the latter turned it so as to receive a greater or less amount of
light. In making the brightness measurements, care was taken
to have the receiving surface of the photometer arm normal at
its central point to the line of sight taken by the observer when
the match was made. The results of these measurements are
shown in Table XIV. In Table XV are given some of the prom-
inent ratios of surface brightness in the field of vision for the
shade with the dark lining ; and in Table XVI, some of the prom-
inent ratios for the shade with the white lining. In Table XVII
are shown the results for the test for loss of efficiency for the
shade with the dark lining; and in Table XVIII for the shade
with the white lining. For purposes of comparison the results
of the three systems without a shade are repeated. These are
given in Table XIX. A graphic representation results of all
three tables is given in Chart IV.
TABLE XIV.— Eye Shade Series.
Showing the brightness measurements in candlepower per square inch
for the various surfaces in the field of vision for the direct, semi-indirect and
indirect systems used when the eyes were shielded in turn by an opaque
eye shade with a dark lining, and an opaque eye shade with a white lining.
Surface Direct Semi-indi- Indirect
measured system rect system system
J 0.0014 O.OOI 0.00095
K 0.0063 0.0046 0.00255
L 0.0042 0.0027 0.00246
Table 0.0029 0.00255 0-00233
Test card 0.00308 0.003 0.00299
Reading page 450 position 0.004 0.0039 0.00431
White lining of eye shade 0.00197 0.00204 0.00207
Dark lining of eye shade 0.000091 0.00011 0.000126
480 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
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FERREE AND RAND: EFFICIENCY OF THE EVE
481
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482 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
TABLE XIX.— Eye-Shade Series.
Showing the eye's loss in efficiency as the result of 3 hours of work
under the direct, semi-indirect, and indirect systems of lighting employed
(No eye shade.)
Maximal
distance at
Foot-candles which test
, ■ , object can
Lighting Hori- Verti- be seen
system Watts zontal cal 45° Time clear
Indirect 800 5.2 1.36 3.5 9 A.M. 84.5
12 M. 84.5
Semi-indirect. 760 5.8 1.45 4.0 9A.M. 80.5
12 m. 79.5
Direct 880 4.2 1.41 2.6 9 A.M. S1.0
12 M. 78.0
Total
time
clear
Work- -5- Ratios
ing Total Total total reduced
dis- time time time to common
tance clear blurred blurred standard
Indirect 67.5 135 45 3-°° 3-5
67.5 132 48 2.75 3.2
Semi-indirect 68.5 142 38 3.73 3.5
68.5 92 88 1.64 0.97
Direct 68.0 139 41 3.39 3.5
68.0 771 109 0.69 0.671
As yet we have not determined the effect of translucent shades
on the eye. In attempting to deal in a general way with this
class of shades we have the same type of difficulty to face that we
have in case of the semi-indirect reflector. That is, we may have
shades varying from transparent to opaque, and sharing in the
merits and demerits of each extreme. Our judgment would be,
however, that it would be very difficult to get a translucent shade
that would give as good results as an opaque shade with a light
lining; for the translucent shade when made sufficiently opaque
to give the needed reduction to the image of the source will
darken too much the upper half of the field of vision and thereby
simulate too much the condition given by the opaque shade with
the dark lining to give the best results for comfortable and effi-
cient seeing. Moreover, from the results that have already been
obtained with the opaque shade and from the principles it seems
fair to infer from these results, it seems very probable to us that
as good effects for seeing should not be expected from the use of
FERREE AND RAND: EFFICIENCY OF THE KVE
483
any kind of eye shade as may be gotten from lamp-shades. That
is. if we are to secure the best results for seeing, the shade should
be put on the lamp, not on the eye.
THE ANGLE AT WHICH THE LIGHT FALLS ON
THE WORK.
The object of these experiments was to find out whether the
CHART IV.— Eye Shade Series.
Showing the effect on loss of efficiency of opaque eye shades with dark and
with white lining for the installations direct, semi-indirect, and indirect
with the same intensity of light at the point of work. Chart A shows
results without shade ; Chart B, with shade having dark lining; Chart C"
with shade having white lining.
CHART A
— INC
M£I±_
\Nm*-,
•
s
5S
cr
SEMI -INDIRECT
difference in the angle at which the light falls on the work pro-
duces an effect on the eye that can be detected by the test we
have used for loss of efficiency. For the purpose of this pre-
liminary investigation it was decided to make the general illumi-
nation of the room such as to cause the eye little loss of effi-
6
484 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
ciency as the result of the period of work ; and to add to that
at the point of work a component of light which was less diffuse
in order that the amount of light entering the eye would be more
dependent upon the angle at which the reading page was held.
The general illumination was obtained from the indirect system
used in the work of the preceding sections with lamps totalling
800 watts. The less diffuse component at the point of work
was obtained from a 60-watt lamp with a porcelain reflector of
the desk lamp type. This lamp was turned into the horizontal
position and was placed behind the observer and to the left so
that the light came over the left shoulder. When in the position
for which the test was taken the tip of the lamp was slightly
above the level of the observer's eye, at a distance of 1 meter
from the left eye.
The illumination and brightness measurements for the test
room illuminated by the indirect system, 800 watts, are given on
pp. 469 and 471. These measurements were not greatly changed
by the addition of the 60-watt lamp behind the observer. Because
of the presence of this lamp, however, the following measurements
were added to those given on pp. 469 and 471 : the horizontal,
vertical, and 45 deg. components of light at the point of work ; the
brightness of the test card in place for the test ; and the brightness
of the reading page when held respectively in the positions which
gave the least and the greatest amounts of specular reflection.
The illumination measurements at the point of work are given in
Table XX. The brightness of the test card was 0.00365 cp. per
sq. in. ; of the reading page in the position that gave the least
amount of specular reflection, 0.0059 cp. per sq. in. ; and in the
position that gave the greatest amount of specular reflection,
0.0077 CP- Per S{1- m- A mirror surface was used as an aid in
locating the position of least and greatest specular reflection.
The results of the test for three hours of work done with the
reading page in these two positions are also given in Table XX.
A graphic representation of the results of this table is shown in
Chart V.
THE EFFECT OF DIFFERENT CONDITIONS OF LIGHTING
ON THE FIXATION MUSCLES OF THE EYE.
The test we have employed thus far in the conduct of our
FERREE AND RAND: EFFICIENCY OF THE EYE
485
work is one designed to show the effect of different conditions of
lighting on the ability of the eye to hold its efficiency for clear
seeing for a period of three minutes. In itself this test is not
TABLE XX.— The Angle at Which the Light Falls on the Work.
Showing the effect on loss of efficiency of the angle at which the light
falls on the work.
Kind of
reflection
from read-
ing page
during
work period
Foot-candles at
test-card
Hori-
zon-
tal
Diffuse 5.3
Specular 5.3
Work-
ing
dis-
tance
Diffuse 73
73
Specular 73
73
Verti-
cal
I.84
Total
time
clear
139
137
137
132
45°
3-9
3-9
Total
time
blurred
41
43
43
Time
9 A.M.
12 M.
9 AM.
12 M.
Total
time
clear
total
time
blurred
3-39
3.18
3.18
2.73
Maximal
distance
at which
test ob-
ject can
be seen
clear
89
89
89
Ratios
reduced
to com-
mon
standard
3-5
3-27
3-5
3-o
analytical in principle. The results, as is stated above, are ex-
pressed in terms of an aggregate loss of function. The con-
tributive factors may be inferred from the nature of the test, but
CHART V.— The Angle at Which the Light
Falls on the Work.
Showing the effect on loss of efficiency of the angle
at which the light falls on the work.
1 ~3~
the test is not in itself designed to separate them out. And
indeed it is a question whether any practical good can accrue to
the practise of lighting from a knowledge of just what part of
486 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
the visual apparatus it is that falls off in function as the result
of an unfavorable condition of lighting. Obviously the chief
need is to find out what are the conditions that cause the eye to
lose its ability to see clearly and to avoid these conditions in
planning and installing a lighting system. From the beginning
we have had in mind, however, an analysis of effect. Our tests
for the sensitivity of the retina showed, for example, that very
little, if any, of the difference in results we have gotten for the
four types of lighting we have employed can be ascribed to a
loss in the efficiency of the retina, or the light sensitive part of
the visual apparatus. Three sets of factors are involved in clear
seeing : ( 1 ) the sensitivity of the eye to colored and white light ;
(2) the ability to make fine space discriminations which is in
part dependent upon our third factor; and (3) accurate fixation
and accommodation. Both fixation and accommodation are the
result of muscular action. When the muscles lose in tone because
of excessive use or by sharing in a general condition or state of
the body, the eye loses correspondingly in its power to sustain
clear seeing. If, for example, the muscles of accommodation
have fallen off in efficiency the lens is no longer held in the
adjustment needed to bring the light to a sharp focus on the
retina and loss of detail and blurring result ; or, if it be the fixa-
tion muscles that have suffered the loss, the eyes cannot be con-
tinuously held in such a position that the images of the object
viewed fall symmetrically on the fovea of each. When this latter
condition is present loss of detail results from two causes. (1)
The fovea and region immediately surrounding it are the most
highly developed parts of the retina and the best fitted for the light
and space discriminations needed for clear seeing. Moreover, the
refracting media of the eye give the clearest images when the
axis of the cone of rays from the object viewed deviates as little
as possible, consistent with the mechanism of the eye, from the
optic axis. And (2) if the images in the two eyes do not fall
more or less symmetrically upon the fovea of each they are not
accurately combined into one, and blurring and loss of detail
results from the doubling of the objects seen. It is our purpose
as fast as possible to isolate the effect of the three systems of
lighting we have used on each of the above named factors. In
FERREE AND RAND: EFFICIENCY OF THE EYE 487
the work of the present section the effect of these systems on
the fixation muscles has been studied.
The doubling of the image seen when the fixation muscles lose
their power of co-ordinated action furnishes us with our clue
for a test for the loss of efficiency of these muscles. That is,
just as blurring and the loss of ability to discriminate detail is
taken as the criterion of the loss of acuity of vision, so will the
doubling of the image seen be taken as our index of the loss of
the co-ordinated action of the fixation muscles. If one were to
stare continuously for an interval of time with natural vision at
a simple test object, as, for example, a vertical line, doubling
might be detected especially if there had been protracted strain
or considerable loss of power to co-ordinate. For the purpose of
our work, however, greater sensitivity than this would be
needed. Obviously sensitivity can be added by putting the eyes
under strain to combine their images. When this is done, even
when the muscles are fresh, if the object is looked at or fixated
for an interval of time it will be seen alternately a.s one and as
two. The proportion or ratio of the time seen as one to the
time seen as two can be regulated by the amount of initial strain
under which the eyes are put to combine their images. The regu-
lation of this ratio is empirical and of importance; for as is the
case with the test for loss of efficiency for clear seeing, the sen-
sitivity of the test depends to a considerable extent upon the
initial value that is given to this ratio. The eyes may be put
under strain to combine their images by interposing between
them and the object viewed weak prisms and so adjusting them
and regulating the distance of the object from the eye that with the
maximum of effort to see it as one it is seen alternately as one and
as two in the proportion desired.21 This result can be accom-
21 It would seem that the above principle might be utilized to advantage by the
opthalmologist in testing the extrinsic muscles of the eye. The abduction and adduc-
tion tests, for example, determine only what the muscles are able to do by momen-
tary effort. Obviously, however, it is not what the muscles are able to do by a
momentary effort or jerk that measures their ability to hold the eyes continuously
adjusted for work. It is rather their endurance or what they are able to accomplish
in an interval of time. An expression may be had for this either for the eyes con-
jointly or separately by the method described above. That is, the prisms may be put
in front of either one or both eyes and the ratio be determined of the time the
object is seen as one or as two for whatever interval of time the operator may select.
Similarly, it seems to the writers that the time element might be introduced to ad-
( Continued on next page. )
488 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
plished still more conveniently, however, by using an adaptation
of the Brewster stereoscope. In this case a stereograph consisting
of two vertical lines exactly alike may be used as the test object.
In the stereograph employed in our test the vertical lines were
2.5 cm. long and were printed on the card 4.5 cm. apart or at
2.25 cm. from the center of the card. When this was put in a
sliding carrier and was made to approach the eyes, a position
was reached at which with the maximum of effort the observer
was no longer able to see the two vertical lines as one. They
were seen alternately as one and as two. In making the test the
hood was removed from the stereoscope so that the eyes were
fully exposed to the conditions of illumination that were being
tested. The stereoscope was mounted in front of the eyes of
the observer in position at the point of work. The distance of
the carrier containing the test object from the observer's eyes
was adjusted until the proper ratio of time seen as one and time
seen as two was obtained. Having determined this position a
record was made of the time seen as one and the time seen as
two for three minutes at the beginning and the close of work. The
ratio of the sum of these intervals may in either case be taken
as a measure at that time of the power of the fixation muscles
to act in co-ordination for three minutes of continuous effort;
and the decrease in this ratio from the beginning to the close of
work may be taken as a measure of the loss in that power, sus-
tained as the result of work. In making this test the same re-
cording apparatus was used as was employed in the test for loss
of efficiency for clear seeing. That is, the record was traced
on a kymograph by means of an electro-magnetic marker and a
vantage into the visual acuity test used by the ophthalmologist when the cycloplegic
is not employed or in cases of post-cycloplegic refraction. Is it, for example, enough
to know that the eye has 20/20 acuity or can discriminate a certain standard visual
angle by momentary effort? Would it not give a more complete repreentation of
the functional condition of the eye to know what it can discriminate clearly through
an interval of time; or better still perhaps, for what proportion of an interval of
time it can discriminate a certain detail or standard visual angle clearly? For ex-
ample, just as a fatigued eye may for the moment under the spur of the test over-
come the functional results of fatigue, so might small errors of refraction be overcome
for the moment by muscular effort, especially in the cases in which fhe muscles of
the eye are unusually strong. But just as the fatigued muscle can not do this through
an interval of time, so it would seem that a residual error of refraction might not
be so easily masked through an interval of time by means of muscular effort. In
short, this form of test is suggested as affording possibly a closer approximation to
the conditions and demands imposed upon the eye during a period of work than is
afforded by the acuity test based upon the momentary judgment.
FERREE AND RAND: EFFICIENCY OF THE EYE
489
telegraph key, and a time line was run beneath the record by
means of a Jacquet chronograph registering seconds.
The test for the effect on the fixation muscles of a period of
work was made under the same installations, conditions of
work, and with the same observers that were used in the dis-
tribution series. The test, however, was made at only one of the
positions used in that series, namely, the position at which the
greatest loss of efficiency was obtained. (See Position I, Fig. 1,
p. 452a.) At this point, it will be remembered, six of the lighting
TABLE XXI.— Fixation Muscles Series.
Showing the loss of efficiency of the fixation muscles as the result of 3
hours of work under the direct, semi-indirect, and indirect
systems of lighting employed.
Watts
Foot-candli
ss
Time
Distance
at which
test ob-
ject is
normally
seen single
Lighting S3'stem
Hori-
zon-
1 tal
Verti-
cal
45°
800
4.2
0.99
2-5
9 A.M.
12 M.
18
18
Semi-indirect
760
4.8
0.98
2.6
9 A.M.
12 M.
18
18
880
3-9
I.o
I.99
9 A.M.
12 M.
18
18
Work-
ing
dis-
tance
Total
time
single
Total
time
double
Total
time
single
total
time
double
Ratios
reduced to
common
standard
22
142
38
3-7
3-5
22
140
40
3-5
3-3i
22
141
39
3-6
3-5
22
138
42
3.28
3-24
20
153
151
27
29
5-66
5-21
3-5
3-21
20
units were in the field of view. The specification of the lighting
effects produced by these installations are given on pp. 452a-459
Nothing need be added at this point to these specifications but
the brightness of the stereograph or the test object in position
for the three systems of lighting, and the illumination meas-
urements at the test card. The brightness measurements are as
follows. The brightness of the card, corrected for the ab-
sorption of the prisms of the stereoscope was for the direct
system 0.00172 cp. per sq. in.; for the semi-indirect system,
490 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
0.00163 cp. per sq. in.; and for the indirect system, 0.00167 cp.
per sq. in. New illumination measurements were needed at the
test card because the card had to be moved closer to the eyes
than was the case in the tests for loss of efficiency for clear
seeing, which brought it into a region of different illumination.
These measurements are given in Table XXI. The results of
our tests for loss of efficiency of the fixation muscles for the
three systems of lighting are given also in this table. These re-
sults show (a) that very little loss of co-ordination is suffered by
the fixation muscles as the result of three hours of work under the
systems selected; and (b) that there is very little difference in
CHART VI.— Fixation Muscle Series.
Showing the loss of efficiency of the fixation muscles
as the result of 3 hours of work under the direct,
semi-indirect, and iudirect systems of lighting em-
ployed.
Foot-candles
Lighting system Watts
Indirect 800
Semi-indirect . • 760
Direct 880
Horizontal
4.2
4.8
3-9
Vertical
0.99
O.98
1.0
45°
2-5
2.6
I.99
INDIRECT i
SEMI- INDIRECT
"-DIRECT
the effect for the three systems. Since there is no reason for think-
ing that the test has not as great sensitivity as the test for loss of
efficiency for clear seeing, and since the same observers, condi-
tions of lighting and working were used as in the former tests, it
does not seem to us at this time that the loss of efficiency for clear
seeing that is sustained under these conditions, shown by the
former tests, can be ascribed to any great extent to an effect on
the muscles of fixation. In a later report experiments will be
described in which the effect on the muscles of accommodation
has been studied.
A graphic representation of the results of Table XXI is shown
in Chart VI.
I'KKREE AND RAND: EFFICIENCY OF THE EYE 491
THE EFFECT OF MOTION PICTURES ON THE EFFICIENCY
OF THE EYE.
The belief that motion pictures subject the eyes to undue
strain is too prevalent to need more than mention in passing.
All are familiar with the conditions, — the initially dark-adapted
and highly sensitized eye, the comparatively brilliant screen with
its dark surrounding field, the flickering light, and the shifting
and very often unsteady pictures. We have already seen that
differences in surface brightness of considerable magnitude in
the field of vision cause loss of efficiency and produce discom-
fort, and we have discussed the causes for these effects. We have
nothing further to add to that discussion here. We are, how-
ever, facing for the first time in our work the question of the
effect upon the eye of a flickering light and lack of steadiness in
the object viewed. The following reason is suggested why a
flickering or unsteady picture may cause loss of efficiency. The
eye is so constituted that when its images lose in clearness or
distinctness it is incited to a muscular readjustment to bring
about the clearness needed. Ordinarily in seeing, the conditions
for loss in clearness come about primarily through the difference
in the distance or direction from the eye of the objects which
are successively viewed. In motion pictures, however, the chang-
ing clearness of the objects viewed is not due to any change in
their distance or direction from the eye; nor to anything in fact
which the readjustment of the eye can remedy to any consider-
able degree. The effort expended, therefore, is of little avail for
seeing, if, indeed, the new setting of the parts is not a detriment
to clear seeing and a condition which in turn must be corrected.
This should, and doubtless does, lead to muscular strain and
loss of efficiency. It was decided, therefore, to make an explora-
tive investigation to determine whether there is an effect of motion
pictures on the eye which can be detected by our test for loss of
efficiency. The tests were conducted in a local theater, selected
primarily because of the favorable conditions that prevailed. The
definition at the screen was good and the pictures were unusually
steady and free from flicker. The conditions were, we think, fairly
representative of what is found in the better class of motion
picture houses.
492 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
The tests were taken immediately before and after two hours
of observation of the pictures. During the exhibition the ob-
server sat directly in front of the center of the screen. The
observation was made at successive times at three distances from
the screen, — in the front, middle, and the back of the house.
These positions were respectively 25, 48, and 71 ft. (7.62, 14.6,
and 21.6 m.) from the screen. The room in which the pictures
were shown was 78 ft. (23.7 m.) long and 48 ft. (14.6 m.) wide.
The tests were taken in a room 14 ft. (4.2 m.) long, 9 ft. (2.74
m.) wide, 11 ft. (3.35 m.) high, adjoining the stage. The walls
and ceiling of this room were of rough plaster, painted a flat white.
When taking the test the observer sat facing one of the side walls
of the room, 1.5 m. distant. The room was lighted for the pur-
pose of the test by one 100-watt and one 60-watt clear tungsten
lamp suspended behind and slightly to the right of the observer
when in position for the test, at about 2 ft. (0.6 m.) above the
level of his eyes. The source of light was thus entirely out of
the field of view and the light fell evenly and without shadow on
the test card and the wall in front of the observer. At the point
of the test card, the illumination measured with the receiving test
plate of the photometer in the horizontal plane was 1.3 foot-
candles; in the vertical plane, 1.9 foot-candles; and in the 45 deg.
plane, 2.3 foot-candles. The surface brightness of the test card
was 0.003256 cp. per sq. in., and that of the wall directly behind
the card was 0.002288 cp. per sq. in. The distribution of surface
brightness on the wall which the observer faced was very even.
At the point of maximum brightness to the right of the observer,
as nearly as that point could be located, the brilliancy was 0.00308
cp. per sq. in. ; and to the left of the observer, 0.002024 cp. per
sq. in.
In order that there might be no intermission between the pic-
tures for changing the films, two projection machines were used.
The following is the specification of the apparatus employed as
given by the operator.
Type of machine, Powers 6 — A Projector.
Lens equipment, 1 pair pearl white condensers, 6l/> in. F. L.
1 Bausch and Lomb objective combination.
4}i in. E. F.
FERREE AND RAND: EFFICIENCY OF THE EYE 493
Lamp, i io,ooo-cp. adjustable arc.
Carbons, y% in. cored bio's.
Current, 22 volt a. c. through Halberg transformer.
Line current, 28-30 amperes.
Arc voltage, 45-50 volts.
Length of throw or distance from objective to screen, J2 ft.
(21.9 m.)
Screen, sheet muslin sized and coated with flat white alabastine.
Speed of film through machine, 66 ft. 8 in. (20.3 m.) per min.
Number of pictures per 1 ft. (0.3 m.) of film, 16.
Size of picture on film, y^ in. (1.9 cm.) high by 15/16 in- (2.38
cm.) wide.
Size of picture on screen, 11 ft. (3.35 m.) high by 14 ft. (4.26
m.) wide.
Approximate brightness of screen with film removed from pro-
jector, 3.47 cp. per sq. in.
Exceptional steadiness, it may be said, is given to the move-
ment of the film and, therefore, to the picture in this type of pro-
jector by the special type of intermittent movement that is em-
ployed. Details of this movement need not be given here. As
has already been stated, our reason for making the test in this
particular theater was the comparative steadiness of the pictures
and the comparative freedom from flicker, that was obtained.
The results of the tests are shown in Table XXII. Quite a
great deal of loss of efficiency is shown as the result of two
hours of observation. The nearer the observer was to the screen,
the greater was this loss found to be. The loss, however, so far
as we can tell, is no greater than is caused by steady work under
the direct and semi-indirect installations of lighting used in our
distribution series. Unfortunately, we have not for the pur-
poses of comparison, results for the same observer for the same
length of time of exposure for the two sets of condition. The
loss for observer R for two hours observation of the motion
pictures was not nearly so great as for three hours of reading
from good print and paper, under the direct and semi-indirect
systems of lighting. But comparing the results for observer G for
two hours of reading from the same type and paper with those
for observer R for two hours observation of the pictures the
494 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
loss seems to be about the same. That is, our results indicate
that while the eyes are strained a great deal by the observation
TABLE XXII.— Motion Picture Series.
Showing the loss of efficiency of the eye caused by two hours' observation
of motion pictures.
Maximal
Total
distance
time
at which
clear
Ratios
test ob-
Work-
-i-
reduced
ject can
ing
Total
Total
total
to com-
be seen
dis-
time
time
time
mon
Position
Time
clear
tance
clear
blurred
blurred
standard
25 ft. (7.62 m.)
from projec-
tion screen . •
8 P.M.
86.2
70.5
123
57
2.14
3-5
IO P.M.
86.1
70.5
95
85
1. 12
1.79
48 ft. (14.63 m.)
from projec-
tion screen • .
8 P.M.
85.8
71.0
128
52
2.46
3-5
IO P.M.
85.6
71.0
108
72
1-5
2.13
71 ft. (21.64m.)
from projec-
tion screen. .
8 P.M.
86.0
69.0
137
43
3-19
3-5
IO P.M.
86.0
69.0
124
56
2.2
2.42
CHART VII. Motion Picture Series.
Showing the loss of efficiency of the eye caused by two
hours observation of motion pictures.
Position A 25 ft. from projection screen
Position B 48 ft. from projection screen
Position C 71 ft. from projection screen
POSITION C
B
of moving pictures, even in the better moving picture houses, they
are damaged little more by that in all probability than they are by
FERREE AND RAND: EFFICIENCY OF THE EYE
495
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496 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
reading steadily the same length of time under the greater part of
the lighting that is now in actual use.
A graphic representation of the results of Table XXII is given
in Chart VII. For the sake of comparing the effect of motion
pictures on the eyes with the effect of reading steadily under the
direct, semi-indirect, and indirect systems of lighting we have
employed, Chart VIII has been prepared.
THE TENDENCY OF DIFFERENT LIGHTING CONDITIONS TO
PRODUCE DISCOMFORT, AND A COMPARISON OF THE
TENDENCY OF THESE CONDITIONS TO CAUSE
LOSS OF EFFICIENCY AND TO PRODUCE
DISCOMFORT.
In the former papers we have held that the general level or
scale of efficiency of the fresh eye, loss of efficiency as the result
of work, and the tendency to produce discomfort are all separate
aspects of the problem of lighting in its relation to the eye, and
that our knowledge of each must be obtained by different methods
of investigation. A correlation between these three moments is
doubtless possible, but that correlation should be founded upon
the results of careful investigation ; it should not be assumed.
It is our purpose in this section of the paper to show the relative
tendency of the different conditions of lighting we have used to
produce discomfort, and to make a rough comparison of each con-
dition to cause loss of efficiency and to produce discomfort. Any
comparative study of the conditions producing discomfort neces-
sitates a means of estimating discomfort. It is obvious that the
core of the experience of discomfort is either a sensation or a com-
plex of sensations. As such it should have a limen or threshold
just as other sensations have ; and just as we are able in general to
estimate sensitivity in terms of the threshold value so should we in
this case be able to use the threshold value in estimating the eye's
sensitivity or liability to discomfort under a given lighting con-
dition. Threshold values are usually determined by finding how
much energy or intensity of a given stimulus, applied for a short
interval of time, is required to arouse a just noticeable sensation.
This form of procedure, however, is not adapted to the needs of
our problem. It is much better to reverse the process and find
how long the eye has to be exposed to a stimulus of a given in-
tensity to arouse just noticeable discomfort. Our threshold thus
FERREE AND RAND: EFFICIF.NCV OF THE EVE 497
becomes a time threshold and is measured in units of time instead
of units of intensity. In order to determine whether the judg-
ment of the threshold of discomfort can be made with certainty
and to perfect the method and to test in general its feasibility, an
abstract investigation was undertaken first, running through an
entire year, in which a better and more convenient control of
conditions could be secured than is possible in the investigation
of a concrete lighting situation. That is, we undertook to de-
termine the comparative sensitivity of the eye to discomfort when
a single source of light was exposed in different parts of the
field of vision. In order to carry out this investigation a lamp
house with a circular opening in one side 3 cm. in diameter was
attached to the arm of a perimeter in such a way that the opening
was always directed towards the observer's eye. In the lamp
house could be placed a lamp of whatever candlepower was de-
sired. The arm of the perimeter could be shifted to any meridian
in which it was desired to work and the lamp house could be
moved at will along this arm. It was thus possible to expose
the light for any length of time in any part of the field of vision
that was desired. Working in this way we have not only investi-
gated the effect of many types of variation of the position of the
light in the field of view, the effect of intensity of light, etc. ; but
we have studied and standardized the factors that influence the
sensitivity and reproducibility of the judgment and have given
our observers the training that was needed for the concrete in-
vestigation. In making the concrete investigation we have used
every variation of the conditions of lighting described in this
and the preceding paper. That is, the tendency to produce dis-
comfort, measured in terms of the value of the time threshold,
has been determined for all the conditions of lighting we have
used in the tests for loss of efficiency. Two cases may be made
of the investigation, — a determination of the tendency to cause
discomfort when the eye is at rest, and a determination of this
tendency when the eye is at work. Both of these cases were
included in our investigation. The following determinations were
made, (a) The time threshold of discomfort was gotten when
the observer was sitting with the accommodation muscles relaxed
and with the fixation muscles as nearly relaxed as was practica-
498 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
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FERREE AND rand: EFFICIENCY OF THE EYE
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500 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
ble under the conditions. That is, the observer sat in the positions
shown in Fig. i, p. 452a, and took an easy fixation of an area at the
level of the eye on the opposite wall of the room. The fixation dis-
tance, for example, for Position I, Fig. 1, p. 452a, was 22 ft. Since
blinking was found to be one of the variable factors which influ-
TABLE XXV.— Eye Shade Series.
Showing a comparison of the tendency of the direct, semi-indirect, and
indirect installations of lighting used in the distribution series to cause loss
of efficiency and to produce discomfort when the eye was protected by an
opaque eye shade with a dark lining and by an opaque eye shade with a
white lining. The loss of efficiency is the result of three hours of work.
The tendency to produce discomfort is estimated by the time required for
just noticeable discomfort to be set up.
Lining
of eye Lighting
shade system Watts
White Indirect 800
Semi-indirect . 760
Direct 880
Dark Indirect 800
Semi-indirect • 760
Direct 880
TABLE XXVI.— The Angle at which the Light Falls on the Work.
Showing a comparison of the tendency to cause loss of efficiency and to
produce discomfort of the angle at which the light falls on the work. The
loss of efficiency is the result of three hours of work. The tendency to pro-
duce discomfort is estimated by the time required for just noticeable dis-
comfort to be set up.
Time
limen of
discomfort
Per cent, loss in seconds
of efficiency (readiug)
6.6 95
14-3 SO
ence the tendency to produce discomfort, the amount of blinking
was made constant from test to test. This was accomplished by
having the observer blink at equal intervals during the test, timing
himself by means of the stroke of a metronome. The interval
most natural and suitable for this purpose was determined for
Time
limen
Time
of
limen
discom-
of
fort
discom-
Per-
in sec-
fort
Foot-candles
cent.
loss
of effi-
onds
(not
read-
in sec-
onds
(read-
Hori-
Verti-
zontal
cal
45°
ciency
ing)
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1.36
3-5
9-1
85
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1 41
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23
19
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19
15
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1. 41
2.6
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16
13
Foot-candles
reflection from
Hori-
Verti-
reading page
zontal
cal
45°
Diffuse
• 5-3
I.84
3-9
Specular- . .
• 5-3
I.84
3-9
FERREE AND RAND: EFFICIENCY OF THE EYE 501
each observer separately. In the results given in the follow-
ing table a three-second interval was used. And (b) the time
threshold of discomfort was determined when the observer was
reading from print and paper similar to that used in the loss
of efficiency tests. In these tests all the conditions were kept as
nearly the same as they were in the work on loss of efficiency as
was possible. The results of both of these sets of experiments
on the tendency to produce discomfort are shown in Tables
XXIII-XXVI. The tendency to produce discomfort should be
estimated, roughly speaking, probably as inversely proportional
to the time it was required for discomfort to be set up. The time
required for discomfort to be set up is given in the tables. In
order to make convenient a comparison of the tendency of the
various conditions of lighting to cause loss of efficiency and to
produce discomfort the percentage loss of efficiency caused by
the given lighting conditions is given in a parallel column in each
table. The percentage loss of efficiency was computed by divid-
ing the loss in the ratio of time seen clear to time seen blurred
sustained as a result of work by 3.5, the standard ratio to which
all the ratios at the beginning of work were reduced. A rough
correspondence of the tendency to produce discomfort and to
cause loss of efficiency will be noted in every case. This cor-
respondence by no means amounts to a 1 : 1 correlation, however.
In Table XXIII is given the comparison of the tendency to cause
loss of efficiency and to produce discomfort for the distribution
series; in Table XXIV, for the intensity series; in Table XXV,
for the eye shade series; and in Table XXVI, for the series
showing the effect of the angle at which the light falls on the
work.
In conclusion we wish to state that in this work, and the work
reported in the former papers, the purpose has been primarily
to procure methods of working and to find out, as broadly as
one may, the applicability of these methods to the problems sur-
rounding the hygiene of the eye. While in many places attention
has been called to results that seemed to have general significance,
the intention has been, in general, to limit all comments and
conclusions strictly to the conditions under which the work was
done.
502 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
SOME RECENT EXPERIMENTS ON VISION IN
ANIMALS.*
BY H. M. JOHNSON.
Synopsis: The Cebus capuchin monkey has visual acuity of the same
order as that of man. Under the same experimental conditions the
monkey yielded a stimulus-threshold of 57 seconds of visual angle as
compared with an average of 49 seconds with a mean variation of 3 per
cent, for five trained photometrists. Two chicks under the same condi-
tions gave stimulus-thresholds of over 4 minutes, while similar tests on
two dogs yielded negative results. The monkey's difference-threshold
for size of visible bands is as low as 3 per cent, under optimal conditions.
One chick failed to acquire discrimination on the basis of difference in
size ; another individual yielded threshold values some ten times greater
than those obtained for the monkey. The chick may be trained with
difficulty to distinguish large differences in direction between two systems
of striae whose members are respectively equal in width. The monkey,
after similar training on other problems, acquired this form of discrimi-
nation and perfected it during the first day's training. Determinations
were made by the discrimination method, the stimuli being two modified
Ives-Cobb visual acuity test objects. The results are consistent with those
obtained by other experimenters on color vision and discrimination on
the basis of difference in size and form. Detailed reports of the author's
experiments are to be found in the Journal of Animal Behavior.
Recent experimentation on vision in vertebrate animals has
bearing on certain factors considered in theories of evolution. The
Darwinian theory for example assumes that certain animals are
capable of making differential responses to specific differences in
visual objects. In the doctrine of sexual selection it is asserted
that certain pattern-markings of hair or plumage are of value to
the animal possessing them, in that they enable- their possessor to
secure a desirable mate. The doctrine of natural selection as-
serts that certain animals and birds are "protectively" colored or
marked, the patterns in question being hard to distinguish from
the animals' immediate environment. Conversely it is implied
that if the coloring or marking were different the animals' nat-
ural enemies could find him more readily. Certain experimen-
* A paper read at the eighth annual convention of the Illuminating Engineering
Society, Cleveland, O., September 21-24, 1914.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
JOHNSON: EXPERIMENTS ON VISION IN ANIMALS 503
ters on vision in animals are interested in the question whether
these theories attribute to certain animals better visual discrim-
inative ability than these animals can be experimentally shown
©
- a'
Wb.
(fooc/i
®
Home
Compartment.
Rfb.
Cfoodi
© ©
Fig.
to possess. This is one of several questions of general interest
which led to the present and other recent work.
The problems attacked require that the animal be placed in a
situation in which he can be made to establish a discrimination-
habit ; that in forming and in maintaining this habit other sources
504 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
of help than visual stimuli be excluded ; and that the visual stimuli
be controllable so that only the stimulus-characteristic under study
(e. g., difference of wave-length, intensity, extent, form, disposi-
tion of brightnesses, etc.) shall be effective. The most successful
method which has been utilized in this country is one which
Professors Robert M. Yerkes and John B. Watson developed.
The method is based on the fact that animals seek to obtain food
and to avoid punishment. The animal under study is required
to choose one feeding-place and to avoid another. The place to
be chosen is indicated solely by one visual object (the "positive
stimulus") and the place to be avoided is indicated by another
visual object (the "negative stimulus"). The two objects which
constitute the stimuli to be discriminated are interchangeable.
The details may be readily seen in the accompanying diagram.
Fig. 1. This represents in floor plan a box first used by Pro-
fessor Yerkes, as modified for the author's present work. The
animal is placed in a home-compartment H, from which he is
released through the exit-door at the end. Food is already present
in each of the food-compartments, Lfb and Rfb, which the animal
may enter by passing through Alley A1 or A2, as the case may be.
The test-objects, G1, G2, are presented to the animal at the win-
dows W1, W2, at the end of the respective alleys A1, A2. A false
floor is placed in each alley, hinged at the end next the window,
and supported at the free end by a light spring. These floors are
covered with brass strips which serve as electrodes, alternate
members being connected with corresponding poles of the second-
ary coil of an inductorium. A double-throw switch determines
which of these "punishment grills" shall receive the induced
charge. The charge is always placed on the grill under the
"negative" stimulus. When the animal steps into the alley he
depresses the punishment grill, and in so doing closes the circuit
through the primary coil and breaks the circuit through one of
the signal lamps. In this way the choice is recorded automatically,
and it is not necessary for the experimenter to watch the animal
while the latter is in the act of choosing. The entrance door to
the food-box to be chosen is not opened until the animal has
entered the alley beneath the positive test-object. After the
animal has obtained the food, and the experimenter has recorded
JOHNSON: EXPERIMENTS ON VISION IN ANIMALS 505
the choice and arranged the stimuli for the next trial, the animal
is readmitted to the home compartment through a door opening
directly into it from the food-box, the exit-door of the latter
having been closed meantime. It should be remarked that certain
experimenters do not feed the animals for correct choices, but
punish them for incorrect choices. In such procedure the animal's
incentive is to escape from the home-compartment and to avoid
punishment. Other experimenters do not punish the animals for
incorrect choices, but feed them for correct choices. In the
present work the experimenter used both incentives combined.
The stimuli are presented in a right-left order predetermined by
the use of a well shuffled pack of cards. In 20 presentations the
positive stimulus will appear ten times at W1 and ten times at
W2, and the negative stimulus vice versa.
The first step in work of this kind is a course of training in
which the difference between the stimuli is quite large. The ani-
mal often forms a "position-habit" early in the work — invariably
choosing a certain food-box or choosing them in a perfectly reg-
ular order, regardless of the stimuli. These "position-habits" are
often persistent. If the type of discrimination is not difficult, a
bird or higher mammal can usually be trained to discriminate
perfectly in three or four weeks of daily training. Ten to twenty
trials or presentations are usually given in one daily "series."
After the animal has learned to attend to the test-objects the
number of trials may be increased — depending on the ease with
which the animal becomes restless or fatigued and upon his
capacity for food. The adult chick can be given from 50 to 60
trials in a single daily series if the amount of food given after
each choice is small. After the animal has learned to discrimi-
nate, the difference between the stimuli is reduced by small steps
until discrimination breaks down. This point is arbitrarily called
the animal's threshold. Experience has demonstrated this
method to be practicable and reliable if the stimuli are carefully
controlled.
Some experimenters have used for stimuli spectral bands,
diffused on plaster surfaces placed at the windows of the experi-
ment-box. They have prepared their stimuli in such a way that
the latter are accurately measurable and highly controllable as to
506 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
wave-length, intensity and saturation. They have obtained defi-
nite results, both positive and negative, on various animals as to
the range of wave-lengths to which the latter are sensitive, as
well as the degree of sensitiveness to difference of wave-length.
Other experimenters have used test-objects designed to test
the animals' ability or inability to discriminate similar forms
(e.g., circles) of varying sizes, and equivalent areas of varying
form. Some of these experimenters have also attached the
question of brightness-sensitivity by the same general method.
Some of these results will be mentioned presently.
The work of the author, which will be described in some detail,
grew out of an interest in some earlier work by Casteel on the
painted turtle. Casteel used the general method which has just
been described, the stimuli being alternate "black and white" striae
on cardboard fastened to the entrance to the food-boxes. In the
first experiments the striae on the positive and those on the nega-
tive field were respectively equal in width but lay in different direc-
tions. The animal was trained to choose the vertical system and
to reject the horizontal system. As Casteel was seeking to dem-
onstrate only that the turtles were responding to the striation as
such, he did not attempt to control the distance of test-objects
from the animals' eyes at which choice had to be made. He
obtained perfect discrimination with some animals when each
member of the two systems of striae was only 2 mm. wide. He
then presented the animals to another problem in which the striae
in the two systems were respectively unequal in width, but lying
in the same direction. He obtained perfect discrimination when
the width-difference was very large, and highly accurate choices
when the individual striae in one system were 3 mm. wide, and
in the other system 2 mm. wide. He did not attempt to find the
limits of the animals' stimulus-sensitivity or difference-sensitivity.
The writer has been working on a group of animals whose
retinal developments varies widely : the dog and cat, the domestic
chick, the Cebus monkey and the crow. The problem attacked is
the difference in pattern-vision which exists among these animals
under given conditions of illumination, the patterns used being
alternate dark and bright bands equal in width. In some problems
the variable factor is the band-width in the positive and negative
JOHNSON: EXPERIMENTS ON VISION IN ANIMALS S°7
systems, respectively; in other problems the variable factor is the
direction in which the two systems respectively lie. The first
question to be settled is, how wide must the individual members
of a system of striae be, for the striate field to be discriminate
at a given distance from a plain field, equal to the former in form,
area and mean brightness? For investigating this question the
writer used as stimuli two Ives-Cobb visual acuity test-objects,
indicated as G1, G2, in Fig. i. A diffusing screen of opal glass
was placed close behind each test-object. The latter were inde-
pendently illuminated and equated in brightness at 12.2 candles
per square meter. The sources used were 60-watt tungsten lamps,
connected in multiple, operated at a specific consumption of 1.25
watts per candle, the source of current being a 25-ampere storage
cell, and the current kept constant by the use of a voltmeter and
a rheostat. The two fields thus prepared were both striate. The
individual members of the negative system were about 0.1 mm.
wide, and it was assumed that at the distance given they were
too small to be resolved by the eye. The individual striae on the
positive field were made 2.23 mm. wide at the beginning of the
training, but this value was found too small for the dogs. The
mounting of the test-gratings used by Cobb was modified so as
to permit instantaneous change from a given band-width to an-
other given width, the gratings being rotated over each other by
a lever mechanism between limits determined by the setting of
two stops controlled by a micrometer screw. Thus either test-
object could be made at will to present a sensibly uniform field
or a field of a given striation.
A set of movable stops was constructed to fit into the experi-
ment-box in front of the entrance to alleys A1, A2. A different
stop was used for each animal, so as to make it impossible for
any of them to bring the eye nearer than 60 cm. to the test-
object without stepping into the alley and registering a choice.
The results obtained on the first dog — a pure-bred male English
bull-terrier — were negative, but not clearly so. He learned in
18 days to choose the alley under the positive test-object and
maintained discrimination for several days during which the
width of striae on the positive field was being reduced. The
experimenter introduced a control test, however, which revealed
508 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
that the animal had been testing the two punishment grills for
electrical charge, and maintaining discrimination on that basis.
(Hitherto the circuit through the primary coil of the inductorium
had been kept closed throughout the daily series of trials.) The
dog's behavior — sniffing violently at the entrances of the two
alleys — suggested that in this part of the work he may have been
sniffing for ozone or for some gas similarly generated, about the
charged electrodes. As soon as this source of help was removed
the dog ceased to discriminate. Very doubtful evidence of dis-
crimination was obtained when the band-width on the positive
field was about 4 mm. — near the limit of the instrument — but
this behavior was not persistent. A second dog — a pure-bred
female beagle-hound — did not give evidence of discrimination in
900 trials.
The two chicks — Indian gamecocks — learned the problem
readily. Chick 1 required very careful handling as he was easily
disturbed by punishment. He ceased to discriminate when the
band-width on the positive field was reduced to 0.71 mm., sub-
tending a visual angle of 4' 4" at the distance given. Chick 2 — a
more satisfactory subject — ceased to discriminate when the band-
width on the positive field was reduced to 0.74 mm.— subtending
a visual angle of 4' 14" at the distance given.
Monkey 2 — an adolescent Cebus capuchin — discriminated until
the band-width on the positive field was reduced to 0.163 mm. —
subtending a visual angle of 57". For practical purposes these
values may be taken as thresholds. Monkey i, a cat and a crow
died during the early stages of experimentation.
For purposes of comparison the author tested by the method of
limits, the visual acuity of five members of the staff of the Nela
Research Laboratory, using the same stimuli under the same
visual conditions as obtained in the work on the animals. All the
observers are skilled photometrists, four being physicists and one
a physiologist. J, whose values are shown separately, is a high
school student.
The results were as follows :
JOHNSON: EXPERIMENTS ON VISION IN ANIMALS 509
Mean
Observer threshold M. V. per cent
F 4S" 3
Co 50" 3
L 54" 3
Ca 48" 2
W 46" 4
Average 4c/' 3
J 54" 4
Monkey 2 57" Obtained by discrimination method
Chick 1 244//r Obtained by discrimination method
Chick II 254" Obtained by discrimination method
It should be stated explicitly that results obtained by the
method of limits are not directly comparable with those obtained
on a different subject by the discrimination method. The atti-
tude of the observer is different in the two cases, and the prob-
lem is somewhat different. It is believed however that one is safe
in taking these results as showing that the visual acuity of the
monkey is of the same order as that of the human subject ; that
the visual acuity of the chick is only 20 per cent, to 25 per cent.
that of the monkey and man; while the visual acuity of dog 1
(taking somewhat indefinite records as those of discrimination)
is not over 4 per cent, that of the monkey and man. The author is
hesitant regarding the assumption in the case of the dog; for
neither of these animals gave clear evidence of possessing sen-
sitivity to visual detail.
The second question taken up is, how great a difference in
band-width in two systems of horizontal striae distinguishable by
the animal as such, is necessary to enable the animal to discrimi-
nate them? This problem was attacked by the same general
method as described above. The same test-objects were used as
in the work on the first problem. For the chicks the brightness
was the same as before — 12 candles per square meter. The work
on the monkey was done somewhat later, and at a lower bright-
ness— 6.67 candles per square meter. The animals used were the
ones which had succeeded in learning the first problem — chicks
1 and 2 and monkey 2. Chick 1 failed to learn this problem.
The following table shows the difference-threshold values ob-
tained for chick 2 and monkey 2. The values taken for the chick
are those at the first breakdown of discrimination. Those for
the monkey are the values at which the average accuracy is
5IO TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
greater than 70 per cent, and less than 80 per cent. The results
are therefore not closely comparable, but the uncertainty is no
greater than other uncertainties inherent in the method. It is
impossible to work the chick successfully when discrimination is
difficult and the bird is receiving frequent punishment. This is
not true in the case of the monkey, if conditions are carefully
controlled.
The results are shown in the following table :
Chick 2.
Width of striae on
Difference in
per cent, of
standard stimulus
Positive field
Negative
: field
♦2.23 mm.
1.28 mm.
42
1.30 "
♦0.91
33
♦2.60 "
i-73
"
33
*3.I2 "
1.80
42
1.56 "
♦1.04
11
33
1.04 "
♦0.74
< i
40
Monkey 2.
1.772 mm.
♦1.561 mm.
14
*i.56i "
1. 301
1 1
17
0.8S7 "
♦0.780
i i
14
*o.78o "
0.673
"
14
0.610 "
♦0.520
(<
17
♦0.52O "
0.479
"
8 (See remarks below)
0.413 "
♦0.390
"
6
♦0.390 "
o.37i
( t
5
0.321 "
♦0.312
11
2.9
♦0.312 "
0.304
"
2.6
0.232 "
♦0.223
11
4
♦0.223 "
0.210
t <
6
♦0.19 1 "
O.I73
"
9
0.750 "
♦0.780
(i
3-8
♦0.780 "
0.764
"
2-f- (Greater than 2 an
* Standard stimulus.
The results appear in the table in the chronological order
of the tests. The results for monkey 2 show a progressive
diminution from the first step (value of standard stimulus
1. 561 mm.) to the fourth (standard = 0.312 mm.). It ap-
peared necessary, therefore, to determine by a control test whether
this was not due largely to effect of training. This test
joiinson: experiments on vision in animals 511
was made at standard stimulus = 0.780 mm., and it showed that
an important practise effect was present. The daily record
sheets suggest that during the work at the third step (standard
= 0.520 mm.) the animal acquired a higher standard of "atten-
tion" or a new criterion, which he maintained fairly well there-
after. Taking the later value as approximating the true thres-
hold, according to this mode of reaction, for that region, the
monkey's values in the different regions are quite close to those
obtained in rough tests on two human observers. Their optimal
results were at stimulus-values near his, and the threshold-values
where the standard stimulus was smaller than 0.3 mm. tended to
increase as did the monkey's. These results are not to be taken
as final, however, as more detailed and more careful work may
change them considerably.
A third problem is that of the least difference in direction
occupied by two systems of striae whose members are respec-
tively equal in width, which is necessary to effect discrimination.
This problem also was attacked by the same method and with
the same apparatus as the two preceding problems. The animals
used were chicks 1 and 2 and monkey 2. Chick 1 failed to learn
the problem, although he acquired perfect discrimination when a
large difference in band-width was presented together with a
difference in direction of 90°. Discrimination failed when the
difference in band-width was reduced. Chick 2 learned the
problem in 400 trials — with much greater difficulty than in the
problem of striate-plain discrimination. Monkey 2 learned the
problem during the first daily series, giving 90 per cent, accuracy
for the twenty trials, and 100 per cent, accuracy in the series
given the following day. His threshold and that of chick 2 have
not been finally determined at this writing. Dog 1 has also been
introduced to the problem, in order to ascertain if this problem
is easier for him than the first one, in which he probably failed.
To sum up: the monkey possesses sensitivity to visual detail
rivaling that of the best human subjects. His visual acuity is
four to five times as good as that shown by the chicks, and his
difference-sensitivity for size is proportionately much greater.
The factor of direction of striation is much more effective for
him than for the chicks.
512 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
A complete and satisfactory explanation of these results is not
possible at present. The tests were made in dark surroundings
but not with good darkness-adaptation. It is possible that the
visual conditions were more favorable for the monkey than for
the chicks and dogs: or the converse may be true. Since the
original presentation of this report my colleague, Dr. P. W. Cobb,
has tested the eyes of the animals used for refractive errors.
His report will be published shortly. It is sufficient to say here
that dog i and chick 2 were found practically free from refrac-
tive error, hence the disparity between their results and those
of monkey 2 is not explanable on that basis. The different
degrees of retinal development seem by far the most important
factor at present. The dog has no fovea and the existence of a
"sensitive area" in the paracentral region is doubtful. According
to Slonaker the chick is the only bird with the exception of the
guinea fowl which has not a well defined fovea. The monkey
has a retina almost like that of man. The crow possesses a well
developed fovea, nasal to the nerve-entrance. Many birds, espe-
cially birds of prey, have two foveas, one nasal the other temporal
to the entrance of the optic nerve. The nasal fovea is used in
monocular vision, the temporal fovea in binocular vision. If the
crow had yielded results closely comparable with those obtained
on the monkey, and the cat yielded results like those obtained on
the dogs, the author should have been tempted to refer the dif-
ferences in results to the differences in retinal structure. Such
interpretation might have to be modified after future tests on
optimal conditions of discrimination for the various animals.
It may be interesting to recall some results which other experi-
menters have obtained in work on other problems of vision with
the same species.
The dog has been tested for color-vision by numerous experi-
menters, but by none so far whose stimuli were adequately con-
trolled. There is no evidence whatever that he is sensitive to
differences of wave-length. There is good evidence that rodents,
whose retinal development is very like that of the dog, are color-
blind and have a shortened spectrum. "Watson has investigated
the range of effective wave-lengths for the chick, and reports
that it extends from A = 400 up to A = 715 pp, the maximum
JOHNSON: EXPERIMENTS ON VISION IN ANIMALS 513
lying near A = 500 fi/x, and the luminosity-curve being roughly
similar to that for the experimenter's eye under the same condi-
tions. Lashley and Watson have demonstrated the Purkinje
phenomenon in the chick, and have also obtained discrimination
between monochromatic bands, apparently based on wave-length
difference alone.
There is incomplete evidence that the Rhesus monkey dis-
criminates between monochromatic bands on the basis of wave-
length and that the wave-lengths in the region of red have a low
stimulating value. No reliable work on color-vision in the cat
and the crow has been published.
The dog has shown no evidence of ability to discriminate
between visual objects differing only in form. The writer once
worked on a single dog, using a circle and its equivalent square
as stimuli. Discrimination was established in about 1,000 trials
when the brightness of the positive stimulus was 4 times that of
the negative stimulus. Discrimination failed when the stimuli
were equated in brightness, and it was not re-established in 600
trials. Breed and Bingham have shown certain individual chicks
to be sensitive to differences of about 40 per cent, in luminous
intensity and area. They also trained several chicks to discrimi-
nate between visual objects differing only in form — circles from
equivalent triangles and squares. Watson also obtained positive
results with the Rhesus monkey, but has not yet published them.
Coburn, in some rather rough preliminary tests, obtained results
on the crow which compare very favorably with those obtained
by Breed and Bingham on the chick.
Nela Research Laboratory,
National Lamp Works of General Electric Co.,
Nela Park, Cleveland Ohio.
BIBLIOGRAPHY.
Yerkes, R. M. and Morguus, S.
The method of Pavloff in comparative psychology.
Psychological Bull., 1909, pp. 257, ff.
Yerkes, R. M. and Watson, John B.
Methods of studying vision in animals.
No. 2 Behavior Monographs, Cambridge, Mass., Henry Holt,
1911.
514 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
Yerkes, R. M.
The dancing mouse.
New York McMillans, 1907.
Lashley, K. S.
Visual discrimination of size and form in the albino rat.
Jour, of Animal Behavior, 1912, pp. 310, ff.
Breed, F. S.
Development of certain instincts and habits in chicks.
No. 1 Behavior Monographs.
Reactions of chicks to optical stimuli.
Jour, of Animal Behavior, 1912, pp. 280, ff.
Bingham, H. C.
Size and form preception in gallus domesticus.
Jour, of Animal Behavior, 1913, pp. 65 ff.
Coburn, Chas. B.
The behavior of the crow.
Jour, of Animal Behavior, 1914, pp. 185, ff.
Watson, John B.
Some experiments bearing upon color vision in monkeys.
Jour, of Comparative Neurology and Psychology, 1909, pp. I, ff.
Casteel, D. B.
Discriminative ability of the painted turtle.
Jour, of Animal Behavior, 191 1, pp. 1, ff.
Watson, John B.
Experiments upon the chick's spectrum.
Psychological Bulletin, 1913, pp. 71, f.
Watson, John B., and Watson, M. I.
A study of the responses of rodents to monochromatic light.
Jour, of Animal Behavior, 1913, pp. 1, ff.
Watson, John B.
Behavior — an introduction to comparative psychology.
N. Y., Henry Holt, 1914.
Johnson, H. M.
Visual pattern discrimination in the vertebrates.
Jour, of Animal Behavior, vol. 4, No. 5, 1914.
SeonakER, J. R.
A comparative study of the area of acute vision in vertebrates.
Jour, of Morphology, vol. 13, No. 3, 1897.
Vincent, Stella B.
The mammalian eye.
Jour, of Animal Behavior, vol. 2, 1912.
TRANSACTIONS
OF THE
Illuminating Engineering Society
Vol. X OCTOBER lO. 1915 NO. 7
REPORT OF THE COMMITTEE ON PROGRESS.*
Where is the way where light dwelleth? and as for
darkness, where is the place thereof? Job 38 : 19.
To the Illuminating Engineering Society :
During the past year there have occurred two events of strik-
ing significance, which may be symbolized by two flaming torches,
one signalizing destruction and conflagration, the other spreading
its glow over construction, progress and enlightenment. One
heralds animosity and antagonism; the other discloses amity and
friendly relationship. The one is the sign of war; the other a
proof of peace. In spite of the one progress has continued; in
conjunction with the other the art of illumination has been
extended. The European war, repellent in its awful carnage, has
afforded grim and hitherto undreamt of possibilities in the use
of light. The Panama-Pacific Exposition welcomes the whole
world and stands as a magnificent example of the art of applied
illumination.
Illuminating engineering is becoming recognized as a profes-
sion as attested by the employment of an illuminating engineer
to take care of the lighting of the Exposition and by the announce-
ment by the United States Government of examinations for the
position of illuminating engineer in the office of the supervising
architect at Washington.
The enormous demand for all sorts of material required by
the nations at war has necessitated night work in a large number
of foreign factories. This has stimulated interest abroad in
satisfactory and efficient systems of interior illumination.
It will be noted that the list of subjects covered by this year's
* A report presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
516 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
report is slightly different from that shown in the report of last
year. Some subjects are missing, others have been added. This
is natural, since progress is continually appearing in new
directions.
The committee again desire to express their thanks for the
help accorded by the engineers in charge of lighting in various
cities and to the representatives of those manufacturers who have
furnished information and data.
Respectfully submitted,
F. E. Cady, Chairman,
P. W. Cobb,
T. J. Litle, Jr.,
L. B. Marks,
T. W. Rolph.
SUBJECTS.
PAGE
Gas and Oil Lamps and Appurtenances 517
Electric Incandescent Lamps 520
Arc Lamps 525
Lamps for Projection Purposes 527
War 530
The Panama-Pacific Exposition 534
Street Lighting 537
Other Exterior Illumination 543
Interior Illumination 545
Globes, Reflectors and Fixtures 548
Photometry 550
Photography 556
Legislation 557
Illuminating Engineering in General 559
Literature 561
REPORT OF THE COMMITTEE ON PROGRESS 517
GAS AND OIL LAMPS AND APPURTENANCES.
Burners. — A very important development in incandescent gas
lighting is the recent introduction of an upright unit fitted with
three miniature mantles in soft form and made from artificial
cellulose fiber. This type of lamp operates well over a reasonably
fair range of gas pressure and qualities, is efficient and requires
no enclosing draught-inducing cylinders. It can replace open-
flame burners without glassware change on present fixtures and
furnishes a means of obtaining semi-indirect or indirect illumina-
tion.
Several new types of inverted burners provided with inclined
chute-like heat baffles to divert the products of combustion
entirely away from the fixtures have been worked out in sizes
giving approximately 100, 150 and 250 horizontal candlepower.
These units are furnished with non-tarnishable, heat-resisting
lacquer and are so constructed that the heat discharge vents are
completely hidden. Being entirely of metal they can be finished
to match the fixture on which they are to be used. The gas
lamp designed to take advantage of the fact that the hottest part
of the flame from a meeker or inverted Bunsen burner is in the
neighborhood of the small green inner cones and as mentioned in
last year's report has been in use in Germany1 and proved the
prediction of unusual sturdiness and long life.
An elaborate study of the room ventilating action of various
types of gas burners has been made in England.2 The results
show that the ventilating efficiency is greatest for upright burners ;
that of the inverted burners, those giving a clear passage for
the gases had the greatest ventilating efficiency ; that the addition
of deflectors intended to protect the fittings from the action of
the gases reduced the ventilating efficiency by as much as 9 per
cent. Experiments made in this country, however, show that
when the stack is properly designed, higher efficiencies are
obtained with deflectors due to a superheating of the mixture
before burning. Globes with a very open base had no effect on
the ventilating efficiency, but those with a constricted opening
produced a reduction dependent on the area of that opening.
ljuur.f. Gas., July 25, 1914, p. 741.
2 Jour, of Gas Light., June 8, 1915, p. 573.
518 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
To produce the best results with the use of gas for lighting
purposes, the character of the Bunsen flame used in conjunction
with gas mantles must not change materially. In order to enable
a manufacturer to ascertain how closely his service is maintain-
ing constancy of burner conditions, a gauge has been developed.3
It consists of a small, slender upright Bunsen tube of exact
design and carefully drilled orifice, mounted on the same base
with a pressure gauge. A scale is placed at the side of the Bunsen
tube in order to check the length of the inner cone. Any varia-
tion of the cone length above or below a specified point can be
easily noted. The gauge is not calibrated to indicate any specific
quality of gas, but will show only those changes which will
effect Bunsen burner service.
Despite the long life and high efficiency of the present day
gas mantle efforts are still being made4 by inventors to either
strengthen the structure or intensify the illuminating power by
the application of some solution after the mantle has been pur-
chased. Such efforts have not in the past been very successful.
Whether illuminating gas causes the fading of colors in fabrics
has been made the subject of careful testing,5 experiments having
been continued for a period of ninety days. It was found that
the deterioration of color either due to temperature, illumination,
or the products of combustion arising from the use of gas light-
ing is of no practical importance compared with the effect of
daylight.
Automatic Lighters. — The protected pilot tip so successfully
applied to outdoor gas arc lamps has now been modified for use
on indoor burners reducing the pilot flame outages to a minimum.
A very simple electric gas cock for the distance control of gas
burners has been produced. In Florence, Italy, a system of dis-
tance control for gas lighting6 has been in satisfactory use for
the past three years. As a result of a recent successful test by
military authorities, in which the city gas was shut off at a speci-
fied time and relighted after a predetermined period, it is expected
that this system will shortly be employed in Italian frontier and
3 Light. Jour. (U.S.), Dec, 1914, P- 82.
* Jour, of Gas Light., Feb. 23, 1915, p. 442.
5 III. Eng. (Lond.), June, 1915, p. 292.
8 Jour, of Gas Light., Mar, 2, 1915, p. 504.
REPORT OF THE COMMITTEE ON PROGRESS 51O,
coast towns. In general7 inventors are looking toward means for
making distance lighting by pressure waves selective.
Artificial daylight units using gas as the illuminant8 have been
developed and also units especially designed for photographic
work which will be mentioned later.
Heating Value. — The use of the calorific standard for gas in
place of the candlepower standard is increasing in this country.9
In many localities both standards are still required, but it seems
to be a quite general experience that if the gas is maintained at
the right calorific value, the candlepower value will be satisfac-
tory. At the 1914 convention of the American Gas Institute
there was referred to the Board of Directors the question of
adopting the Metropolitan No. 2 (Carpenter Argand) burner as
the standard burner in the determination of gas candlepower. It
has been suggested10 by the Bureau of Standards that "for those
places where a candlepower specification is necessary in order to
afford protection to users of open-flame lights, ... an open-
flame burner should be used in testing the gas candlepower." As
the number of open-flame burners used in this country is rela-
tively small the advisability of adopting this suggestion has been
seriously questioned. The Bureau also suggests that the adoption
of any standard burner might delay the present tendency toward
the adoption of heating value standards.
Data have been given11 of experiments which indicate that
calorific value, specific gravity, and gas candlepower do not defi-
nitely specify a gas for commercial purposes. Gases which are
identical in these properties may yet differ so in composition that
the resultant flame temperatures will differ greatly and hence
the performance of incandescent lighting appliances cannot be
predetermined on this basis. It has been found, however, that
heating values above 600 B. t. u. are not desirable for incandes-
cent gas lighting.
A method has been devised12 to enable a gas company to deter-
mine the candlepower of coal gas produced at night as well as
''Jour, of Gas Light., May 18, 1915, p. 409.
8 Light. Jour. (U.S.), Dec., 1915, p. 281. Proc. Amer. Gas Inst., vol. IX,
p. 886, 1914.
• Proc. Amer. Gas Inst., vol. IX, 1914, p. 367.
10 Gas Inst. News, March, 1915, p. 51.
11 Amer. Gas Light Jour., July 5, 1915, p. 1.
12 Amer. Gas. Lt. Jour., Apr. 5, 1915, p. 219.
520 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
by day. A holder, 3 ft. (0.90 m.) in diameter and 3 ft. high is
used and the flow of gas into it is regulated so that it will just
fill up during the night or during the day. Tests made on the
candlepower of the gas collected in the holder agreed exactly
with those made according to the "periodic method" in which
readings are taken periodically when the candlepower is at a
maximum, at a minimum, and at the average.
Oil Lamps. — Of late years13 the use of high pressure oil lamps
with incandescent mantles has considerably extended the employ-
ment of this illuminant. A Swedish type using Russian paraffine
oil, consists of two essential parts, the lamp itself and the con-
tainer for the oil. The latter is separated into two compartments,
one containing the air compressed to 6 atmospheres by means of
a small hand pump, the other holding about 2 gallons of oil. The
pressure used in the container is maintained constant at 2^2
atmospheres by means of a reducing valve. The lamp is started
by means of a little methylated spirit. A kerosene oil mantle
lamp is now being used in this country which on recent tests
showed a candlepower roughly twice, with a consumption of only
half as much oil as any one of several circular-wick center draft
luminous flame lamps of the ordinary type.
ELECTRIC INCANDESCENT LAMPS.
Gas-filled Tungsten Lamps. — While the development of the
tungsten filament electric incandescent lamp has been fairly rapid
as compared with that of the carbon filament type, it would seem
as if the progress each year was greater than that of the previous
year and that salesmen would hardly have time to dispose of one
product before an improved successor was available.
In last year's report14 reference was made to the sizes of non-
vacuum gas-filled tungsten lamps then available, 400 being the
lowest wattage for multiple burning. Now 100, 200 and 300-
watt sizes are made.15 In May all sizes from 200 to 1,000 watts
for circuits of 220 to 250 volts were 16 put on the market. In
England17 60-watt lamps of this type were announced July 1.
In the 60-watt and 100-watt lamps argon gas is used instead of
13 III. Eng. (Lond), Jan., 1915, p. 37.
14 Trans. I. E. S., 9, 1914. P- 522.
15 Report of Lamp Committee Nat. Elec. Light Assn., June, 1915.
16 Elec. Jour., June, 1915, p. 252.
17 Elec. Times, July 1, 1915, p. 1.
REPORT OF THE COMMITTEE ON PROGRESS 521
nitrogen. In Germany18 for 100 to 130-volt circuits, 40 and 60-
watt sizes, and for 200 to 250-volt circuits, 75 and 100-watt sizes
were advertised at about the same time.
It should be recalled, however, that, while in lamps with fila-
ments of large cross section, and, for multiple burning in general
of high wattage, the advantage gained in being able to run the
filaments at high temperatures and hence high lumens per watt
is great compared with the loss in wattage due to convection and
conduction in the gas, this advantage is greatly decreased, in the
case of filaments of small cross-section such as those used for
low wattages on multiple circuits, and hence the comparatively
slow introduction of the latter.
There has been a marked improvement in the various mechan-
ical features of the gas-filled tungsten lamp. Early lamps gave
trouble due to the loosening of the bases because of the effect
of the heat on the base cement. This has been remedied. A new
solder has been devised to overcome the former melting of the
solder at the junction of the leading-in wires and the base. Rust-
ing or scaling of the leading-in wires has been eliminated by the
use of a special coating. The distance between the filament and
the stem seal has been increased, thus decreasing the temperature
of the seal.
Another important step in advance lies in the standardizing of
the bulb,19 which now incorporates the good features of the round
and straight-side types, previously used, together with the long
neck containing a mica disk to keep the seal and base portion of
the lamp cool. The distance from the light center to the base has
been made the same for the 300 to 500-watt sizes so that one
type of fixture will do for any of these sizes. The use of the
gas-filled lamp in special colored bulbs for use in photography
will be mentioned under another caption.
Before the advent of the gas-filled tungsten lamp the use in
Germany of street lamps of the series type was limited. But20
the great advantage of the series gas-filled unit was evident, and
18 Elek. Zeit., June 24, 1915, p. 319.
18 N. E. L. A. Bui., Apr., 1915, p 246.
20 Zeit. f. Bel., Jan., 1915, p. 4.
522 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
hence an effort has been made to overcome the features formerly-
considered objectionable. A carborundum device has been used
to some extent as a shunting arrangement for burned-out lamps.
Physics. — There has been a continuation of the study of the
physical properties of the gas-filled tungsten lamp. Thus it has
been found that21 the spectral energy curves of a vacuum lamp
at 1.2 watts per candle and a spiralled-filament gas-filled lamp
operated at a color match with it, superpose very closely through-
out the infra-red spectrum. Tests have been made to determine
the effect of winding the filament in the gas-filled lamp in the
form of a spiral and the results indicated no marked difference
in the quality of the light emanating from the straight and
spiralled filaments of tungsten in an atmosphere of nitrogen.
When the luminous efficiency (ratio of the "visible" to the total
amount of radiation emitted) of these two types (straight and
spiral-wound filaments in a nitrogen atmosphere) was practically
the same, the candles-per-watt output was found to be 15 to 20
per cent, higher in the spiralled filament, owing to the lessening
of convection losses. When the straight filament was operating
at about 0.5 watt per candle and the spiralled filament was
operated so that the outside surface of a turn was set to the
same emissivity as that of the straight filament, the spectral
energy curves of the two showed that the spiralled filament
emitted about 7 per cent, more infra-red energy than the straight
filament. Hence the luminous efficiency of the latter under the
given conditions was 7 per cent, higher than the former.
Experiments have also been made22 showing that the so-called
"stationary" film of gas about the filament of a gas-filled lamp
as a matter of fact does not cling to the filament, but moves
upward along it.
Vacuum Tungsten Lamps. — Since last year's report there has
been an increase in the efficiency of the vacuum tungsten lamp
of from 7 to 10 per cent, in sizes below 150 watts. In July a
sign lamp for multiple circuits, 105 to 125 volts, was announced
21 Elec. World, Nov. 28, 1914, p. 1048.
22 Elec. World, Dec. 5, 1914, p. 1111.
REPORT OF THE COMMITTEE ON PROGRESS 523
using 7.5 watts and giving 5 candlepower. This is the smallest
wattage, standard lighting-circuit lamp yet manufactured. The
practise of introducing chemicals to delay the discoloration of
the bulb has been extended to include the 10, 15, and 20-watt sizes
and has permitted the operation of all vacuum lamps at higher
efficiencies. The spiral winding in a concentrated form is now
used in the 25, 40, and 60-watt sizes,23 in addition to those sizes
in which it was previously used. These lamps use the same size
bulbs and have the same average mean spherical efficiencies as
the regular type of the same wattage, but have a somewhat shorter
life. In Germany small lamps for signal purposes have been
developed24 which are designed to be burned in series with
apparatus or circuits whose active or inactive operation it is
desired to verify. These lamps are obtainable for a range of
current consumption from 0.4 to 12 amperes.
A method has been recently patented, in which25 the wires
sealed into the glass stem of electric lamps are coated with a
chemical salt, thereby making a better seal. The patent also
covers the use of metal plated wire for use in such seals.
In line with the continued efforts towards standardization there
has been considered a plan26 for settling upon two or three stand-
ard lamp voltages to be adopted as a basis for the manufacturer's
output. This will simplify specifications.
The completeness with which the gas-filled street series lamps
have superseded the vacuum type has resulted in the withdrawal
of the street series vacuum lamps from the listed lamp schedules.
The tantalum lamp has now disappeared from the market and
is being27 rapidly followed by the carbon lamp. The demand for
gem lamps has fallen off to such an extent that it is difficult to
retain the present limits of candlepower and wattage. In the
case of miniature lamps, the tungsten filament has so completely
23 Light. Jour., Mar., 1915, p. 65.
24 Elek. Zeit., Jan. 21, 1915, p. 27.
25 Elec. World, Apr. 24, 1915, p. 1043.
24 N. E. L. A. Bui., Mar., 1915, p. 169.
27 Eamp Com. Report, hoc. Cit.
524 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
replaced carbon that sales of tungsten comprise over 85 per cent.
of the total of miniature lamps sold.
Rating. — It has become the almost universal custom to rate
metal filament lamps in this country according to their watts input
and apparently this method of rating has served to raise the pre-
vailing standard of illumination. In England, however, a dis-
cussion before the British Illuminating Engineering Society28 re-
vealed the fact that this method of rating is by no means generally
accepted as satisfactory. The preponderance of opinion seemed
to be in favor of a return to some form of candlepower rating
with a difference of opinion as to whether the unit should be the
mean spherical candle or the lumen. In Germany also the sub-
ject has been considered at29 a series of conferences held by the
German Lamp Manufacturers who proposed the continuance of
the voltage-wattage rating. The lighting committee of the Ger-
man Association of Electrical Engineers discussed this proposal,
but could come to no full agreement on the subject. A30 repre-
sentative from the Associations of Central Stations urged that
it should be required by law to state the voltage, the upper and
lower hemispherical candlepower, the total watts consumed and
the watts-per-candle.
At the request of the31 Society of Motor Manufacturers and
Traders the British Engineering Standards Committee has been
investigating standard tungsten filament lamps of the vacuum
type for automobiles. The question of whether such lamps
should be rated at all in candlepower is receiving the attention
of the committee and in the meantime they are rated in actual
watts or nominal candlepower. Standard bulbs and standard volt-
ages are defined. For headlights a standard distance of 30 mm.
from the contact plates to the center of the filament is prescribed.
In Germany the gas-filled lamps were formerly widely adver-
tised as "half -watt" lamps. Recently32 the largest manufacturers
have made a determined effort to get away from this term, real-
izing that it is as misleading, and hence a cause of trouble, as the
old designation of "2,000 candlepower" was in the case of arc
lamps.
2S III. Eng. (Lond.), Apr., 1915, p. 167.
29 Elek. Zeit., May 13, 1915, p. 236.
30 Elek. Zeit., May 20, 1915, p. 248.
81 Elec. Eng. (Lond.), Feb. 18,1915, p. 69.
32 Zeit. f. Bel., Jan., 1915, p. IX.
REPORT OF THE COMMITTEE ON PROGRESS 525
Physics. — The disappearance of almost any kind of a gas
introduced at low pressure into a bulb containing an incandescent
tungsten filament has been investigated and it33 has been found
that there are four classes of reaction involved. The filament is
directly affected by the gas; or the gas reacts with the vapor
given off by the filament; or the filament acts catalytically on
the gas, producing a chemical change in the gas, but no perma-
nent change in the filament ; or the gas is chemically changed or
made to react with the filament by means of electric discharges
through the gas.
Studies have been made also on the34 temperature distribution
in the neighborhood of a cooling junction of an electric incan-
descent lamp filament, and of the thermal conductivities of tung-
sten, tantalum, and carbon at incandescent temperatures.
ARC LAMPS.
A flaming arc lamp has been developed35 in which the positive
electrode is covered by an outside cylindrical layer of illuminating
salts, which protect the inner electrode core against the oxygen
of the air so that consumption is reduced. The electrode is of
homogeneous carbon and the layer used is a mixture of calcium
fluoride, sodium tungstate and potassium chromate. The nega-
tive electrode is an ordinary homogeneous carbon with a central
core. The electrodes must be used vertically and are said to
have a life of from 40 to 50 hours. The specific consumption
including the series resistance for direct current is given as 0.14
watt per candle.
In the report of the Committee on Progress for 1913, reference
was made36 to some work on the relation of pressure and tem-
perature in arc lamps. This work has been continued37 and some
striking results have been obtained. From these results the true
temperature of the evaporating solid crater of the positive carbon
at atmospheric pressure was deduced as 4,200° centigrade abso-
lute, a value higher by 2000 or 3000 than that generally ac-
cepted heretofore. The temperature of the negative crater was
found to be lower by several hundred degrees. If the pressure
33 Elec. World, May 15, 1915, p. 1245.
34 Phys. Rev., vol. 4, 1914, pp. 524 and 535-
33 Elek. Zeit., Nov. 26, 1914, p. 1079.
M Trans. I. E. S., Oct, 1913. P- 328.
31 Zeit. f. Beleu., Jan., 1915-
526 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
is decreased below one atmosphere the temperature of the posi-
tive crater decreases. When the atmospheric pressure is in-
creased the temperature of the positive crater increases with a
corresponding greatly increased efficiency. At a pressure of 22
atmospheres the surface brilliancy had increased to 18 times the
value at one atmosphere pressure. These results were obtained
with impregnated carbons, it having been found impossible to
maintain a "true arc" with pure carbons at pressures greater
than one atmosphere. Further experiments are to be made in
connection with the action of the impregnating salts, the dimen-
sions of the carbons, etc.
In a study38 of metallic arc lamps comparative tests made on
ferro-ilmenite and magnetite cathodes using solid copper anodes
indicate the superiority of the former. A definite dependence was
found between the temperature of the arc and its most efficient
length, shorter arcs being more economical at low amperages and
vice versa. Chromium compounds exercise a cooling effect simi-
lar to that of an excessively long arc. The efficiency of the arc
was increased by amounts varying from 190 to 133 per cent, by
the use of a ferro-ilmenite anode. Indications were that this was
due to the heat resistivity of the material, other anodes of
materials with approximately the same heat resistivity such as
cold rolled steel, vanadium steel and graphite giving similar
favorable results.
On alternating current circuits, arcs between carbon electrodes
and those between metal electrodes act quite differently owing to
the low heat conductivity of carbon. The relighting potential of
carbon electrodes on an alternating current circuit of 50 cycles
and 3 amperes does not exceed 100 volts, but the relighting po-
tential of metal electrodes under identical conditions is almost
equal to a static discharge potential. Experiments have been
made39 using an auxiliary arc to counteract the tendency of
the metal arc to cool down. Combinations were tried of carbon
and ferro-ilmenite electrodes. The results indicated the possi-
bility of using a modification of Duddell's musical-arc circuit for
the purpose of sustaining the alternating ferro-ilmenite arc during
the zero point in the current curve by supplying the necessary
38 Elec. Rev. and W. E., Apr. 10, 1915, p. 691.
33 Elec. Rev. and W. E., May 8, 1915, p. 871.
REPORT OF THE COMMITTEE ON PROGRESS 527
relighting potentials from the circuit itself. It is hoped that a
commercial alternating current metal arc may be thus developed.
An arc40 lamp of an entirely new type is foreshadowed in a
patent issued in England for an arc between tungsten or similar
electrodes enclosed in a bulb containing nitrogen or other inert
gas. The electrodes are horizontal and of small diameter, and
the arc is struck by a simple thermo-mechanical device.
Some recent experiments on the temperature of the mercury
arc as used in work on fluorescence have given results indicating
values as high as 1,400° centigrade. Measurements were made
on the discharge in a tube that had a platinum-iridium thermo-
couple sealed into it with one junction situated at the axis of
the tube. The temperature of 1,400° C. was deduced by extra-
polating about 200° beyond the calibration curve of the thermo-
couple. The investigation suggested that in all probability the
temperatures indicated by a thermo-couple when exposed directly
to the discharge are still very much below that corresponding to
the mean molecular kinetic energy of the luminous vapor.
LAMPS FOR PROJECTION PURPOSES.
Searchlights. — Recently the41 United States Navy has secured
a searchlight of novel form, which has already found application
in Europe. This instrument is 44 inches in diameter and has
instead of the usual silver mirror, a gold mirror which can be
controlled automatically from a distant station. It is claimed
that the use of gold gives a beam of light which is more effective
in showing detail and has greater penetrating power in case of
fog than that coming from a silvered mirror.
In the Swedish army an oxy-acetylene searchlight is being
adopted.42 This apparatus employs a pellet of ceria on which the
oxy-acetylene flame is concentrated. The consumption is stated
to be about 40 liters of acetylene and 40 liters of oxygen per hour
and enough of both is carried with the instrument to provide for
20 hours burning.
A portable searchlight43 has been developed in this country in
which a 20 in. waterproof projector is used with a 750-watt
*" Elec. Bng. (Lond.), May 27, 1915, p. 229.
41 Sci. Amer., Apr. 24, 1915, p. 382.
42 III. Bng. (Lond.), Feb., 1915, p. 84.
43 Elec. Rlwy. Jour., Mar. 27, 1915, p. 639.
528 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
focusing type non- vacuum tungsten lamp. The projector and
battery weigh 600 pounds and are mounted on a two wheeled
carriage. One charge of the battery is designed to give 7 hours
continuous service.
Miner's Lamps. — As a result of the stringent rules of the
British Home Office there has been a steady development in
lamps for use by miners. Six new types have been approved.44
The Bureau of Mines has recently revised its specifications for
miner's lamps under the caption "Schedule 6-A." The principal
changes are in the candlepower rating and in the uniformity test.
Headlights. — A big reduction in power consumption without
reduction in illuminating effect45 in street and surburban railway
headlights has been made possible by the new concentrated fila-
ment tungsten lamps which are replacing arc lamps for this work.
The importance of the problem of the glaring auto headlights
which has caused so much adverse legislation and ill-feeling has
been recognized46 by the Society of Automobile Engineers as
demanding immediate attention. A series of tests have been
worked out which may be used as a standard definition of what
constitutes a dangerous "glare" and the results of such tests will
be submitted to manufacturers of headlights with a view to
eliminating the trouble at the source. Future headlights are to be
constructed according to scientific formulae removing the glare
but thoroughly retaining the far-reaching effect of a searchlight
upon the road itself.
A new method47 of reducing the glare from auto headlights
consists in the use of small curtains mounted on shade rollers
contained in cylinders which may be attached above the lamps.
The shades are raised or lowered by means of cords connected
to a device operated from the driver's seat. When down they
still transmit sufficient light for city driving. Another arrange-
ment48 consists in the mounting of two filaments in one bulb, one
of 4 candlepower for city use, and one of 20 candlepower for
country use. Fittings are now made49 which enable a light to be
" Elec. Eng. (L,ond.), May 6, 1915, p. 197.
45 Elec. Rlu-y. Jour., Mar. 27, 1915, p. 639.
** Sci. Amer., July 17, 1915. P- 59-
"Pop. Mech., Mar., 1915, p. 397.
48 Elec. Rec, Apr., 1915, p. 38.
« Elec. Rec, Feb. 5, 1915, p. 26.
REPORT OF THE COMMITTEE ON PROGRESS 529
mounted almost anywhere on an automobile, even on the wind-
shield or fenders.
Signal Lights. — Fulfilling the forecast made in last year's
report50 semaphores are eliminated in a block signal system now
being installed on one of the large railroad systems.51 White
electric lights are arranged on a black background so that the
three positions of a semaphore can be imitated. Two boards
corresponding to two semaphore arms are used for each track,
the upper corresponding to the stop signal, the lower to the
cautionary signal. These signals are used both by day and night.
The familiar oil lantern carried by train men is being displaced
by an electric lantern52 built along exactly the same lines, a dry
battery being carried in the space formerly occupied by the oil,
and a miniature tungsten lamp furnishing the light. Another
portable lantern for railroad men consists of a nickel plated
casing,53 the top of which carries the battery, the bottom being
flared so as to act as a projector and containing an incandescent
lamp. The lamp is turned on or off by the bail which is made
to snap into the vertical position when being used.
Owing to reckless automobile driving the old "Stop, look and
listen" signs at grade crossings are no longer as efficient as for-
merly in preventing accidents. In consequence one railroad has
inaugurated the use54 of large illuminated billboards to educate
the public in "Safety First" and warn automobilists and others
to use care in crossing tracks. A new type55 of railroad track
warning signal consists of a blackened tube containing a con-
densing lens behind which is a strong incandescent lamp backed
up by a reflector. The tube is mounted so as to point in the
direction from which the motorist will approach and the placing
of the light well back in the tube makes it almost as effective by
day as by night.
Street traffic controlled by means of signal lights described in
last year's report is being tried out56 in Pittsburgh.
There is evidence of the increased use of light as a danger
50 Trans. I. E. S., IX, No. 6, 1914. P- 53°.
61 Pop. Mech., July, 1915, p. 103.
62 Elec. Rec, May, 1915, p. 18.
68 Pop. Mech., June, 1915. P- 893.
M Elec. World, July 17, 1915, p. 146.
M Tech. World, Apr., 1915, p. 226.
M Municipal Jour., Jan. 7, 1915, p. 12.
2
530 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
signal. A power station has installed57 a system of red lamps
on the switchboard gallery which indicate when and where an
individual is entering the compartments containing the dangerous
high tension apparatus. Another central station uses red lights
to indicate that the trolley rail of the ash conveyor is energized
and therefore dangerous.
A novelty58 in the way of a signal and projection light is a
small lamp with a reflector, to be attached to an electric iron.
The lamp is connected to the wiring inside the iron. It not only
illuminates the cloth in front of the iron, but acts as a tell-tale
in case the current is left on when the iron is not being used.
Work is also being done on the development of small59 pilot
lamps for use at the needles of industrial sewing machines.
Flashlights. — Lately there has been an unusual development in
the line of flashlights. One has been brought out exactly60 like
a fountain pen in appearance and size. It is provided with a
pocket slip, is S3A m- 04-6o cm.) long and Y\ in. in diameter,
and weighs only iy2 ounces (42.47 gr.). A modification of this
idea61 includes a pencil holder and the lamp can be operated with
or without the pencil by means of a thumb slide in the pencil
barrel. Still another type62 similar to these employs the clip as
a switch and is provided with a tongue depressor for use by
physicians. A flashlight has also been developed which may63
quickly and easily be attached to an ordinary dry cell.
WAR.
The great war furnishes an opportunity for the study and
an incentive for the development of certain classes of illuminants.
In its activity may be seen the application of the latest ideas
regarding such factors as glare and the power of light of certain
colors to penetrate fog. Active fighting is no more confined to
daylight than business is, and the old type of romantic sorties
under cover of darkness are made almost impossible owing to
the frequent and brilliant flashes of illumination.
57 Elec. World, June 12, 1915, p. 1556.
58 Elec. Mds., June, 1915, p. 165.
59 Elec. World, June 12, 191S. P- 1557-
60 Elec. News (Can.), Mar. 15, 1915, p. 37.
61 Elec. Rec, May, 191 5, p. 18.
62 Elec. World, May 15, 191S, P- 1258.
63 Elec. Rec, June, 1915. p. 21.
REPORT OF THE COMMITTEE ON PROGRESS 53 1
A recently designed signal device consists of a pair of binocu-
lars over which is mounted a small parallel beam flashlight.
The04 battery for lighting the lamp is carried in the belt of the
user. The average range of the instrument is about 3 miles
(4.82 km.). An electric flashlight apparatus used by the British
is similar in size and appearance to an ordinary camera. A
large lens is provided at the front of the box and flashes are
made by means of a telegraph key, which closes the lamp circuit.
Searchlights. — Traveling searchlights have been developed by
the various nations at war.65 Automobile trucks form the car-
riers and supply the power. The lights may be operated either
on the truck or at a distance from it. The French have brought
out a device for distance control employing the response of a
tuning fork at the searchlight to a vibrating current sent from
a contact breaker tuned in unison with the tuning fork. Gilded
mirrors are being used instead of glass. Searchlights are used
not only to detect the movement of the enemy,66 but to blind
troops when they are charging across the zone of fire and to
discomfort the pilots of aeroplanes. Some of those used will
throw an intense light for miles. Owing to the blinding and
confusing effect, it has been found to be impossible to advance
a body of troops in the face of strong searchlights, a practical
illustration of the use and effect of glare.
Illuminants. — Besides searchlights a number of other types of
illuminants are being used.67 Among these may be mentioned
the luminous cartridge which serves for the illumination of
nearby fields and especially for investigating and exploring pur-
poses. It is fired from its own pistol and has a range of action
of about 200 meters and a luminous area of about 100 meters.
It burns from 8 to 10 seconds. Similar to it, but with much
larger luminous activity is the light-rocket which is discharged
from a musket. It is fired distances from 45 to 900 meters and
its intensity is so great that it lights up an area from 500 to 600
meters in diameter with an illumination almost as great as day-
light and lasting from 30 to 40 seconds. Flares have been devel-
M Set. Amer., Oct. 24, 1914, p. 334.
M Elec. World, May 15, 1915, p. 1262.
Sci. Amer. Sup., Oct. 3, 1914, p. 209.
M Sci. Amer. Sup., July 10, 1915, p. 23.
"Jour. f. Gas., May i, 1915, p. 238.
532 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
oped from fireworks and are similar to what are known as red,
white, and blue fires used in Fourth of July celebrations. These
are set out by sappers a distance in front of the battle line and
are controlled from the headquarters of the officers. Ignited at
intervals they keep the battle front illuminated throughout the
night. Star bombs shot from mortars maintain an intense illumi-
nation for intervals as long as 20 minutes. For distance lighting
a projectile similar to shrapnel is used, so constructed that it
furnishes light after a definite time and at a predetermined
height. Air bombs are constructed for use by aeroplanes.
Torches have been developed which burn from 2 to 3 hours.
Profiting by conditions in the European war, the Secretary of
War has directed the Engineering Corps to make an exhaustive
study of and experiments with the use of searchlights, flares,
star bombs, and other lights by troops in the field.
Portable Lamps. — The war has caused a considerable develop-
ment in the way of pocket lamps in Germany.68 In one type of
hand lamp an ingenious mounting of the lamp in conjunction
with a movable screen enables the light to be directed at various
angles with the vertical and still be properly screened from
observation. Another type69 has an arrangement holding a pad
and pencil with the light so concealed that only the pad is illumi-
nated. Still another type70 is in the form of a hemisphere, the
inner surface of which is polished, and with the lamp may be
used as a small searchlight.
Use is being made of acetylene for the illumination of portable
hospitals.71 Limitations in the supply of oil72 have led in Ger-
many to an effort to use coal gas in the lighting* of trains in place
of oil gas previously used. Among the other sources of light
for ordinary purposes used in the war zones should be mentioned
kerosene or paraffin oil lamps with incandescent mantles.73
Safety Lighting. — The danger from night raids by Zeppelins
or other air craft has made it advisable to reduce the lighting in
68 Elek. Zeit., Oct. 22, 1914, p. 1030.
Elek. Ans., Mar. 28, 1915, p. 163.
Elek. Anz., May 9, 191S. P- 240.
69 Elek. Anz., May 16, 1915. P- 254.
70 Elek. Anz., May 23, 1915, P- 269.
71 Pop. Mech., June, 1915, p. 829.
72 Acet. Jour., April, 1915, p. 387.
73 Jour, of Gas Light., June 15, 1915. P- 659.
REPORT OF THE COMMITTEE ON PROGRESS 533
cities and towns in England and France. In Paris74 in the neigh-
borhood of the Eifel tower, lighting has been cut out almost
entirely. As a sample of the orders for reduced lighting used
in London may75 be mentioned the following: In all brightly
lighted streets, squares, and bridges a portion of the lights must
be extinguished so as to break up all conspicuous groups or rows
of lights and the lights not extinguished must be lowered in
intensity, or made invisible from above by shading them or paint-
ing over the tops of the globes, providing that while thick fog
prevails normal lighting may be resumed. Sky signs, illumined
facias, illuminated lettering and powerful lights of all descrip-
tion used for outside advertising or for the illumination of shop
fronts must be extinguished. Subsequently the above orders76
were made more inclusive by prohibiting all lights outside of
shops. This same order called for rear lights on vehicles. It
is interesting to note that while we have had rear light ordi-
nances for years it has taken war conditions to make the desira-
bility of such lights apparent in London. As a result of the
above requirements special reflectors have been developed.77 In
consequence of the lighting conditions it is claimed that there
has been a large increase in fatalities caused by accidents.78
Curious complications have arisen over the question of payment
on the part of shopkeepers for exterior illumination which they
are not receiving.79
Experiments have been made by one of the street car com-
panies of Londonso to meet the requirements of reduced lighting
and still furnish light enough to allow the passengers to read
and conductors to cancel tickets. As a result of these experi-
ments lamp shades used in the lower part of the car are dipped
in a violet lacquer, thereby reducing the illumination by 50 per
cent. In the upper part of the car a similar treatment is given
and the shades arranged so as to throw the light across the car.
'* III. Eng. (Lond.), June, 1915, p. 289.
■ Jour, of Gas Light., Dec. 22, 1914, p. 652.
u Jour, of Gas Light., Dec. 17, 1914, p. 637.
77 Elec. Times, Dec. 31, 1914, p. 609.
" Elec. Times, May 6, 1915, p. 399.
///. Eng.. (I,ond.), July, 1915, p. 300.
'"Jour, of Gas Light., Jan. 26, 1915, p. 182.
80 Elec. Ry. Jour., Dec. 26, 1914, p. 1398.
534 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
The dash lights are covered over with yellow paper. Experi-
ments on dipping the lamps themselves were found to give unsat-
isfactory results.
The restrictive lighting regulations have emphasized the waste
occurring in many show windows81 and the desirability of con-
sidering the principles of illuminating engineering, in order to
get good results. Interesting experiments82 are to be carried out
in London to diminish the inconvenience to the public due to the
low public lighting. Street curb stones are to be painted white
and householders are requested to paint similarly all door steps
leading from sidewalks. Not only in the field of active opera-
tions but also at home83 the question of illumination has been a
matter of vital importance in the various camps formed to take
care of troops newly recruited, or enroute from various parts
of the country. Such camps cover an area of about 250 by 500
yards (228.6 by 457.2 m.) and contain 80 ordinary huts, 27 offi-
cers' huts, dining rooms, guard rooms, etc. About 1,200 lamps
are employed.
The restrictions of lighting in so many towns in England has
retarded the extensive use of the new types of high candlepower,
high efficiency lamps. One of the effects of the war has been the
recognition in Russia of the need of manufacturing her own in-
candescent lamps.84
THE PANAMA-PACIFIC EXPOSITION.
In its use of light the Panama-Pacific Exposition furnishes the
most striking example of the progress of illuminating engineering
that has ever been presented. It is an almost complete report in
itself. For the first time in the history of such institutions a
recognized illuminating engineer has been called in to take care of
that branch of the work. For the first time in history the lighting
of an international exposition was completely designed and
charted before the buildings were erected, and the results bear
eloquent testimony to the wisdom of that action. The latest
types of street lighting both gas and electric are represented ; the
exteriors of the buildings are brilliant with "flood lighting" ; the
lighting of Festival Hall is a unique example of totally indirect
81 Elec, Dec. n, 1915, p. 331.
82 Elec. World, July 17, 1915, p. 158.
83 Elec. Eng. (Lond.), Dec. 24, 1914, p. 649.
84 Elec. Rev. (Lond.), Mar. 12, 1915, p. 346.
REPORT OF THE COMMITTEE ON PROGRESS 535
lighting; display lighting is exemplified in the wonderful scintilla-
tor system and in the Tower of Jewels ; efforts to avoid glare are
manifest on all sides; never has there been a more lavish use of
colored light. And so this exposition stands as a living witness
to the fact that illuminating engineering has "come into its own."
No attempt will be made to discuss all the novelties to be found
in the lighting effects but reference will be made to some of the
more prominent features of the illumination. More complete
descriptions will be found by reference to the partial bibliogra-
phy.85 The basic idea back of the general illumination of the
buildings was the desire to present the exposition at night in the
same relative values of color and perspective in which it is
observed by day. On this account the old outline-system of
illumination in which incandescent electric lamps were used to
outline the architectural features of the buildings was abandoned
in favor of the new flood-lighting idea and particular attention
has been paid to the ocular comfort of the sightseer while at the
same time displaying for his appreciation wonderful effects pro-
duced by artificial light.
Four principal methods of illumination are employed. Op-
posite the walls of the exhibit palaces are luminous art standards
bearing transparent shields, through which light is thrown onto
the fascades. A second method of illumination is found in the
concealed batteries of searchlight projectors which are used to
flood the monumental sculptures, towers and minarets so that the
minutest architectural details are visible. A third source of light-
ing is that of the concealed light which proceeds from the inner
recesses of the columns which encircle the courts or are placed on
the lofty Tower of Jewels and the Italian Towers commanding
the entrance to the Court of Palms and the Court of Flowers.
This method of lighting is also used in the vaults of archways and
in other situations where it is desired to cast light upon the mural
paintings. The great battery of 48 searchlight projectors each
with a 36-in. (91.44 cm.) lens forming the "scintillator" makes a
fourth source of illumination.86
In addition to these four principal sources of lighting there are
85 Light. Jour., Mar., 1915, p. 49.
Elec. World, Feb. 13, 1915, p. 391.
Elec. World, May 29, 1915, p. 1383.
"• Sci. Amer., Apr. 24, 1915, p. 378.
536 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
several minor sources. In various parts of the grounds are
globes of white glass the light from which, at night, dissipates
the shadows under the foliage. In the great central Court of the
Universe two lofty columns of dense white glass are parts of the
two fountains and are the principal source of the night illumin-
ation of the Court.
The striking effect of the Tower of Jewels was obtained
through the use of specially designed87 jewels cut from glass
obtained in Bohemia and having an index of refraction of from
1.68 to 1.7 1. Each gem is suspended so as to be free to swing
with air currents and has a little mirror placed within one-six-
teenth of an inch of the apex, thereby increasing the number
of spectra obtainable.
A noteworthy feature of the highway lighting is the use of 18
to 24-in. (60.96 cm.) globes carrying glassware of an absorption
of approximately 50 per cent, and of a warm opal tint approach-
ing amber. The illumination of the interiors of the buildings is
accomplished by the use of 250 and 500-watt tungsten lamps in
specially designed mirror reflectors. The lamps are located from
40 to 100 ft. (12.19 to 30.48 m.) above the floor, the energy is
less than 2 watts per square foot (9.29 sq. dm.) and the foot-
candles range from ^ to ^ on the floor.
The first commercial installation of high pressure gas lighting
in this country88 and one which is said to show many improve-
ments over foreign practise is to be found in the State and
Foreign Building Section. The main artery for traffic is the
Avenue of Nations and this and other streets and avenues in this
section are lighted by high pressure two-mantle lamps enclosed
in opal globes mounted single on the top of ornamental staff work
columns. The lamps consume 21 cu. ft. (0.59 m.3) of gas per
hour, operate at 3 pounds (1.36 kg.) pressure, reduced at the
standard from 30 pounds, and have a mean spherical candlepower
of 408.
Installations of the same lamps have been made at all the en-
trances and exits of the grounds. At the entrances and exits of
the main group of exhibition palaces and at the entrances of the
courts, lamps of the low pressure type are used, mounted on
87 N. E. L. A. Bui., Apr., 1915, p. 250.
88 Amer. Gas Light. Jour., Nov. 30, 1914, p. 349.
Jour, of Gas Light., July 6, 1915, p. 17.
REPORT OF THE COMMITTEE ON PROGRESS 537
brackets. In the "Zone" gas standards 35 ft. (10.66 m.) high are
placed at intervals of 100 ft. (30.48 m.) on both sides. There
are 72 of these standards each carrying 5-mantle lamps with
mercury valve distance control. Large decorative lanterns are
hung about these lamps. Decorative effects89 are obtained by
the use of gas to produce tongues of flame from serpent-headed
urns.
Some very spectacular effects are obtained90 in the lighting of
the glass dome of the Palace of Horticulture. These effects are
made possible by the use of sets of specially designed lens plates,
color screens and high-powered searchlights. The system used
in lighting the interior of Festival Hall is a separate and distinct
type of interior lighting which is unique. In a pit beneath the
center of the floor are placed a number of searchlights which are
set to throw their beams upward into a diffusing disk of thick
glass sand-blasted on the under side, which distributes the light
over the dome covering the auditorium and the dome in turn acts
as a diffusing reflector.
The most bizarre and spectacular phenomena are produced by
the "scintillator," over 300 effects having been worked out.
At the San Diego Exposition91 neither the "flood-lighting" nor
the "outline" system of illumination is used, but ordinary street
lighting supplemented by light from the arches of the arcades.
This has been found very satisfactory.
STREET LIGHTING.
Display Lighting. — A general survey of the progress in the
lighting of streets shows that there has been a decided increase in
ornamental lighting92 for advertising purposes, or so-called "White
Way" lighting. Among the cities where such installations have
been made during the past year may be mentioned Portland,
Ore.,93 where a system has been placed on one of the business
streets consisting of crossed structural steel arches bridging the
crossings and supported on concrete columns. Each of these
89 Gas Inst. News, Aug., 1915, p. 343.
90 E lee. Rev. and W. E., June 5, 1915, p. 1032.
Sex. Amer., Feb. 20, 1915, p. 180.
91 N. E. L. A. Bui., May, 191 5, p. 340.
Elec. World, Mar. 27, 1915, p. 805.
92 Municipal Jour., June 24, 1915, p. 886.
93 Pop. Mech., July, 1915, p. 101.
538 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
arches is outlined by 192 incandescent lamps placed on the under
side. "White Way" lighting has also been installed in Newark,94
N. J., using lamps of 500 candlepower ; in Louisville,95 Ky. ;
in Lowell,96 Mass., where 234 magnetite 6.6-ampere arc lamps
have been used, placed 14.5 ft. (3.20 m.) above the sidewalk and
with a maximum distance between units of 120 ft. (36.57 m.)
and a minimum of 50 ft. (15.24 m.), lamps being located
as far as possible on alternate sides of the streets ; in Union,97
N. J., where 40 gas-filled, 500-watt tungsten lamps were used; in
Paterson,98 N. J.; in Sioux Falls,99 S. D., where 156 luminous
arc 6.6-ampere lamps have been placed six to a block in a
staggered arrangement; in Sandusky,100 O., where 14 city blocks
are involved and 380 gas-filled tungsten lamps of 250 candlepower
each are mounted on two-light standards approximately 50 ft.
apart; furthermore a complete lighting system for the city is
being installed consisting of 920 60-candlepower and 100-candle-
power lamps of the same type ; in Cleveland, where 600 gas-filled,
20-ampere tungsten lamps are mounted on standards with a
special type of glassware consisting of a refractor to give the
desired distribution of illumination, and an enclosing globe with
roughened surface which is designed to have a pleasing appear-
ance without materially changing the distribution due to the re-
fractor ; in Charleston, W. Va.,101 where 62 ornamental, luminous,
4-ampere arc lamps have been installed; at Malone, N. Y.,102
where 400-candlepower, gas-filled tungsten lamps mounted on
ornamental posts were installed; at St. Cloud, Minn.,103 where
the number of arc lamps was increased to 100 and changed to the
luminous or magnetite type.
There is104 a tendency to depart from the use of five-lamp stand-
ards for "White Way" lighting inasmuch as they are too prom-
inent in the daytime. Preference to-day inclines toward a single
94 Elec. Rev. and W. E., Nov. 14, 1914, p. 954.
95 Elec. Rev. and W . E., Nov. 14, 1914, p. 954.
96 Elec. Rev. and W. E., June 5, 1915, p. 1039.
97 Elec. World, June 26, 1915, p. 1697.
98 Municipal Jour., May 27, 1915, p. 740.
99 Light. Jour. (U.S.), May, 1915, p. 98.
100 Elec. Rev. and W. E., May 22, 1915, p. 963.
101 Municipal Jour., July 22, 1915, p. 114.
102 Elec. Rev. and IV. E., July 31, 1915, p. 180.
103 Municipal Jour., May 27, 1915, p. 729.
104 Elec. World, May 22, 1915. P- 1328.
REPORT OF THE COMMITTEE ON PROGRESS 539
or at most a double-light unit with a comparatively high candle-
power lamp. The introduction of the gas-filled tungsten street
series unit has, in general, resulted in increasing105 the candle-
power used and not in decreasing the wattage. In addition to
the improvement in efficiency the new construction has made
possible an extension in the range of candlepowers available, thus
giving greater flexibility to this type of lighting. The feasibility
of replacing arc lamps with incandescents for street lighting has
been agitated ever since the introduction of incandescent units
of sufficient intensity to produce comparable results. The question
has been re-opened since106 the introduction of the high candle-
power tungsten lamps. Numerous tests have been made and
reports given on the relative merits of the two types of illu-
minants and on the relative cost of operation. But there are so
many factors entering into the problem that it seems increasingly
difficult to draw even general conclusions.
Street lighting progress in various cities,107 aside from the
special ornamental lighting previously mentioned, may be seen
in the following record :
Portland, Ore. — Besides the ornamental lighting previously
mentioned, 150 arc lamps have been added for general street
lighting.
Tacoma, Wash. — Installation has begun on10S 126 new orna-
mental standards each using a 250-watt gas-filled tungsten lamp.
San Francisco, Cal. — A few additional lamps, both gas and
electric arc, have been installed, making a total of 3,423 arc
lamps and 7,838 gas lamps. The most notable improvement has
been the installation of 516 gas-filled, 250-candlepower tungsten
lamps on the main thoroughfare leading to the exposition grounds.
These lamps have been suspended from pipe brackets placed on
the trolley poles, two to a pole, and at a height of 16 ft. (4.87 m.)
above the sidewalk. The distance between poles is approximately
93 ft. (28.34 m.). It is expected that after the close of the ex-
1KN. E. L. A. Bui., Mar., 1915, p. 171.
108 Jour. f. Gas., Aug. 1, 1915, p. 777.
Elec. World, June 19, 1915, p. 1594.
Ibid., July 10, 1915, p. 109.
Elek. u. Masch., Feb. 7, 1915, p. 73.
Elek. Zeit., June 3, 1915, p 269.
1<n Municipal Jour., June 24, 191 5, p. 890.
108 Municipal Jour., May 27, 1915, p. 740.
540 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
position the number of lamps will be cut down as the illumina-
tion is much more brilliant than necessary under ordinary con-
ditions.
Tuscan, Ariz. — A series street-lighting system has recently been
put109 in the business section consisting of 75 five-light stand-
ards equipped with four 60-candlepower and one 100-candle-
power, 6.6-ampere, gas-filled tungsten lamps, and 75 one-light
standards equipped with 100-candlepower similar units.
Dubuque, la. — 585 600-candlepower and 34 400-candlepower
gas-filled tungsten lamps have replaced,110 with a decrease of 20
per cent, in total watt consumption, 470 series alternating current
6-6-ampere arc lamps.
Milwaukee, Wis. — The report on the street lighting survey
authorized in 1914,111 contains among others the following recom-
mendations: that a total of 8,500 lamps be used; on residential
streets 400-candlepower units hung 22.5 ft. (6.24 m.) high on
center suspensions at the street corners, with 100-candlepower
lamps at the curb midway between corners in blocks more than
420 ft. (128.01 m.) long; for business streets a pair of 30- ft.
(9.14 m.) posts on opposite sides of the street every 180 ft.,
each post carrying two 1,000 candlepower lamps, semi-residential
streets to be lighted by 400-candlepower units 360 ft. (109.72 m.)
apart and outlying business streets by 600-candlepower lamps at
the curb and on 180 ft. centers.
Chicago, III. — The principal changes during the112 year have
been the introduction of 300-watt, 20-ampere, gas-filled tungsten
lamps in place of 450-watt enclosed alternating and direct current
arc lamps and in underground work the replacing of 80-watt,
vacuum type tungsten lamps with the 75-watt, 4-ampere series
gas-filled type. The following table shows the number of lamps
in service June 1, 1915, as compared with those in use June
1, 1914:
109 Jour. Elec. Power and Gas, May 22, 1915, p. 407.
110 Elec. World, June 19, 1915, p. 1635.
lu Elec. World, June 27, 1914, p. 1480.
112 Elec. World, May 8, 1915, p. 11 73.
Trans. I. E. S-, Apr. 30, 1915, p. 281.
REPORT OF THE COMMITTEE ON PROGRESS 541
June 1, 1914 June, 1915
Flame arcs 10,283 10,021
300-watt gas-filled tungsten — 9,020
Alternating current enclosed arcs 6,254 1 ,740
Direct current open arcs 1,272 —
4-ampere series vacuum tungsten 4,077 7«I93
Gas, standard type 11,902 10,157
Gas, ornamental type — 730
Gasoline 5,286 4,690
Rented flame arcs 1,161 i,3°2
Indianapolis, Ind. — Five miles of boulevard lighting have been
installed113; io-ampere, gas rilled tungsten lamps have been used,
four 250-candlepower units at the street intersections with 150-
candlepower lamps at irregular intervals between corners and
staggered.
Louisville, Ky. — Two hundred and fifteen gasoline lamps, which
have been in service in the parks and along the parkways and
operated only in the summer, are to be replaced114 by 250 gas-filled,
1 00- watt tungsten lamps which will run throughout the year.
Detroit, Mich. — The lighting system has been extended by the
addition of 1,186 additional 4-ampere, luminous arc lamps as
well as 483 luminous arcs of the 6.6-ampere inverted type. The
latter completes the illumination of eleven miles of boulevard.
Forty series incandescent lamps have been installed in the alleys
of one of the foreign settlements.
Philadelphia, Pa. — Additions during the year include 400 arc
lamps 650 gas-filled, 400- watt tungsten lamps, 179 gasoline lamps
and 300 gas lamps.
New York, N. Y. — Prior to Jan. 1, 1915, Greater New York
was lighted115 wholly by three types of units, the enclosed arc
lamp, the 100-candlepower non-vacuum tungsten lamp and gas
lamps. Since Jan. 1, the 300 to 1,000- watt multiple and 400-
candlepower series type of gas-filled tungsten lamps have replaced
10,000 enclosed carbon and flaming arc lamps. In Queens and
the Bronx about 5,000 non-vacuum 100-candlepower tungsten
units have replaced gas. Approximately110 600, multiple, arc
lamps in use on the bridges connecting the several boroughs have
113 Elec. World, May 8, 1915, p. 1201.
u* Elec. Rev. and W. E., Feb. 20, 1915, p. 332.
115 Light. Jour., May, 1915, p. 108.
118 Elec. World, June 19, 1915, p. 1639.
542 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
been replaced by the 300-watt, gas-filled tungsten units. So far
these lamps have withstood traffic vibrations satisfactorily. Nego-
tiations are under way117 for a large number of 200-watt, non-
vacuum tungsten lamps to replace gas lamps on many of the
side streets.
Brooklyn, N. Y. — All direct current arcs have been replaced
by 300-watt, non-vacuum tungsten lamps. At present, June,
191 5, 2,000 are installed. Gas lamps are being replaced by 300-
watt, non-vacuum tungsten units.
Montreal, Can. — An extension of the lighting system is being
made by118 the addition of 84 luminous, 6.6-ampere, arc lamps, on
ornamental poles of special design placed 125 ft. (48.1 m.) apart.
Canal Zone, Panama. — In the Canal Zone permanent street
lighting systems similar to those in use in Washington, D. C,
are to be installed in119 the principal towns. Gas-filled tungsten
lamps probably of 100-watt size, 6.6-ampere series type will be
used.
Great Britain. — The report120 issued by the British Government
on the use of gas during the year closing June 1, 1914 has been
issued and shows an increase in the number of gas consumers in
Great Britain of 357,411. The report also states that while the
use of electricity for street lighting is increasing there are still
779,442 incandescent gas units in use.
Berlin. — The number of gas lamps in use for public lighting
in Berlin, Mar. 31, 1914, was 43,78c,121 and increase of 2,324. As
in previous years there has been an increase in high pressure light-
ing in the prinicipal streets. In the inner parts of the city, illum-
ination has been strengthened by increasing the number of burn-
ers in a lantern, by increasing the number of many-flame low
pressure inverted lamps, as well as by increasing the number of
lamp standards. In Victoria Park the electric lighting has been
improved by the addition of arc and metal filament lamps. There
are still in use a small number of petroleum and spirit lamps.
Investigations. — The investigation of street lighting being car-
ried on under the joint auspices of committees of the National
117 Cent. Sta., June, 1915, p. 367.
118 Elec. News (Can.), May 1, 1915, p. 39.
119 Light. Jour., Apr., 1915, p. 89.
120 Amer. Gas Lt. Jour., Apr. 5, 1915, p. 217.
m Jour. f. Gas, Mar. 20, 1915, p. 143.
REPORT OF THE COMMITTEE ON PROGRESS 543
Electric Light Association and the Association of Edison Illum-
inating Companies and which was started last year is122 still un-
completed. To properly interpret results already obtained re-
quires a complete knowledge of the conditions and no attempt will
be made to summarize them in this report. Another investigation
of the factors connected with effective illumination of streets has
been directed toward a study of the effect of glare on visual
acuity. The method123 of test consisted in making observations
of a special visual acuity test chart first with the street lamps off
and then under ordinary lighting conditions. Among the con-
clusions reached were that merely surrounding a brilliant source
of light by a diffusing globe does not materially diminish blinding
effects. Mounting heights less than 20 ft. (6.09 m.) should be
avoided if possible and heights less than 15 ft. should never be
employed. When the height is relatively low, the candlepower
between the angles of 65 ° and 900 from the vertical should also
be relatively low. So far as avoidance of glare is concerned
there is no object in increasing the height beyond 50 ft.
(15.24 m.). An excellent summary of technical data on electric
street illuminants was presented at the 191 5 convention of the
National Electric Light Association.
OTHER EXTERIOR ILLUMINATION.
The continued improvement in illuminants is reflected in the
spread of out-door-lighting of all kinds and the use of light more
than ever before for a variety of purposes. Thus a real estate
dealer arranges to have a new sub-division highly illuminated12*
and rapidly sells his lots to customers who have come out to
view them at night. Improvements in distance lighting and con-
trol125 have made feasible the employment of gas in places where
its use had previously been considered impossible. A big exten-
sion is to be noted in the use of light for exterior advertising
purposes.
Flood-lighting. — One of the most striking illustrations of the
modern "flood-lighting" method of illuminating the exterior of
122 Trans. I. E. S., 9, 1914, P- 536.
Report of Committee on St. Light. N. B. L. A., June, 1915. See also Trans.
A. I. B. B., July, 1915, p. 1379.
123 Elec. Rev. and W. B., Mar. 6, 1915, p. 439.
124 Elec. Rev. and W. B., May 8, 1915, p. 856.
123 Gas Age, July 1, 1915, p. 5.
544 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
buildings is to be found in the lighting of the Woolworth build-
ing120 in New York City, which was disclosed to public view at
the beginning of the year. It has been said that more light is
provided for the illumination of the tower than is usually em-
ployed in lighting a city of 30,000 inhabitants. 600 automobile
projector units fitted with 250- watt, gas-filled tungsten lamps are
used to throw light on the structure from the thirtieth to the
fifty-eighth story. These projectors are arranged so that some
throw their light upward and the rest throw their light down-
ward. Thus there is one continuous diffusion of light over the
whole surface. The lamps throwing light downward are care-
fully screened so as not to be directly visible from the street.
The most novel point of the installation, however, is at the six-
tieth story called the "crow's-nest" or "lantern." It has been en-
closed with diffusing glass and within are placed twenty-four
1,000-watt lamps. An automobile dimmer connected with these
lamps continuously alters their intensity in an irregular cycle.
Thus at one instant the glass surface of the lantern shows a deep
red glow no brighter than the adjacent gilded structure, and
again it flares up to a bright white light many times this bright-
ness and visible for miles.
The flood-lighting idea has been much extended in127 the illum-
ination of advertising signs on billboards, water tanks, roofs of
buildings, side walls and elsewhere. In such cases the effect is
accomplished by directing a beam of light against the sign from
some nearby convenient location; a new lighting unit of high
intensity utilizing a parabolic reflector has been recently developed
for this special purpose.
Lighting of Sports. — The lighting of courts for tennis and
other sports has proved so satisfactory that the idea is being tried
out in a number of different ways. A playground in a city park
has been illuminated so that128 its various amusements are avail-
able at night as well as by day. Five 750-watt, gas-filled tungsten
lamps are used to light the football field while 1,000-watt units
are used to illuminate the swings and gymnasium apparatus.
These units are placed 20 ft. (6.09 m.) above the ground on
goose-neck boulevard posts. A test was made at the Indiana
126 Elec. Rev. and W. E., June 5, 1915, p. 1048.
121 Elec. Merchandise, Dec, 1915, p. 306. See also Cent. Sta., May, 1915, p. 346.
128 Elec. World, May 22, 1915, p. 1328.
REPORT OF THE COMMITTEE ON PROGRESS 545
State Fair grounds recently of129 a system of illumination, in
order to try out the practicability of automobile racing at night.
The result was a complete success. Lights of the type used in
contracting and railroad work for emergency operations at night,
were placed at intervals about the track. Each light was sup-
plied from its own cylinder of dissolved acetylene. In another
case130 an outdoor skating rink used for the sport of curling has
been lighted by tungsten lamps installed on two lines of stray
wires, extending the length of the rink, and about 35 ft. (10.66 m.)
apart. Extra illumination is furnished at the ends over the goals.
The lamps hang about 15 ft. above the surface of the ice.
A sign of progress131 is to be noted in the installation of a
lighting system on the celebrated wall which surrounds the block
in Salt Lake City enclosing the famous Tabernacle and Temple.
The wall is approximately 12 ft. (3.65 m.) high and will be
lighted by high power lamps located every 50 ft. (15.24 m.).
Because of the scarcity of kerosene there has been an exten-
sion of gas and electric lighting in Germany,132 alcohol and acety-
lene being adopted in the country districts.
INTERIOR ILLUMINATION.
The trend in interior lighting continues to be in the direction
of protecting the eyes from excessive brightness.
Hotel Lighting. — A recently finished, and133 what is claimed to
be largest hotel in Europe, has been fitted throughout with the
semi-indirect system of illumination. The lighting has been so
arranged that corridor lights are independent of those in adjacent
bed-rooms. In the dome of the rotunda court a novel plan has
been adopted of introducing opal bulls-eyes, with a lamp behind
each, into the risers which support the glazing of the dome.
Around the dome cornice is a ring of lamps which are concealed
from view at the floor level but throw a considerable volume of
light upward into the dome. Some 6,000 lamps are used in
this hotel. In England134 the use of high pressure gas is being
extended to factory lighting.
129 So'. Amer., June 12, 1915, p. 587.
130 Blec. Rev. and W. E., Feb. 13, 1915, p. 311.
131 Elec. Merchandise, Apr., 1915, p. 82.
132 Pop. Mech., May, 1915, p. 651.
133 Elec. Times, June 24, 1915, p. 531.
134 Jour, of Gas. Lt., June 1, 1915, p. 506.
3
546 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
Municipal Buildings. — While a private enterprise is quick to
see and adopt improvements in lighting sources and methods, the
municipally controlled institution has in the past exhibited a
decided inertia in this respect. A start has been made in Boston135
to remedy this and the replacement of old types of lamps of low
efficiency has already brought about a marked saving to the city.
The change has been so satisfactory that one of the city engineers
is to devote his entire time during this year to improving the
lighting of buildings in the school, police and fire departments.
Office Buildings. — Heavy glass partitions which are translucent,
substantial, sun-proof, and fire-proof, are being introduced as a136
means of distributing sunlight through large office buildings,
without lessening the privacy of the various offices. These par-
titions are built of clear glass units, 2 in. (50.8 mm.) thick, and
either 6 or 8 in. square, which are reduced to translucency by
impressed designs.
Hospitals. — That the educational work of the Society on the
subject of color and glare is bearing fruit, is seen in the use of
green and buff for the color of the walls in a large Western137
hospital. White had always been used, but it was found, on
trial, that the discomfort coming from the necessity of eye-
adaptation on the part of surgeons looking up from their work,
and seeing only white-clothed assistants and white walls was
largely eliminated with the use of other colors. The effect on
patients has also been beneficial. In another large city hospital
a rather unique use of the mercury-vapor lamp is found in its
employment138 for examination of X-ray skyographs.
Street Railway Cars. — A growing recognition of the importance
of proper lighting in every sphere of activity is illustrated in
the139 recent extensive tests conducted by a large municipal rail-
way. A full sized template car was built and tested when
equipped with direct, semi-indirect, and totally indirect systems
of lighting. The general effect and appearance of each system
under test were judged by comparison with present methods of
car lighting for similar service. The effect of the light on the
135 Elec. World, May 22, 1915, p. 1327.
136 Pop. Mech., June, 1915, p. 818.
13T Pop. Elec. and Mod. Mech., Dec, 1914, p. 644.
138 Elec. World, June 5, 1915, p. 1475.
139 Trans. I. E- S., 1915, p. 227.
REPORT OF THE COMMITTEE ON PROGRESS 547
eyes was particularly noted by a large number of observers. The
system finally adopted consists of a single row of 56-watt, bowl-
frosted tungsten lamps placed symmetrically down the center
line and equipped with opal glass reflectors. These lamps were
supplemented by six 10-watt, all-frosted round bulb tungsten
emergency lamps. One big unit was placed on each end-bulkhead
of the car to bring up the illumination at these points. In the car
as finally equipped the illumination averaged 5.94 foot-candles, at
normal and 3.85 at 85 per cent, voltage, the energy consumption
was 1.44 watts per square foot, effective lumens per watt 4.14 and
the utilized efficiency 50.6 per cent.
Another street railway company is emphasizing140 the "Safety
First" principle by providing a light so placed as to directly
illuminate the step of the street car. A practical application of
signal lights has been adopted by141 some of the theaters of
Vienna. On the back of each seat is a small electric lamp which
illuminates the seat number. As long as the seat is turned up,
as it usually is when not occupied, the light is burning, but is
shut off when the seat is turned down. By this means the use of
ushers has been materially decreased.
Clock Tower. — A novel use for the method of indirect lighting
is to be found in the illumination of clock dials in the new Boston
Custom House.142 Behind each dial is a chamber with white
walls illuminated by a number of lamps. Numerals of the dial
are in the form of slots set in concrete and the lights in each
chamber are so arranged that no unreflected light passes through
the slot. The effect is to make each numeral appear as if cut
out from a piece of uniformly lighted paper.
An application of the "flood-lighting" idea was made143 recently
at one of the automobile shows where a machine was brilliantly
illuminated by lights in two ornamental troughs hung by chains
about 8 ft. from the floor, and 9 ft. (2.74 m.) in front of the car.
The art-glass dome is ordinarily associated only with the light-
ing of dining-rooms, but it has been added144 to the long list of
140 Elec. Ry. Jour., Jan. 30, 1915, p. 247.
141 Pop. Mech., Apr., 1915, p. 568.
142 Pop. Mech., July, 1915, p. 75.
143 Elec. World, May 15, 1915, p. 1255.
144 Elec. World, May 22, 1915, p. 1315.
548 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
illuminants used to produce an attractive show window illumin-
ation.
Reflection. — Now that semi-indirect and totally indirect light-
ing systems are coming more and more into use, the effect of the
walls and ceilings in reflecting light is of great importance. The
results of considerable work on tests of the reflecting power of
paints have been presented. The145 colors examined ranged from
white to dark buffs and greens. The highest coefficient obtained
was 0.657 which was for a white oil paint of medium gloss. Less
than one half of the samples tested showed coefficients above 50
per cent, and all of those that did so were of very light creamy
or yellowish tones. A rather light olive color gave only 0.328.
Code. — Reference should be made to the very important work
of the Committee on Lighting Legislation and the Factory Light-
ing Committee of this society, as a result of which a code on the
lighting of factories, mills and work-places has been prepared.
GLOBES, REFLECTORS AND FIXTURES.
Having plenty of light available either from gas or electricity,
manufacturers have increased the variety of materials used in
making globes, reflectors and shades. At one extreme might be
put the wicker basket. Provided with or without a lining, it
is used suspended from the ceiling as a semi-indirect fixture ; or
inverted and covered with suitable material, it makes a shade for
a table lamp. At the other extreme might be put the hammered
brass bowl with or without glass inserts and used for either totally
indirect or semi-indirect lighting. There is a growing use of
floor lamps having very large shades and mounted on standards
5 or 6 ft. (1.52 or 1.82 m.) high. Such a lamp is replacing the
old center table lamp for family reading and inasmuch as those
using it can all have the light properly directed for reading pur-
poses, it forms a step in the direction of eye protection. There
is also a growing trend on the146 part of architects to call for
lighting fixtures which conform to the period of their surround-
ings.
In school rooms an increasing tendency toward the use of
denser glassware with the semi-indirect lighting method is notice-
able and in general for both direct and semi-indirect system the
145 Blec. World, Jan. 23, 191s, P- 211.
146 Elec. World, Apr. 3, 1915, p. 87:1.
REPORT OF THE COMMITTEE ON PROGRESS 549
denser glassware is used. Furthermore the tendency towards
constantly increasing candlepower in small units has led to a
greater use of diffusing media such as marble and alabaster, and
to fixtures carrying several lights burning upright with small
semi-indirect shades. The use of cloth for shades is growing
and an umbrella manufacturer has developed147 a collapsible
shade of cretonne, which can be foiled up, when not in use, for
packing or storage purposes.
A novel arrangement has been brought out in England148 for
converting a dining room fixture into a combined direct and semi-
indirect unit. A double cone of white silk is employed in con-
junction with the common "corona band" so that the lamp occu-
pies a position in the lower cone, when the fitting is at the usual
height, giving light directly downward, while at another height
the lamp moves up into the upper cone, with the light directed
toward the ceiling.
For the modern very large office building an equipment of
specially designed fixtures is not uncommon. In one case of this
kind149 a fixture was developed which can be utilized either for
direct, semi-indirect or totally indirect lighting. There is evi-
dence150 of a considerable increase in the employment of the semi-
indirect type of fixtures for gas.
A great advance has been made in gas fittings.151 The old
"goose neck," fastened with a wire, is being replaced by straight
pipe tubing with gas-tight adjustable couplings, which make a
variety of brackets available.
Reflectors have been developed for converting152 the ordinary
gas "arc" as used in stores and warehouses into a semi-indirect
unit, thus meeting the demand for this type of lighting without
the necessity of scrapping former fixtures. The advent of the
100-watt, gas-filled tungsten unit has caused the development
of prismatic and mirrored reflectors for use in show-window
lighting.
147 Light. Jour, and Eng. (Lond.), Feb., 1915, p. 81.
""///. Eng. (Lond.), Mar., 1915, p. 103.
149 Elec. World, Feb. 20, 1915, p. 490.
150 The Gas Age, Jan. 1, 1915, p. 8.
151 Light. Jour. (U.S.), Dec, 1914, p. 281.
Proc. Amer. Gas Inst., vol. IX, 1914, p. 886.
132 Amer. Gas Lt. Jour., May 3, 1915, p. 286.
550 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
In lighting fixtures of ornate design and equipped with electric
candle or candelabra lamps the use of ordinary key or pull sockets
for individual lamp control is often undesirable and esthetically
objectionable. A rotating switch has been devised to meet153 this
condition, which is operated by turning an outer sleeve forming
part of the candle. The replacing of arc lamps by the new high
efficiency tungsten lamps has resulted in an154 adaptation of the
fixtures of the former to act as housings for the latter. The prin-
cipal change needed is the introduction of baffle plates to prevent
the entrance of rain without hindering the ventilation. For all
classes of outdoor lighting by electricity, fixtures have been de-
signed which include155 not only adaptability to series or multiple
circuits, to pole or cross-span suspension, but also ventilating and
enclosing glassware if desired, so that a complete equipment is
available in one fixture.
A reinforced-concrete lighting standard of attractive design
and appearance is being installed156 in a number of California
cities including beach resorts, where metal standards have suf-
ered severely in the past owing to the action of salt air.
PHOTOMETRY.
The measurement of light sources differing in color value con-
tinues to interest the photometrist. Developments have followed
two general lines, one the elimination of the color difference,
thereby reducing conditions to those of ordinary photometry, the
other the use of the flicker photometer which has not yet been
generally accepted as a solution of the problem.
Secondary Standards. — At the National Physical Laboratory
in England there has been completed and described157 a careful
and exhaustive research having for its object the establishment of
a set of standards matching in color lamps operating at the
various efficiencies in ordinary use. In this research the color
problem was met by using the so-called "Cascade" method in
which a lamp at a given watts per candle is measured against one
whose watts per candle differs by an amount which will make the
153 Blec. Rev. and W. B., May 29, 1915, p. 1005.
154 Elec. World, May 1, 1915, p. 1131.
155 B lee. Rev. and W. B., July 24, 1915, p. 167.
16a Elec. World, Apr. 3, 1915, p. 874.
151 Phil. Mag., July, 1915, p. 63.
REPORT OF THE COMMITTEE ON PROGRESS 55 1
color difference small enough not to be objectionable. Check
measurements were also made in which the maximum color diff-
erence was encountered. The experience gained from these and
other comparisons was that whereas an observer may be relied
upon for constancy of judgment in measuring with an ordinary
contrast photometer sources differing by a small amount in color
value, the same constancy in judgment was not obtainable where
the color differences were large. Efforts were made to use the
flicker photometer but the results were not satisfactory and the
accuracy was of a different order of magnitude from that found
with the other method.
Color Difference. — It is rather interesting to note that else-
where158 in observations on color differences made with a flicker
photometer and extending over a year, individual observers re-
produced their results with very few exceptions.
The color screen method of eliminating the color difference in
heterchromatic photomery has been extended by the develop-
ment159 of a blue solution, which in varying degrees of satura-
tion will provide a color match between a standard carbon lamp
and another lamp operating at any watts per candle from 3.1
to 0.5. An alternative for160 the color absorbing solution in
eliminating color differences is suggested in a new photometer
using polarized light. It is based on the rotation of the plane
of polarization by a quartz plate and the fact that this rotation is
different for light of different wave-lengths.
Flicker. — By applying to a modified form of the Conroy pho-
tometer161 an oscillating platinized mirror and adding an optical
wedge having its density gradient vertical and different by two
per cent, from top to bottom a new flicker-photometer has been
developed. Another arrangement162 for a flicker-photometer
consists in a modification applicable to the ordinary Lummer-
Brodhun photometer head. A tube, replacing the ordinary eye-
piece, carries a rotating prism. Means are provided for illumin-
ating the surrounding field and for accurate speed control.
m Trans. I. E. S"., Apr. 30, 1915, p. 207.
"•Trans. I. E. S., Apr. 30, 1915, p. 253.
lv> Phys. Rev., July, 1915, p. 64.
181 Phys. Rev., 4, 1914, p. 477.
142 Light. Jow., May, 1915, p. 1 11.
552 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
A theory of the flicker-photometer has been presented in163
which the behavior of the instrument is deduced directly from the
relationship of critical freqency and illumination. It is assumed
that a fluctuating stimulus is transmitted as a considerably
dampened fluctuating impression whose form and amplitude can
be calculated by using the Fourier linear diffusion equation. The
same line of reasoning is used to explain the relationship of color
flicker to brightness flicker. Further work164 has also been done
on the question whether results in color photometry obtained by
the flicker method and the acuteness of vision method are the
same. The data obtained in these experiments indicated they
are. A Lummer-Pringsheim spectro-flicker-photometer was em-
ployed and experiments made with foveal vision and portions of
the retina lying 20° to 300 outside the direct line of sight. Means
have been provided,105 using colored absorbing media for correct-
ing an abnormal eye. It is claimed that by the practical applica-
tion of this method to the flicker-photometer it is possible to equip
any observer so that he will read correctly color differences of a
given type ; and to equip a color blind observer so that he will not
only read such differences correctly, but also measure other color
differences with no more uncertainty than a random observer of
"normal" vision will do.
Integrating Sphere. — At the last convention there was quite a
discussion on the best paint to use for the inner diffusing surface
of an integrating sphere. An elaborate research was undertaken in
Germany166 to decide not only this point but also the best material
of which to make the sphere itself. The results indicated that
iron plate is to be preferred to zinc for the construction material
and that zinc white as the diffusing surface gives the best results.
New Instruments. — In the photometry of phosphorescent gases
and certain phosphorescent solids, the light to be measured is of
rapidly diminishing intensity. In order to ascertain the errors
occurring in the measurement of such a light a modification of
the ordinary photometer has been devised167 in which the essential
feature is a sliding carriage supporting one of the lamps and
163 Phil. Mag., May 28, 1915, p. 708.
184 Ann. d. Phys., Aug. 14, 1914, p. 105.
165 Trans. I. E- S., Apr. 30, 1915, p. 259.
166 Elek. Zeit., Mar. 25, 1915, p. 37-
107 Phys. Rev., Oct., 1914, p. 289.
REPORT OF THE COMMITTEE ON PROGRESS 553
capable of being set in to and fro motion at uniform velocity in
the photometric axis. Means are provided for recording the
position of the carriage while in motion. Using this instrument
an investigation showed that errors as high as 15 per cent, or
more, and apparently due to retinal fatigue, may occur in the
photometric measurement or phosphorescent decays.
A new portable illumination photometer has been brought
out168 which is a modification of the Weber type and much more
compact. Another illuminometer169 has been described for use
where rapid and rough measurements of light intensity are
desired. In this instrument a screen of black silk illuminated
from the rear is viewed in comparison with tinted sectors, on
which falls the illumination to be measured. The intensity of
the light from the comparison lamp is controlled by an iris
diaphragm. As a quick means of determining the various energy
relations in tungsten lamps, a direct reading instrument has been
devised170 using data presented at the last convention.171 It is
made up of volts, watts per candle and per cent, candlepower
scales. The volt scale has a range from 94 to 166 volts, while the
watts-per-candle scale limits are 0.70 and 2.05. Knowing any
two relations the other may be calculated within the range of the
instrument.
A study172 of the rotating sectored disk when used in pho-
tographic photometry has shown that an intermittent exposure,
such as that given by the disk, has the same integral effect as a
continuous exposure for the same period. The conclusion for
ultra-violet radiation is the same as that found for visible radi-
ation. Experiments were made on a variety of plates and it was
found that the results were independent, within wide limits of the
rate of rotation of the sector and of the period of exposure.
Gas-filled Tungsten Lamps. — The measurement of the candle-
power of the gas-filled tungsten lamps has developed some entirely
new problems in photometry. Thus it was early discovered173
that both the watts consumed and the candlepower of the lamp
vary when the lamp is rotated at different speeds. One set of
168 Elec. World, Jan. 9, 1915, p. 85.
169 Elec. World, Jan. 16, 1915, p. 170.
110 Jour, of Frank. Inst., July, 1915, p. 102.
171 Trans. I. E. S., 9, 1914, p. 734.
172 Ann. d. Phys., Nov. 3, 1914, p. 801.
173 Trans. I. E. R, 9, i9i4, p. i024.
554 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
experiments174 showed that for any change in speed, while the
change in candlepower was roughly ten times the change in cur-
rent but always in the opposite direction, and regardless of the
position of the lamp, the absolute change in candlepower with
the lamp in the position of tip up is about twice the change with
the tip down and similarly for the absolute change in the current.
From the photometric standpoint a favorable condition was dis-
covered in that, for a given position of the lamp, the current and
therefore the candlepower return to the stationary value at the
same speed. If then, a gas-filled lamp is photometered in the
position tip down, while rotating at the particular speed which
gives the same current value as when the lamp is stationary, the
mean horizontal candlepower as measured will be free from
errors due to rotation.
Various explanations have been offered for these phenomena.
It has been suggested that they may be due to variations in the
contacts between the filaments and the anchor wires ; to changes
in the currents of gas about the filament; to the lengthening of
the helically coiled173 filament, thus changing its resistance; to a
cooling effect due to the action of the external air in the bulb.
Photo-electric Cell. — In astronomical photometry176 work is
being done, with some success, looking toward increasing the sen-
sibility of the photo-electric cell. A null method of using photo-
electric cells has been devised which,177 it is claimed, does away
with the so-called "dark current" without in the least reducing
the sensitivity.
Pentane Standard. — A redetermination at the National Phys-
ical Laboratory178 of the constants of the Pentane lamp gave the
following as the equation of the candlepower :
C.P. = ( (I -f 0.0063 (8 — <?) — o.ooo85 (760 — b) )
e being the humidity in liters of water vapor per cubic meter of
moist air, and b the barometric pressure in millimeters. Evi-
dence was obtained that there exists a temperature coefficient in
the case of the pentane lamp, a point which had been raised pre-
viously at the Bureau of Standards. Apparently the temperature
174 Elec. World, Dec. 26, 1914, p. 1248.
175 E lee. World, Jan. 9, 1915, p. 78.
176 Science, June 4, 1915, p. 810.
177 Phys. Rev., July, 1915, p. 66.
178 Phil. Mag., July, 1915, p. 80.
REPORT OF THE COMMITTEE ON PROGRESS 555
and humidity effects act against one another and in practise it
is the difference between the two which is operative. It is sug-
gested that if work of the very highest accuracy is to be carried
out with flame standards under abnormal humidity conditions,
the combined humidity temperature coefficient should be deter-
mined for the locality in which the work is to be conducted.
Radiation. — Experiments179 on the emissivity of metals at high
temperatures have given results indicating a change in the
emissivity of platinum for wave-length A = 0.65/a. This fact if
verified would influence the constancy of the Violle standard of
light.
Two investigations have been made during the year on the
determination of the visibility of radiant energy. One covered180
the whole visible spectrum going further into the red and voilet
than heretofore. The other181 dealt with the red end of the
spectrum only, results being obtained out as far as A = 0.770/i.
Calculation. — Methods of calculating the illumination produced
by a direct-lighting source are numerous and well known. But
in the case of a totally indirect or semi-indirect unit the calcula-
tion is decidedly modified. A method has been proposed182 in
which it is necessary to know only the photometric curve, the
coefficient of reflection for the secondary source (usually the
ceiling), the distance of the unit below the ceiling and the height
of the ceiling above the plane of illumination. Roughly the
method involves the consideration of the ceiling as a secondary
light source considered as made up of a series of circular annuli
or rings of uniform intensity of illumination. The effect of each
ring is calculated independently.
Nomenclature. — Considerable attention has been given to the
subject of nomenclature during the past year. It has been pro-
posed183 that the word "lambert" be used in referring to bright-
ness in lumens per unit projected area. The "lambert" is inter-
preted as the equivalent in appearance to the eye of a surface
source emitting one lumen per unit area in accordance with
Lambert's cosine law. The following resolution which was sub-
178 Phys . Rev., Dec, 1914, p. 547.
180 Phil. Mag., Feb., 1915, p. 301.
181 Phys. Rev., July, 1915, p. 68.
182 Elec. World, June 5, 1915, p. 1463.
183 Elec. World, Mar. 29, 1915, p. 715.
556 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
mitted by the Committee on Nomenclature and Standards has
been approved184 by the Council of the Society :
Resolved, That it is the opinion of this Committee
(a) That the output of all illuminants should be expressed in
lumens.
(b) That illuminants should be rated upon a lumen basis instead
of a candlepower basis.
(c) That the specific output of electric lamps should be stated in
lumens per watt and the specific output of illuminants
dependent upon combustion should be stated in lumens per
British thermal unit per hour.
PHOTOGRAPHY.
Sources. — The use of gas light185 for taking pictures is increas-
ing and special mantles have been designed for the purpose. In
order to facilitate the use of the high intensity gas-filled tungsten
lamp186 in photographic portrait studios, a colored glass screen
has been developed which reduces the luminous intensity of the
light to one-third its ordinary value without appreciably reducing
the actinic value for ordinary plates. For convenience this glass
has been incorporated in the lamp bulb. Thus high candlepower
lamps may be used without producing an uncomfortable glare.
It has been found possible187 to use such lamps, screened as
described, in moving picture production studios. In a big
western moving picture plantls8 there is used a combination of
mercury-vapor lamps and 2,000-candlepower tungsten gas-filled
units of the type just mentioned. In Germany189 tests have been
made on the use of the gas-filled tungsten lamp for photographic
work at voltages higher than normal, thus giving greater actinic
value. This same idea has been proposed and experimented
on190 in this country.
Tests have been made on191 the density of the photographic
image produced under fixed conditions of distance and time by
184 Trans. I. E. S., 9, p. 2, 1914.
185 Gas Age, Mar. 15, 1915, p. 304.
Light. Jour. (U. S.), Dec, 1915. P- 281.
Proc. Amer. Gas Inst., vol. 9, 1914, p. 886.
186 Elec. World, Nov. 14, 1914. P- 95°.
187 Trans. I. E. S., No. 2, 1915, p. 166.
188 Elec. World, July 17, 1915. P- 137-
189 Zeit. f. Beleu., Mar., 1915, p. 33.
190 Elec. World, Nov. 14, 1914, p. 950.
191 Elec. World, Nov. 14, 191 4, p. 95 6.
REPORT OF THE COMMITTEE ON PROGRESS 557
the light from different types of arc lamps under various condi-
tions. The lamps tested were of the alternating current and
direct current enclosed carbon and flaming arc types operated at
various currents. The results showed that the highest actinic
efficiency was obtained by the 220- volt, enclosed carbon arc ; next
in value were respectively, the alternating current and direct cur-
rent no-volt, flaming arcs with electrodes designed particularly
for photographic work.
A photographic paper has been developed192 on which portraits
may be reproduced directly without the preparation of the usual
negative. For operation with artificial illuminants the paper is
treated with a dye which makes it more sensitive to yellow light.
The pictures are mirror images of the original.
LEGISLATION.
Calorific Standard. — The Illinois Commission has ruled193 that
in all parts of the state excepting Chicago a calorific standard of
565 B. t. u. for gas shall be used. Chicago is to remain under
the candlepower standard. The calorific standard has been
adopted by the Maryland Public Service Commission.194 A heat-
ing value of 600 B. t. u. is specified. It was estimated by the
Commission that in the state generally only 6 to 10 per cent, of
the gas used is burned in flat flame burners. The use of the
calorific standard in gas undertakings does not seem to be grow-
ing rapidly in England.195 Only eight companies have applied
for parliamentary authority during the session of 1915. Four
of these companies applied for a 500 B. t. u. standard.
Glare. — Extremely bright lamps are no longer allowed on resi-
dential streets, especially in front of isolated stores, in Washing-
ton, D. C.196 Regulations adopted prohibit the use of lamps
exceeding 100 candlepower on streets other than business streets.
They also require a minimum height of 15 ft. (4.57 m.) for all
private lamps supported from sidewalks, and that such lamps
are to be enclosed in opalescent globes in order that the eyes of
passers-by shall be protected from glare.
192 Elec. World, Jan. 16, 1915, p. 190.
193 Proc. Amer. Gas Inst., vol. 9, 1914, p. 373.
194 Jour, of Gas Light., May 24, 1915, p. 463.
ias Amer. Gas Light Jour., Feb. i, 1915, p. 73.
1M Elec. World, Oct. 10, 1914, p. 700.
558 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
In December last197 the War Department issued regulations
ordering all fishing fields to be protected by a marine lantern of
recent invention using acetylene as the illuminant. These lan-
terns, capable of 23 days' service, are arranged to give an in-shore
and out-shore light to warn vessels that the areas thereabout
comprise fishing pounds and are not open to navigation. Already
a number of these lights have been placed.
A bill has been introduced198 in the Utah legislature providing
for the creation of special lighting improvement districts, under
which the property owners on any street or sub-division may
petition the city commission to create such districts and to install
therein lighting systems.
Safety. — The Ottawa (Canada) City Council have recently199
taken up the matter of all-night lighting of public buildings used
for residence purposes. A by-law has been passed providing that
the stairs, halls and corridors of all apartment houses, hotel and
lodging houses must be lighted from sunset to sunrise.
In places where public safety demands it, there is a growing
tendency on the part of municipal authorities to require two
independent systems of illumination so that in case of failures
on the part of either the other will be available.
Headlights. — The Public Service Commission of Vermont has
issued an order200 concerning the use of headlights on locomotives.
Railroad corporations doing business within the state are required
to equip engines with headlights of not less than 2,500 apparent
beam candlepower when measured with the aid of a reflector,
rated in accordance with the average of the center readings
between 500 and 1,000 ft. (304.80 m.) ahead and upon a refer-
ence plane 3 ft. (0.91 m.) above the rails. In Nevada an amend-
ment to the electric headlight law has been passed,201 providing
that any electric headlight "which will pick up and distinguish an
object the size of a man dressed in dark clothing on a dark and
clear night at 1,000 ft." will be deemed equivalent to a 1,500-
candlepower headlight measured without reflector. Legislation
187 Acet. Jour., Feb., 1915, p. 305.
198 Elec. Rev. and W. E., Feb. 27, 1915, p. 376.
199 Elec. News (Can.), Apr. 1, 1915, p. 38.
200 Railway Age Gazette, Jan. 22, 1915, p. 127.
201 Raihvay Age Gazette, Jan. 22, 1915, p. 123.
REPORT OE THE COMMITTEE ON PROGRESS 559
regarding headlights for motor vehicles has also been passed in
New Jersey.
ILLUMINATING ENGINEERING IN GENERAL.
Daylight Saving. — By adopting eastern standard time Cleve-
land, Ohio has added one hour to the period of daylight. The
result202 has caused a renewed interest in the so-called "daylight
saving movement" in the middle west. In Holland also this move-
ment is being agitated.20'1
The use of light sources imitating daylight is growing204 and
has been found advantageous not only in clothing, painting and
wall paper stores and factories, but also in printing and litho-
graphing establishments, paper mills, oil refining plants, cigar
factories, etc.
It has been proposed205 to add to the numerous collections in
Berlin a museum of illuminating appliances in which the devel-
opment from the 17th century of lamps and other devices for
street lighting will be shown.
Luminous Efficiency. — Values of the radiant luminous ef-
ficiencies (ratio of the energy radiated evaluated according to its
effectiveness in producing the sensation of light to the total energy
radiated) of various light sources have been determined using the
method which employs an absorbing solution whose transmission
curve is the same as the luminosity curve of the eye.206 Among
the results obtained were :
4 w.p.c. carbon lamp 0.43
0.8-ampere Nernst filament 1.08
6.6-ampere gas-filled tungsten at 0.65 w.p.c 2.93
Ordinary vacuum tungsten at 1 w.p.c i-99
Open burner, gas 0.9
Incandescent mantle, gas 0.5 to 1.2
1.7 ampere mercury arc, Pfund type 30.0
A new experimental determination207 by two different methods
gives for the mechanical equivalent of light a mean value of
0.00162 watt per lumen.
202 Elec. World, Jan. 2, 1915, p. 59.
203 Jour. Gas Light., Jan. 5, 1915, p. 16.
204 Elec. World, July 10, 1915, p. 71.
205 Jour. Gas Light., May 4, 1915, p. 292.
20ePhys. Rev., Mar., 1915, p. 208.
207 Phys. Rev., Apr., 1915, p. 269.
560 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
Physiology. — Further work has been done on208 the effect on
the eye of ultra-violet light. It has been shown that where the
protein in the lens of the eye has been modified by the action of
excess sugar in the body fluids, or by the action of salts of cal-
cium, magnesium, silica and the like, ultra-violet radiation may
cause cataract, but that unless this abnormal condition exists cat-
aract is not caused by this form of radiation.
Music and Color. — Several attempts to correlate music and
color have been made in the past. A Russian composer having
written a score in which was included a part to be rendered by
various colors ; a "color organ" was devised for use in a recent
presentation of the composition.209 Incandescent lamps in re-
flectors and equipped with color-filters formed the light source.
The screen was composed of strips of gauze of various weights,
mounted vertically and 8 by 10 ft. (2.43 by 3.04 m.) in size. The
lightest sheet was placed at the front, each succeeding one back
of it being heavier. The rear gauze was heavy enough to reflect
the light thrown on it. The deepest colors were thrown on the
back and the lighter colors were thrown on the front gauzes. The
color equivalents of the tone scale were as follows: C, red; D,
yellow; E, pearly blue; A, green; B-flat, steel gray; together
with intermediate values. Color organs are not new,210 several
having been constructed in recent years. The largest screen used
has been 30 by 50 ft. (9.14 by 15.24 m.).
International Commission. — At the meeting of the National Il-
lumination Committee of Great Britain held early in the year211
there was considered the question of "Rating of Light Sources
in Candlepower or Consumption," and the following resolution
was passed and transmitted to the Secretary of the International
Commission on Illumination.
It is desirable that a uniform international method be adopted for rat-
ing and marking all sources of light. It is recommended by the National
Illuminating Committee of Great Britain that the matter be considered at
the next session of the International Commission on Illumination; and
the administration of that Commission is asked to take the necessary steps
to bring this resolution to the knowledge of the different national com-
mittees, with the view to their co-operation.
2°8 Elec. World, Apr. 19. 1915, p. 912.
209 Sci. Amer. Supp., June 26, 1915, p. 408.
210 Sci. Amer., July 24, 1915, p. 79.
mjour. Gas Light., Feb. 9, 1915, p. 326.
REPORT OF THE COMMITTEE ON PROGRESS 561
LITERATURE.
The war has seriously interferred with many foreign publica-
tions having articles on illumination. The French Journal,
Science et Art de I'Eclairage, has apparently suspended publica-
tion and other French and German journals were compelled to
omit some issues, although they are now appearing regularly.
Among the books published during the year should be mentioned :
Modern Illuminants and Illuminating Engineering, by L. Gaster
and J. S. Dow. New York, The MacMillan Co., 1915.
La Lumiere Electrique et ses Differentes Applications du Theatre,
by V. Trundelle. Paris, H. Dunod and E. Pinat.
An Introduction to Color Vision, by Dr. J. H. Parsons. Cambridge
University Press, 1915.
562 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
A RESUME OF THE PHYSICAL, PHYSIOLOGICAL
AND PSYCHIC PHASES OF VISION.*
BY NELSON M. BLACK, M.D.
Synopsis: This paper is a compilation in brief of the present day
theories as to the processes involved in the visual act, considered under
the physical, physiological and psychic phases of vision.
Generally speaking the visual act may be considered as that
process whereby light, color and form are recognized by the
visual apparatus. The complex act of seeing is best studied by
dividing it into three distinct phases as suggested by Lohmann :
a physical phase concerned with the refraction and focusing
rays of light, emanating or reflected from a visible object, to
form an image on the visual surface; a physiological phase con-
sisting in the transformation of the light stimulus into a nerve
impulse. These two factors alone will not induce sight, they
must be supplemented by the third, or psychic, phase before per-
cipient vision results.
PHYSICAL PHASES.
The visual apparatus consists of three essential parts: (1) the
eyeball with its contents; (2) the optic nerve, and (3) the visual
centers of the brain.
The eyeball may be compared with a camera in that it con-
tains a diaphragm shutter and a lens, or, focusing system, and
has to do with the physical phase of vision. The optic nerve
terminals act as the sensitized background of the camera and the
nerve fibers conduct the excitations produced during the
physiological phase to the various centers in the brain which
have to do with the psychic phase in the recognition of light,
color and form.
The structures of the eyeball concerned in the physical phase
are the cornea (Fig. 1) which is situated at the anterior pole of
the eyeball and differs from the dense, pearly white, semi-opaque
protective scleral coat of which it is a part, in that it has been
specialized to admit light into the interior of the eye. It is very
* The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
black: phases of vision 563
transparent and has a refractive index (1.337) slightly higher
than that of water. Its two surfaces being so nearly parallel,
the course of light rays is not appreciably altered in passing
through it.
Back of the cornea, in an especially prepared chamber filled
with a fluid of about the consistency of water, in which it can
operate with greatest ease, is the diaphragm shutter or iris.
This important part of the visual apparatus is a specialized por-
tion of the middle, or, choroid coat, which furnishes nourish-
ment to the other structures of the eye as it carries the blood
Fig. 1. — Schematic cross section of eyeball.
vessels. This coat also is deeply pigmented and shuts out ex-
traneous light. The iris, which is opaque owing to the deposits
of pigments of different color in its substance, contains circular
muscular fibers for making the pupil smaller and radiating fibers
which act in opposition. The inner or pupillary edge of the iris
is separated from the lens or focusing system by a thin layer of
fluid known as the aqueous humor.
The lens is an elastic crystalline body held in suspension be-
tween two layers of thin transparent membrane, the lens capsule,
which meet at the periphery of the lens and is attached to an-
other specialized portion of the choroid coat, called the ciliary
body which regulates the focusing power of the lens by con-
trolling its polar diameter, a process known as accommodation.
564 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
When the ciliary muscle is in a state of rest, the tension of the
suspensory ligament acting on the lens flattens it to such an extent, that
provided the refraction of the eye be normal, parallel rays of light fall-
ing on the cornea are brought to a focus on the retina. Rays from any
nearer point are divergent when they strike the cornea, and the refrac-
tive power of the lens at rest is only sufficient to focus them at a point
behind the retina. When, however, the circular muscle contracts, the
suspensory ligament relaxes, and the lens, by virtue of the elasticity of
its capsule, changes its shape and thereby increases its refractive power.
The result of this is that the divergent rays of light can now be brought
to a focus upon the retina. (Lohmann.)
The lens fits into a saucer-like depression of the vitreous body.
This is a clear jelly like substance having a refractive index
(1.3365) nearly the same as water, surrounded by a very delicate
perfectly transparent capsule, the hyaloid membrane. The
function of the vitreous body, which occupies about two thirds
Fig. 2. — Changes in the lens during accommodation.
of the contents of the eyeball, is of considerable importance as it
helps maintain the shape of the globe and holds the lens firmly
in position.
Surrounding about four fifths of the vitreous body is the
retina or what is commonly called the inner or third coat of the
eye. In reality this so called coat is an outgrowth of the brain
and consists of a spreading out of the fibers of the optic nerve
over the entire back four fifths of the eye. By process of evolu-
tion this tissue has become a highly specialized nervous structure
possessing the power of transforming impinging rediations of
known wave-length into nerve stimuli. These excitations are
transmitted by the fibers of the optic nerves, which each contain
approximately 1,000,000 fibers, to the visual centers of the brain.
The retina or eye ground is the receptive layer of the visual
black: phases of vision
565
apparatus corresponding to the sensitized plate of the camera
upon which the images of external objects are constantly being
formed.
The fibers of the optic nerve upon reaching the interior of the
eye spread out in all directions and then turn back in the direction
they entered, Fig. 3. Each individual fiber is connected with a cell
called a ganglion cell, c, Fig. 3. From these ganglion cells other
fibers pass outward to so-called bipolar cells, the outer poles of
which end in many branches or arborisations, Fig. 3, as they are
Fig. 3. — Schematic representation of distribution of nerve
connections in retina.
called, which connect with the branches of other bipolar cells, b,
Fig. 3. From these arborizations fibers extend vertically outward
which end in a series of peculiar bodies called the rods and cones,
a, b, Fig. 4. These are the terminals of the optic nerve fibers, and
seen from above form a mosaic pattern, composed of about 5,000,-
000 minute disks, which differs in various portions of the retina.
It is particularly noticeable that 2 to 10 or even more rods are em-
braced by a single arborization which represents one fiber of the
optic nerve, Fig. 4. On the other hand each cone has a nerve fiber
belonging exclusively to it. This will be referred to later on. At
or near the periphery of the retina the cones are few in number
and the mosaic pattern is made up of a larger disk surrounded
566 TRANSACTIONS OE IEEUMINATING ENGINEERING SOCIETY
by many rows of smaller disks; as we near that portion of the
retina corresponding to the visual axis of the eye the cones be-
come more numerous and the rod less until only cones are found.
The ends of the rods are in contact with six sided cells called
pigment cells which are filled with fine granules and have a net
wrork of fine spindle shaped bodies which push forward under
the action of light between the ends of the rods as far as the
cones. The spaces between the rods and cones and pigment cells
Fig. 4.— Schematic representation of rods and cones.
is filled with a fluid which contains a photochemical substance
very sensitive to the action of light known as the visual purple.
In line with the visual axis at the posterior pole of the eye is
situated an area of the retina in which vision is most distinct
called the macula. This area is about 2-2.5 mm- in diam-
eter. Here the rods are found in much less number until in
a small pit at the center of the macular called the fovea only
cones are present. The cones in the fovea differ from those
found in other parts of the retina in that they are long, very
black: phases of vision
567
narrow cylinders closely massed together apparently to get as
many as possible in a small space. Thus an image projected
upon the fovea will cover many more cones than upon other areas
of the fundus, Fig. 5. Microscopical measurements of the thick-
ness of the cones in the foveal region finds they vary from 0.0015
mm. to 0.0054 mm. in diameter. The ability to distinguish two
points depend upon the diameter of the cones in the center of
exact vision. To be able to perceive two points as distinct and
separate they must fall upon cones which are separated by at
least one resting cone.
Fig. 5. — The fundus or background of the eye.
Distinct vision is found only in the macular area, a rounded
patch about 2 mm. across which subtends in the human eye an
angle of about 5 minutes in the field of vision which is the visual
angle of the macula. Critical vision is to be found only in the
fovea which occupies an angle in the field of vision of less than
1 minute which is the visual angle of the fovea. In a schematic
eye calculated by Listing a visual angle of 1 minute corresponds
on the retina to a distance of 0.00438 mm. or about the average
diameter of a cone.
Outside of the macular region we obtain a general impression
568 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
of the form and color of objects over the whole of the retinal field
and as a matter of fact in reading ordinary print we only see
words of about four letters at a time and it is by rapid movements
of the eye in various directions that gives the idea of seeing con-
tinuously.
This brings us to the muscles which control the movements of
the eyeballs and by which the visual axes may be directed to any
point in the field of regard. These are six in number for each
eye and by reason of their attachment on the eyeball turn it up,
down, in, out and if working in conjunction with each other
orient the eye in any of the intermediate positions, Fig. 6.
Fig. 6. — Bxtrinsic muscles of eye.
The discussion so far has shown that we have in the normal
eye an apparatus which allows the entrance of impinging rays of
light, extraneous rays are largely cut out by a diaphragm, which
acts reflexly depending upon the intensity of the light; a lens
brings the rays of light to a focus up a highly organized nervous
structure thus completing the physical phase of the visual act.
PHYSIOLOGICAL PHASE.
The highly organized nervous structure or retina transforms
the radiant energy waves into nerve stimuli constituting the
physiological phase.
black: phases of vision
569
The fibers of the optic nerve are as insensible to light as the
fibers of other nerve trunks, as is demonstrated by the experi-
ment first performed by Mariotte who discovered the blind spot
in the eye. Purkinje demonstrated that the light perceiving
portion of the eye must lie behind the nerve fiber layer of the
retina from the fact that we can perceive the shadow of the re-
tinal vessels in our own eyes. Exact physiological measurements
Fig. 7.— Microphotograph of cross section of retina, showing (a) pigment
cell layer, (b) rod and cone layer.
has shown that the distance between the vessels and the light per-
ceiving layer must be from 0.17 to 0.33 mm. which distance takes
us to the rod and cone layer. Hence it follows with great prob-
ability that the latter structures, the rods and cones, are the light
perceiving parts of the retina.
This in fact is substantiated by the anatomical relations of the
rods and cones to the individual nerve fibers of the optic nerve.
The excitation which will effect the receptive portion of the
specialized organs of sense differ materially from those capable of
570 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
stimulating the nerve fibers themselves and must be converted by
the terminal organ into the adequate kind of nerve excitant.
Nervous stimuli are of mechanical, electrical, thermal or chem-
ical nature and into such character must external energy be
transformed when it varies from the nervous stimuli in quantity
or when it is of a different quality, such e. g., as waves of sound
or light.
Retinal Changes Due to Light. — When light falls upon freshly
exposed retina the latter undergoes a number of changes which
are objectively demonstrable. The spindle shaped pigment gran-
ules in the pigment layer migrate toward the rod and cone layer.
The pigment will not move if the central nervous system is de-
stroyed, and its reaction may take place in one eye as a conse-
a
—
A B
Fig. 8.— Section through the retina of a frog's eye, after Engelmannn. A, after the eye
was kept for from one to two days in complete darkness ; B, kept for 24 hours in the
dark, then exposed for one-half hour to diffused bright daylight.
quence of light falling on the opposite retina. The cones which
in darkness or dim light are near the pigment layer move inward
toward the nerve fiber layer. The rods on the other hand elon-
gate under the influence of light, their movement being opposite
to the cones. The galvanometer shows the action current of the
retina directed from the nerve fiber layer to the rod and cone
layer undergoes a positive variation which changes upon the
removal of the light stimulus.
After the eye has been kept in darkness for a time there is a
marked difference in the sensitiveness of the retina to light.
13LACK: PHASES OF VISION
571
This is known as dark adaptation, Fig. 9. In this state the periph-
eral regions of the retina are relatively more sensitive than the
fovea to light of moderate intensity and to short wave-length.
Adaptation to darkness is characterized by an increase in respon-
siveness to short waved light, and this change is mainly if not en-
tirely, extra foveal. The perception of colored light varies in
different portions of the retina, being sharpest at the fovea.
Passing toward the periphery the color sense gradually
diminishes. For the colors yellow, blue, red and green, yellow
has the most extensive field, blue next and green the least. Most
ISO
160
170
I6C
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0,
VISUAL ACUITY FOR
LIGHT ADAPTATION
• DARK ADAPTATION
60- 50 40 30 23 10 0° 10 20 30 40 50 60 70'
Fig. 9.— Visual acuity curves for light and dark adaptation.
authors state the extreme periphery of the retina is totally color
blind.
The visual purple which is present in all parts of the retina
except the fovea or yellow spot (note the exception) and is
found mainly in the outer limbs of the rods fades or is decom-
posed when exposed to light.
The bleaching or decomposition of the visual purple depends
on the intensity of the light, and while all colored light has the
power of decomposing this substance, with weaker light, hours
and even days, are needed to complete the action. With dif-
ferent colors of monochromatic light the process takes more or
less time; "in yellow green the purple is altered instantaneously;
572 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
in the spectral colors, from greenish yellow to indigo, the process
requires from 2 to 10 minutes; in yellow, 20 minutes; in violet
and orange, 30 minutes; in ultra-violet, 45 minutes, and in red
still a somewhat longer period of time." While blended light,
including waves of greater and lesser refrangibility produces the
BLUE
&REEN
Fig. 10. — Chart for recording boundaries of color field. Chart on right shows
boundaries of normal color field by Wm. Mcl,ean.
^0
270°
Fig. 11. — Binocular field of vision.
Fig. 12. — Binocular field of view.
maximum effect, each individual color of such mixture acts for
itself, and only better so far as the total decomposition of the
purple is concerned, when it is united with the others. The
electrical response of the retina appears in the apparent absence
of the visual purple, although the reaction is more intense if this
black: phases of vision 573
pigment be present, and it is clear that the whole effect varies in
intensity with the part of the spectrum employed. Regenera-
tion of the visual purple in the outer segments of the rods takes
place rapidly in darkness or dim light, apparently being derived
from a substance contained in the pigment cells known as
rhodophyllia.
Visual Acuity. — The sensitivity curve of the eye for lumin-
osity at ordinary intensities shows a maximum effect in the yel-
low and green portion of the spectrum. Dr. Louis Bell states that
it is only by virtue of the high maximum point in the luminosity
curve of the eye that we are able to see distinctly at all, and
that if the extremes of the spectrum were highly luminous there
would be no definite focal surface for which accommodation
could be adjusted, the violet rays being brought to a focus in
front of the retina and the red rays behind it in the emmetropic
eye. It is a well known fact that the luminosity curve of the
eye varies with the intensity of the light, shifting toward the
green with illumination of low intensity and toward the orange
and red with illumination of high intensity.
Luckiesh has determined that visual acuity, for a reading dis-
tance of 2>Z cm. with monochromatic light, is greatest in the yel-
low green of the spectrum. Thus, it would seem that the radiant
energy which has the greatest decomposing action on the visual
substance is productive of the greatest visual efficiency, that is.
the yellow green waves.
Duplicity Theory of the Function of the Retinal Structures. —
The reaction of the different areas of the retina to light stimuli
in the conditions known as light and dark adaptation studied in
conjunction with the difference in the histological structures be-
tween the fovea and the surrounding retinal area has given rise
to a theory of the function of the rods and cones, i. e., two dis-
tinct mechanisms exist. The cones are concerned only with the
recognition of colors and of colorless sensations, can only act in
bright light and their responsiveness is little if at all increased by
resting in darkness. The rods are unaffected by colored light
but are brought into play when the eye has been shielded from
light, and, are the chief factors in twilight vision.
Duplicity Theory. — This theory does not account for the
574 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
activity of the cones in the peripheral portions of the retina which
are not by any means functionless in either light or dark adapta-
tion.
The difference between acute central vision and indistinct
peripheral vision is marked and while central vision is far
superior to peripheral in respect to the optical perfection of the
image of an object and the fine perception of detail, peripheral
vision is superior in the perception of movement.
Corresponding to these functional differences the eye may be
considered as an organ which unites two forms of apparatus of
different functional value.
The "central eye" is an elongated eye with a narrow-angle
field ; the possibility of a high grade of visual acuity is associated
with the delicately inlaid sensory elements, and the provision of
an isolated sensory path for each end element. The "peripheral
eye," on the other hand, has a wide angle field and a mosaic of
end elements with concentrated sensory connections, and is less
adapted for keen perception of detail. The periphery, however,
has an advantage over the center in the elements necessary for
vision in dim light. This great difference in the conditions of
acuity in the center and in the periphery of the retina is evidently
connected with some anatomical peculiarity of the area in the cen-
ter, and this, as has already been mentioned, is found in the iso-
lated individual nerve connections of this part in contrast to the
more concentrated ones in the periphery. The areas of discrete
sensation in the retina, therefore, differ according to their posi-
tion, and in the elaboration of this idea the gradual diminution
in number of the cones from the center to the periphery is sig-
nificant. In the center of the retina cones alone occur, but as
we pass outwards rows of one, two, three or four rods are in-
terposed between the cones which themselves become thicker.
The correspondence appears a simple one, but a more careful
comparison will show that the diminution in acuity is propor-
tionately greater than the reduction in the cones.
In support of the duplicity theory various facts of physiological
optics are given:
The Colorless Interval. — If a feeble spectrum be observed by
BLACK : PHASES OF VISION 575
an eye well adapted for darkness, colorless light will first be seen,
and only as the intensity is increased will color be perceived.
Purkinje's Phenomenon. — If selected matched red and blue
objects are placed together so that in daylight the red appears
lighter than the blue, and the illumination be gradually reduced,
as adaptation increases and the illumination diminishes, the red
object will grow darker and even appear black, while, on the
contrary, the blue will grow lighter and more white.
The variation of the maximum point of the luminosity curve
for different intensities of light was mentioned above, for the dark
adapted eye the maximum point is found to be in the green.
(533 /*/*•) Investigations have shown a correspondence between
the curve of scotopic or dark luminosity and that obtained by the
bleaching effect of light upon the visual purple. This corres-
pondence in the curves can not be accidental and the upholders
of the duplicity theory see in the visual purple and the structures
which contain it, the rods, the elements and the visual material
for vision in the dusk. The view of the duplicity theory that the
sensation of white (and grey) in the light adapted eye is brought
about by the color-perceiving cone elements, and in the dark
adapted eye by the rods and the visual purple, is freely consid-
ered to be very doubtful. It must not be forgotten that the facts
given above have hardly any analogy in the physiology of the
other senses. The supporters of the duplicity theory consider
total color-blindness as a condition of the eye in which sensation
occurs entirely through the activity of the retinal rods, which con-
tain the visual purple; the cones being absent or functionless.
The peculiar distribution of luminosity in the spectrum of the
totally color-blind appears to favor this view, the complete ab-
sence of color vision and the photophobia also agree with it.
The functional activity of the rods alone is favored by the con-
dition of visual acuity, which differs from that of color seeing
people, in that it increases in a different manner when the light
is increased, and does not show that sharp bend upwards, which
in the normal can be referred to the visual power of the cones.
In the totally color blind the existence of a central scotoma for
color such as is found in the dark adapted eye with feeble light
would be especially significant, for, a defect must be present at
576 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
the point of central vision to correspond with the dark adapted
eye. In many cases, though not in all, such scotoma can be
found.
The idea that the cones have a lower sensibility in total color-
blindness is a very attractive one as their complete absence does
not appear proven by the observations which we have been con-
sidering. The defective vision, the absence of color sensation,
and the other symptoms can be considered, without any straining,
as due to a severe restriction of the function of the cones along
with an increase in that of the rods.
Mechanical Theory of Vision. — It has been assumed by some
observers that the light waves act mechanically, the wave move-
ments setting into vibration portions of the external segments of
the rods and cones, and that this mechanical movement forms
the direct excitant of the nerve impulses. The general view at
the present time, however, is that the process is photochemical ;
that is, the impact of the ether waves sets up chemical changes
in the rods or cones which in turn gives rise to nerve impulses
that are transmitted to the brain.
Color Vision. — This brings us to the physiology of the percep-
tion of colored light and the theories advanced to account for the
peculiar condition of vision found in about one out of every
twenty-five males known as color-blindness. There are many
theories advanced, the chief among which are those of Young-
Helmholtz, Hering, and Edridge-Green.
The Young-Helmholtz Theory. — This theory (first proposed by-
Thomas Young in 1807, and subsequently modified by Helmholtz) assumes
that the terminal fibrils of the retina are arranged in three distinct sets
for the reception of the three primary colors — red, green, and violet.
These groups correspond to the three colors, and acting simultaneously
induce the sensation of white. Red light entering the eye affects to the
greatest extent the group of filaments known as the red sensitive elements,
and also affects the others to a slight degree. In like manner green and
violet are perceived by their corresponding sensitive elements. The
absence or imperfect development of the retinal area set aside for one
of these primary colors will cause this color to be seen as if composed of
the two remaining colors, thus giving rise to color blindness corresponding
to the deficient color elements.
black: phases of vision
577
Fig. 13 shows the manner in which the quantitative stimula-
tion of the individual fibers by yellow or blue is to be appreciated
on this hypothesis.
The conclusions drawn from the laws of light mixture have
in recent times found a technical application of this theory in
the Lumiere color photography. In front of a sensitive plate
is a screen formed of minute grains of starch colored red,
green and violet. The variously colored light passes through
the starch grains in a selective manner with respect to quantity
and quality, according to the valency curves and makes its
impression on the bromo silver plate. The plate is then de-
veloped as a diapositive, and will filter light in the same manner,
RtO 0RAN6E YELLOW
Fig. 13. — Valency curves of the three components of the color sense.
only allowing the original colors to pass ; thus a very fine photo-
graph in natural colors can be obtained.
Hering Theory of Color Vision. — This theory assumes the existence
of three separate visual substances in the retina. Each of these substances
is decomposed by the action of light and is renewed when the eye is per-
mitted to rest in the dark. Both the decomposition and the renewal of
the visual substances result in the production of color sensation.
The Hering visual substances are divided into three sets of two each,
i.e., (1) white-black substance; (2) red-green substance; (3) blue-yellow
substance.
When the black-white substance is decomposed the sensation of white
is produced. When this substance is renewed the sensation of darkness
results.
When the red-green substance is decomposed the sensation of red is
produced, and when it is renewed the sensation of green results.
When the yellow-blue substance is decomposed the sensation of yellow
is produced; when it is renewed the sensation of blue results.
Red light produces the sensation of red by decomposing the red-green
substance. Orange light produces the sensation of orange by decom-
posing both the red-green and the yellow-blue substances. Yellow light
produces a sensation of yellow by decomposing the yellow-blue substance,
the red-green being then in equilibrium. Green light produces the sensa-
5
578 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
tion of green by the renewal of the red-green substance, the yellow-blue
being now in equilibrium. Blue light produces the sensation of blue
by the renewal of the yellow-blue substance. Violet light does the same,
though to a less degree.
This objection can be taken to Hering's theory, that in the
black-white form of sensation there is no different point which
cannot be compared to white or to black, as is the case with the
red-green or the blue-yellow; there is also a doubtful element in
the hypothesis in that it is not only the process of dissimilation
that produces a stimulus, but perception may also be due to
assimilation. The well known phenomena of contrasts are well
explained by this hypothesis ; i. e., after steadily fixing a colored
pigment, and then looking at a colorless surface, the contrast
color appears. Just as this "successive contrast" is well explained,
so also is the "simultaneous contrast." In this condition, which
is shown in the appearance of colored fringes, the dissimilation
of a definite visual substance will induce the assimilation of the
same substance in the adjoining parts, and thus the appearance
of the complimentary color. Color perception in peripheral vision
is also in favor of Hering's theory.
The Edridge-Green Theory. — The latest and probably most
comprehensive theory is that of Edridge-Green in which he
accounts not only for vision and color vision, but for the trans-
formation of radiant energy into nerve stimuli.
Edridge-Green conceives that the cones are the terminal per-
ceptive visual organs. The rods are not perceptive elements, but
are concerned with the formation and distribution of the visual
purple. Vision takes place by stimulation of the cones through
the photo-chemical decomposition by light of the liquid surround-
ing them which is sensitized by the visual purple.
The character of the stimulus differs according to the wave-
length of the light causing it. In the excitation itself we have the
physiological basis of the sensation of light, and in the quality
or wave-length of the excitation the physiological basis for the
sensation of color.
There are three objections made to the Edridge-Green theory
that the visual purple is the visual substance.
(i) The chief objection is that it is not present in the cones.
The author maintains this is a necessary requisite to the theory.
black: phases of vision 579
(2) That animals such as frogs naturally possessing the pig-
ment continue to see after their visual purple has been absolutely
bleached by prolonged exposure to strong light. The author
contends that the retinas which were bleached by sunlight and
with which the frogs were still able to see, in reality contain
sufficient visual purple or its decomposition products for vision,
but not enough for external recognition.
(3) That the visual purple is entirely wanting in some animals
which see very well. This is based upon erroneous observations,
and in case of certain animals supposed to have no visual purple
or no rods, subsequent observers have found both ; for instance,
the butterfly, bat and tortoise. Even if there were no visual
purple the argument fails because there might be some other
means of stimulating the cones.
The following are a number of arguments given in support of
the Edridge-Green theory :
( 1 ) Visual Acuity : This corresponds roughly to the distribu-
tion of the cones. Though the rods are much more numerous in
the periphery of the retina visual acuity is very much less with
this part.
(2) The relation between the foveal and the para-foveal
regions. As there are no rods in the fovea, if the rods and cones
were percipient elements of a different character there ought to
be a qualitative difference between these regions. The Purkinje
phenomenon, i. e., the alteration of optical white equations by the
state of dark adaptation, the colorless interval for spectral lights
of increasing intensity, the different phases of the after-image,
all exist, not only in the para-foveal, but also, only gradually
diminished, in the foveal region.
The misstatement has been made that the Purkinje phenomenon
(the fact that if an equally bright red and blue be viewed by a
light of considerably diminished intensity the blue appears much
brighter than the red) is not found in the foveal region. One can
easily ascertain for himself that the Purkinje phenomenon is
found in the fovea by taking a red and a blue into a dimly-lighted
room, the red being brighter than the blue in ordinary conditions,
he will find that the blue will appear brighter than the red with
direct vision, and still more so with indirect vision, he will find
580 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
that in no position of the eye can he see the red brighter than the
blue.
(3) Chemical Analogy: The visual purple gives a curve which
is similar to that of many other photo-chemical substances. With
such substances a different curve is obtained with weak light from
that observed with light of greater intensity and it is reasonable
to suppose that the visual purple which is formed by the pigment
cells under the influence of a bright light would be somewhat dif-
ferent in character from that which is formed in darkness.
(4) It is a misstatement that the periphery of the retina is
color-blind. It is entirely a matter of the intensity of the light
employed. Bright spectral colors can be seen at the extreme
periphery of vision. All lights when sufficiently small and feeble
appear white even at the fovea.
(5) The varying sensibility of the fovea is explained on the
theory that when there is visual purple in the fovea this is the
most sensitive portion of the retina; when there is none there it
is blind. It also shows conclusively that the fovea is sensitized
from the periphery.
(6) Disappearance of lights falling upon the fovea shows that
when the visual purple in this area is used up and not renewed
the latter is blind.
(7) Currents seen in the field of vision are not due to the cir-
culation but are formed by the flow of sensitized liquid.
(8) The movement of positive after images by a jerk of the
head shows that the photo-chemical stimulus is external to the
cones and can be moved.
(9) Dark adaptation is easily explained by assuming that the
liquid round the cones becomes more sensitive through a greater
percentage of visual purple being poured into it. In light adapta-
tion the anatomical arrangement is such as to prevent as far as
possible the decomposition of the visual purple.
The ability of the normal eye to distinguish the form of an
object depends upon (1) the size of the image received upon the
retina; (2) the amount of light reflected from it; (3) the con-
trast with the background. The results obtained from the exam-
ination of a great many individuals with good sight have shown
that with the average eye the form of an object can be recog-
black: phases of vision 581
nized if the angle subtended by it at the retina equals five min-
utes and parts of the object, such as a letter, which subtend a
5-minute angle, are wide enough to subtend a 1 -minute angle.
The amount of light reflected from an object must be suf-
ficient to act upon the photo-chemical visual substance and cause
stimulation of the nerve endings. The coefficient of reflection
between an object viewed and the background must differ suf-
ficiently to make a contrast; otherwise the object will be in-
visible.
Summary of Physiological Phases of Vision. — A light wave
starts on its journey through the ether from some luminous ob-
ject or reflected from some surface which is its source. The
various rays parallel, divergent or convergent, as the case may
be, are brought to a focus upon the background of the eye. The
first step towards its becoming a visual impulse is taken when it
decomposes the photo-chemical substance of the retina, thus
setting up vibrations in the cones of this membrane.
The excitation received by the retinal substance and
structures is conveyed by fibers of the optic nerve back to centers
at the base of the brain, and either directly or by new relays of
fibers to the visual centers of the brain. Definite portions of the
retina are related to equally definite portions of the visual center
of the brain which first receive the projected retinal excitations.
The result in the brain centers first receiving the impulses is a
visual sensation or percept. Up to this time, however, no idea
of the object looked at is obtained. In order that this shall come
to pass the brain excitation which has been brought about must
be transmitted to another region of the brain surface; in other
words, from a simple perception center to a memory center
where it is recognized.
There are several factors which interfere with the adequate
carrying out of the physical phase of vision, such as far-sighted-
ness, near-sightedness and astigmatism. However, as we are
considering a normal or emmetropic eye, this will not be gone
into.
The sensitiveness of the visual apparatus to radiant energy is
a most interesting and absorbing study, but time and space will
not allow of more than a mere mention.
582 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Of all the energy emanating from a light source, such as an
incandescent lamp, only 5 per cent, is perceived by the eye as
light, as is graphically represented by slide projected on the
screen. This small portion of the radiant energy of an incan-
descent body appreciated by the eye is known as the visible spec-
trum, and is bounded by wave-lengths 760 fx/x, recognized as
deepest red, and wave-length about 400 /*/*, seen as deepest violet.
The action upon the eye of wave-lengths longer than 760 pn,
known as infra-red rays, is still, to a certain extent, a moot
question, but they are considered to be a factor in producing
opacities of the lens. The wave-lengths shorter than 400 fifx are
designated as ultra-violet rays, and are known to produce intense
inflammatory reactions of the outer coats of an unprotected eye,
when exposed to intense light, containing a high percentage of
these radiations.
The various transparent media of the eye, the cornea, aqueous
humor, lens and vitreous, have selective absorption characteris-
tics for these rays, which protect the retina under ordinary con-
ditions. As infra-red and ultra-violet radiations are of no known
aid in the visual act, it is a wise precaution to shield the eyes
from them by means of protective glasses, which have selective
absorption action for these particular rays, provided, however,
that the glass does not cut down the amount of light gaining
entrance into the eye to an extent that will interfere with the
proper decomposition of the visual purple. The selective absorp-
tion of some of these glasses is shown.
The subject of after images, color contrasts, simultaneous con-
trasts, complementary colors, recurrent vision, binocular vision
and spatial vision, cannot be gone into in the time and space
allotted.
PSYCHICAL PHASE.
The psychical phase of vision will be briefly mentioned, and is
largely quoted from Lohmann :
While color perception by the eye is induced from a light stim-
ulus and the essential conditions are generally provided by physio-
logical stimuli, the perception of color itself is a psychic phe-
nomenon. With the color impression called forth by the stimulus
are associated those representations called memory-colors, and
black: phases of vision 583
thus the same percept is insured even though surrounding con-
ditions vary. Cloths, whose color has been recognized by day,
are viewed by artificial light, when to a really unprejudiced eye,
they present quite another appearance, but seem to be seen in
their "correct" colors in the artificial light ; we also speak of
white snow, even when the dusk of twilight has changed it to
grey.
The psychic element in vision is very obvious in the following
example, which Helmholtz gives in his "Physiological Optics."
Imagine oneself to be in a brightly lighted room; impressions are
then accompanied by powerful sensations. We find ourselves
at dusk in the same room, seeing only the lighter objects, and
these indistinctly. Everything which we notice so fuses with
our memory-pictures that we can readily find objects looked for.
Even in absolute darkness, we can find our way in the room by
virtue of the memory of previous visual impressions. This
example of the reduction of the presentation image "by an ever
increasing elimination of its sense elements to a pure re-presenta-
tion image," shows us the intimate connection between the purely
sensory and the purely psychic in our concepts and ideas.
In fact, our concepts are not induced merely by the visual im-
pressions of the moment, but necessitate the addition to these of
re-presentations of sensations; these we adequately term
"factors of experience." It is not always possible to separate the
pure sensation from the factor of experience.
When I look at a portrait drawn so that the eyes look at me,
and then walk about the room, I have the impression that the
portrait is always gazing at me. This fixed gaze of the portrait,
an easily proved empiricism, is not induced by reflexion, but is
the result of an overwhelming sensory impression.
The analysis of the fact that the factor of experience is so
important in vision, is by no means simple; it presents a difficult
problem to the psychologist. A relatively simple explanation is
provided by the hypothesis that the psycho-physical substance
as a result of its activity suffers changes, and that residual sen-
sations previously left behind are met with and have a modifying
action on a new sense impression.
To produce a picture from the individual sensory stimuli of
584 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
the retina, we must have the component parts built up into a
complex percept. Witasek talks of a "process of production,"
and his meaning becomes clear when we consider how the same
form of stimulus in the same state of the eye can produce dif-
ferent perceptions.
Importance of Vision. — In examining the importance of vision,
we must take into account the relation of our eye to objects seen,
and also the relation of the objects to us. We have to answer
two questions: 1. What does sight convey to us regarding ex-
ternal objects? 2. What influence has sight on our intellectual
life and comfort?
What Does Sight Convey to Us? — The first question intro-
duces a much discussed philosophical problem, and ends in the
well known question of objective existence. We either deny a
correspondence between our perceptions and the actual objects,
and explain all sense perceptions as subjctive phenomena, and
sense delusions as not actual realities ; or we admit a conformity
between the world around us as we subjectively find it, and as it
objectively exists.
In the latter case we speak of a "pre-established harmony"
(Ehrhart), and consider that a correlation between mind and
matter is shown because the power of mind is derived from the
same source as are the forms of energy in the world around.
In contrast to such speculative answers to the problem of the
relation between vision and the world around, Helmholtz em-
phasized the practical point, which appears when we consider
that surrounding objects by means of our sense impressions be-
come to us symbols which, when we have learnt to interpret
rightly, make it possible for us to direct our actions so as to
bring about desired results. Although the eye is extremely use-
ful, practically, it cannot see at all distances, nor perceive all the
vibrations of the ether. In the same way we have no guarantee
that human intelligence might master everything which can exist
or occur.
The common view of simple people that our vision says some-
thing about an object has led to an unfortunate method of ex-
pression, which appears when we speak of "red" sealing wax.
black: phases of vision 585
To a color-blind eye, this is not red; it is only in the case of a
normal eye under ordinary conditions that the rays of light re-
flected from the sealing wax produce that definitely character-
ized sensation (red).
Influence of Sight on Intellect. — Regarding the second ques-
tion, the importance of vision to our intellectual life, the view was
prevalent amongst the ancients that the many distractions which
our visual impressions bring us, prevented an undisturbed devel-
opment of the soul. Cicero's statement that Democritus had
blinded himself in order to reason more clearly would thus be
easily understood. We tend, when reasoning, to shut our eyes;
but their closing is only temporary against any influence which
would interfere with the concentration of the mind. On the other
hand, we must recognize that the "hasty glance" will, through
visual impressions advance our quickness of mind, and to a cer-
tain extent is a form of mental gymnastics.
The eye is an organ which enables us not only to recognize
objects in the vicinity, but also parts of the country, the sea, and
the starry sky, in the far distance. Our visual impressions are
closely related to perceptions of space, and recognition of time.
We will readily be convinced that a spatial sensation of depth is
transmitted (extent in height and breadth is conveyed by each
eye separately) if we attempt to estimate the position of an ob-
ject relative to ourselves by monocular vision. It must be ad-
mitted that depth is only recognized indirectly with the one eye,
in contrast to the immediate and obvious estimation of the posi-
tion of objects one behind the other which is gained binocularly.
Impressions as to succession in time are also conveyed by our
visual sense; and it might be added, more frequently by this
means than by the other sense organs. For the whole field of
vision forms the fundamental chord, the continuous impression,
in which a movement or an alteration occurs; we see solid ob-
jects grouped together constantly, changing in their relative
positions. It is thus quite obvious what a great intellectual use
we make of our visual impressions, so variable in space and time.
The whole play of our imagination draws freely for material
on memory pictures derived from vision, so that visual impres-
sions are the source of a large portion of our inner life.
586 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
The true importance of vision to us will be clear if we try to
imagine what would remain of our intellectual existence if all
visual impressions and the memory of them, were banished. We
must confess with Goethe:
"Place yourself in what state you will, you will always think
of yourself as seeing."
ILLUMINATION CALCULATIONS 587
SIMPLIFICATION OF ILLUMINATION
CALCULATIONS.*
BY A. S. MCALLISTER.
As marking the transition of the science and art of illumination
from the methods of the physicist to those of the engineer, no
one milestone stands out more prominently than that represented
by the presidential address of Dr. Clayton H. Sharp in 1907.
Following his presentation of certain concepts and terminology
in illuminating engineering, not only was there a change in the
output rating of lamps from the indefinite and much abused
candlepower to the definite and now well-understood lumen, but
many improved methods were developed for solving problems in
illumination. In many respects the results have been similar to
the substitution of the flux method for the isolated unit pole
method of solving problems in magnetism.
While from the point of view of physics there are marked
differences between the concept of magnetic lines or "tubes" force
and that of lines or "cones" of radiant energy, yet in their math-
ematical treatment the problems relating to the one are quite
similar to those relating to the other.
So far as numerical results are concerned, it is absolutely safe
to ignore the direction of travel and mode of propagation of the
radiant energy from the source of light to the surfaces upon which
this energy is absorbed. Of one relation we can be absolutely
sure, namely, the total energy absorbed equals the total energy-
produced. When methods of calculation give results not in con-
formity with this relation it is safe to state that the methods are
wrong either in principle or in application. Thus for checking
results obtained by more laborious methods the absorption-of-light
method is highly advantageous. In many instances, yes in most
cases, it is permissible to abandon the more complicated methods
and rely upon the simplest and absolutely correct energy-ratio
method, with merely an occasional reference to some more in-
direct method for determining the space distribution of the
illumination where this is of importance.
* Presidential address at ninth annual convention of the Illuminating Engineering
Society, Washington D. C, Sept. 20-23, I9I5-
588 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Looking back over the Transactions of the Illuminating En-
gineering Society since its first meeting in 1906, one cannot but
be impressed by the fact that almost all of the solutions offered
for problems in illumination have been based on the tacit assump-
tion of point sources rather than surface sources. Even when
dealing with plane surface sources the authors have usually
treated them as made up of an infinite number of point sources
arranged in one plane, and have based their solutions on the "in-
verse square" law and other relations developed from the funda-
mental point-source conception. In order to obtain results con-
sistent with the known facts in this case, it has been necessary to
assign to each infinitesimal point source in the plane certain
physical characteristics not possessed by ideal point sources, such
as the ability to produce light in only one hemisphere which is the
fundamental attribute of an infinitesimal plane surface source.
It needs no argument to show that all calculations are im-
mensely simplified by adopting initially the surface source con-
ception and utilizing at once the well-known relations developed
for surface sources.
Instead of determining the illumination produced by the source
on a chosen plane by reference to the "inverse square" law and
the integrated "candlepower," the identical value can be derived
more conveniently by means of the fundamental ratio existing
between the "apparent luminous density" of the source and the
lumen density on the surface illuminated, which ratio depends
solely upon the solid angle subtended by the source when viewed
from the chosen plane.
Allow me to call attention at this point to a fact learned by
us all in our school days, but mostly forgotten since then ; namely,
the extreme ease with which solid angular relations can be rep-
resented by straight lines and circles in planes. As a result of
this fact simple circle diagrams can be utilized for solving graph-
ically problems in solid angular relations the solutions of which
become very complicated when any other method is employed.
Ignoring for the moment the physical interpretation of the
change in conception from the "point" to the "surface" source
allow me to mention here the significant fact that the solution of
a problem when based on the one conception is identical with that
ILLUMINATION CALCULATIONS 589
found when the other conception is employed, so that any errors
which may be attributed to the one conception must likewise be
urged against the other.
When dealing with surface sources it is necessary to take into
consideration the fact that not all surfaces obey the so-called
"cosine law" of emission in accordance with which a surface
would appear uniformly bright when viewed from all possible
locations. However, it is equally necessary to take into con-
sideration the fact that the candlepower from a so-called point
source or the "apparent candlepower per unit area" from a sur-
face source is not uniform in all directions in space. The fact
of the matter is that all practical sources omit light in such a
way as to appear non-uniform in brightness over the surface
when viewed from any one locality, and any one point on the
surface apparently varies in brightness when viewed from differ-
ent locations in space. It is impossible so to express the bright-
ness that its value will not be subjected to the changes here re-
ferred to.
If the surface were ideally perfect in its emission, its brightness
would be everywhere equal and uniform, and its apparent candle-
power would vary with the cosine of the angle of deviation of
the surface from normal to the line of vision ; that is the surface
would obey Lambert's "cosine law of emission." A surface
which is not ideally perfect in emission can be compared directly
with one which follows the cosine law of emission irrespective
of the units in which the outputs or appearances are expressed.
For convenience in calculation and purpose of comparison, it
is advantageous to express the outputs in terms of the lumens,
and the output density in terms of the lumens per unit area. It
is equally as convenient and logical to express the appearance in
terms of the luminous output density, selecting for the unit the
appearance of a surface emitting in accordance with Lambert's
cosine law. For this unit of appearance there has happily been
suggested the term "lambert," which is applied to the appearance
of a surface emitting one lumen per square centimeter in ac-
cordance with Lambert's cosine law of distribution and is equiva-
lent in appearance to that of a perfect matt surface of 100 per
cent, reflecting power illuminated with a density of one lumen
per square centimeter.
590 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
Although the introduction of the lambert brightness unit is of
recent date, it is noteworthy that its exact physical definition was
accurately presented before this society eight years ago in the
presidential address of Dr. Sharp, who stated therein that "the
brightness of a diffusely reflecting or transmitting surface is
proportional to the luminous flux which it emits per unit of area."
In view of the fact that the lambert unit is based on the surface
source conception, this method of expressing the brightness (that
is, the appearance to the eye) seems to me to be fundamentally
much more logical than the more common method involving a
reference to the point source conception. It is impossible to
derive an expression of brightness which does not in some way —
either directly or indirectly — involve the luminous output and
the surface area. That is to say, when the expression of bright-
ness includes a reference to the point source conception, it is
evident at once that there have been assigned to each infinitesimal
point source physical characteristics possessed exclusively by a
surface source. Simplicity in both conception and mathematical
analysis dictate the reference of all brightness expressions directly
rather than indirectly to surface sources and not to point sources.
Problems relating to both the output and the appearance of
practical lighting sources are greatly simplified when use is made
of the real surface source conception rather than the fictitious
point source conception.
Independent in every respect of the units employed in express-
ing the output and the appearance of a surface source, it is es-
sential to recognize the fact that only in the case of emission in
accordance with Lambert's cosine law is either the output density
on the appearance uniform over the surface. For simplicity in
calculation it is advantageous to assign such values to these
variables that the calculations will give results in practical accord
with the actual facts. The mean value of the output density can
evidently be found by dividing the total output by the total area
of the emitting surface ; this value is identical with the mean
effective value of the "appearance" or "brightness" of the same
source.
For all practical purposes the use of the mean effective value
(in space) of the brightness introduces errors no greater than
ILLUMINATION CALCULATIONS 591
those caused by substituting the mean effective value (in time)
of an alternating current for its cyclically varying value. That is
to say, problems in illumination from surface sources — and prac-
tically all sources are surfaces — are simplified by substituting the
mean effective value of the output density and appearance for
the actual values with their variations in space, in exactly the
same manner and to the same extent as equivalent problems in
alternating current phenomena are simplified by substituting the
mean effective value of the alternating current for the actual
values with their variations in time.
Let us carry the physical analogies somewhat further. The
substitution of the lumen conception for the candlepower concep-
tion has simplified illumination calculations just as the substitution
of the magnetic flux conception for the isolated magnetic pole
conception has simplified magnetic calculations. Moreover, the
use of the surface source conception rather than the point source
conception permits of the introduction of graphical methods of
solving problems in illumination equally as accurate and conven-
ient as the simplified circle diagrams now universally employed in
solving problems relating to the general alternating-current trans-
former.
To persons familiar with the time-honored laborious calculating
methods of the electrophysicist and with the short-cut but equally
accurate methods of the present-day electrical engineer, no ar-
guments need be presented in favor of the simplified methods of
solving problems in illumination other than the analogies just
outlined.
592 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
REPORT OF COMMITTEE ON PRESIDENT'S
ADDRESS.*
The committee appointed to report on the presidential address
of Dr. A. S. McAllister, on "Simplification of Illumination Cal-
culations," has to express its admiration for the lucid and con-
vincing expression of the views therein contained.
The underlying thought in the address is that illumination cal-
culations can be greatly simplified by discarding the usual method
of determining the illumination produced by the source on a
chosen plane by reference to the "inverse square" law and the
integrated "candlepower," and using the fundamental ratio ex-
isting between the "apparent luminous density" of the source
and the lumen density on the surface illuminated, which ratio
depends solely upon the solid angle subtended by the source when
viewed from the chosen plane. The use of the surface-source
conception rather than the point-source conception permits of the
introduction of simple-graphical methods for solving problems in
illumination.
The committee concurs with the views expressed in the address
and believes that the application of the method therein outlined
will assist materially in the simplification of illumination calcu-
lations.
Respectfully submitted,
C. H. Sharp,
E. P. Hyde,
P. S. Mieear,
L. B. Marks, Chairman.
* Presented at the ninth annual convention of the Illuminating Engineering Society
Washington, D. C, Sept. 20-23, 1915.
BENF0RD AND MAHAN : AVERAGE ILLUMINATION 593
A FLUX METHOD OF OBTAINING AVERAGE
ILLUMINATION.*
BY F. A. BENFORD, JR., AND H. E. MAHAN.
Synopsis: This method applies particularly to the calculation of
illumination on the floor or working plane of a large room or shop. The
basis of the method is the rating of lighting units by the percentages of
flux in the three zones o° to 300, 300 to 60°, and 6o° to 900. An index in
the form of an equilateral triangle is provided. Given the flux distribution
of any unit the index indicates a standard flux distribution of similar per-
centages in the three zones. A number of these standard distributions
have been solved and made up in the form of charts. By an inspection
of the proper chart the per cent, of the downward flux that falls within
any rectangle is readily found. By adding these percentages for the differ-
ent units of an installation, multiplying by the total downward flux of
one unit and dividing by 100 times the floor area the average direct
illumination is obtained.
The location of outlets and specifications for lighting equip-
ment have, in the past, followed, in most cases, rather empirical
rules. Those responsible for the lighting of buildings had very
little knowledge of the fundamental principles governing light-
ing, and hence followed the precedents and custom that had
grown up and which were based on architectural or structural
exigencies.
While the authors do not contend that structural conditions
should be ignored, they do feel that more consideration should be
given to the proper quantity and distribution of light than is
usually accorded them, and that questions relating to these items
should enter as factors in determining the most advantageous
position of outlets and sizes of units.
Feeling the need for a more rational method for checking
illumination designs and arriving at a reasonably accurate esti-
mate of the average illumination, the illuminating engineering
laboratory of the General Electric Co. has adopted the plan
described in this paper.
The designer of a lighting installation after studying the re-
quirements of his problem decides on a suitable type of unit and
the required intensity. He is guided thus far by consideration
of glare, color, power required, artistic and structural details,
etc., and arrives at a layout which satisfies these conditions.
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, 191 5.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
6
594 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Before passing on the final plans, however, he wishes to check
his completed design and determine whether or not the required
quantity of flux is being delivered on the working plane to pro-
vide the desired illumination intensity.
To the best of the authors' knowledge there are four methods
in use at the present time by which the average illumination of a
lighting installation may be calculated. Each has some peculiar
advantage, but none possess all the qualifications desired for
this class of work. These various methods are:
Average Effective Angle Method. — The light within some fixed
angle from the axis of the unit is assumed to be totally effective,
the remainder being wholly lost. A variation of this is to con-
sider a certain per cent, of the light from a given type of unit to
be useful, and changing this figure according as the walls and
ceiling are light, medium or dark in color. Usually in using this
method no account is taken of the size of the room, the spacing
of units or the height at which they are hung. The basis of the
method is the supposition that the units will be hung low in a small
room and high in a large room, there being a fixed relation
between height and area to be illuminated. But as the services of
the illuminating engineer are often asked for because of some
peculiarity or difficulty in the proposed installation, it is at once
evident that this method is of small use.
Hogner's Method. — Starting with the unit as a center, the
angular dimensions of the rooms are laid out. A table of con-
stants is provided and by multiplying the constants by the intensi-
ties of the source at io° intervals until the boundaries of the
room are reached, a figure for average illumination is ascertained.
This method contains the possibilities of a great deal of develop-
ment, but in the form with which the authors are familiar the
method is not elastic enough to meet all the various requirements.
The labor involved is an objection as is the probability of error
in handling the numerous decimal constants.
Illumination Curve Method. — The floor area is covered with a
network of illumination lines. The average illumination is found
by multiplying the illumination at a series of points by proper
area factors, adding, and then dividing the sum by the area of
the room. Considerable experience is required to place the illumi-
BENE0RD AND MAHAN : AVERAGE ILLUMINATION 595
nation lines in the best position, and a large amount of labor is
required for the various calculations. The results are ordinarily
very accurate, and have the great advantage of giving detailed
information about the illumination. If the lamps are irregular in
heights or spacing, the method practically fails on account of the
time taken for calculations.
Lumen Chart. — A lumen chart devised and used in this labora-
tory gives a reasonably quick and very accurate answer to prob-
lems in average illumination. The great objection to this method
is that the chart is a highly specialized device and it requires the
use of a draughting board.
In the above review the better methods are seen to be either too
long or too complicated and the quickest method is inaccurate.
The combination of quickness and accuracy in the same method
naturally presents difficulties, but most of these difficulties have
been overcome and a method arrived at that is nearly as quick
and simple as the first method, and exceeds all of the above
methods except the fourth in accuracy.
PRINCIPLES OF SOLID ANGLE FLUX CHARTS.
Several new departures have been made in the development
of these charts. First among these is the complete substitution
of lumens for candles, and second, a series of prototype or
standard distributions of flux have been made and substituted
for the actual flux distributions of the multitude of characteristic
curves in the laboratory files. The number of conditions that
had to be considered and taken care of were six in number:
1, character of distribution of flux from unit; 2, quantity of flux;
3, height of suspension; 4, length of area to be illuminated;
5, width of area to be illuminated; 6, location of unit with respect
to boundaries of area.
These charts apply only to symmetrical units and rectangular
areas. The hemispherical flux of the unit is regarded as ioo per
cent, divided into three thirty-degree zones, o°-30°, 30°-6o° and
6o°-90°. An equilateral triangle is used to index and classify
both the photometric distribution curves and the solid angle flux
charts. The sum of the distances from any point within an
equilateral triangle to the three sides is a constant for that tri-
angle. Making this constant ioo per cent., the length of the
596 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
three lines to the sides may then represent the percentages of
flux in three zones, thus giving every flux distribution a definite
point in the index triangle.
The triangle is divided into 166 hexagons, some of which are
not complete, see Fig. 1, and the central point of each is taken
as a "standard" flux distribution and an arbitrary number as-
signed it. The total flux up to 300, 6o°, and 900 for each stand-
ard curve was plotted and a smooth curve drawn through these
points furnished the data necessary to find the candle intensity
So
Fig. 1. — Index triangle. Solid angle flux charts.
9
at the various angles, as shown in the upper left hand corner of
Fig. 2. These distribution curves are not essential parts of the
method, but are given with each flux chart as a supplement to the
index.
These standard flux curves were solved to find the flux inci-
dent upon various rectangles and the results plotted on the charts.
The charts were then provided with several scales of lengths and
widths, so that a direct reading scale may be found for almost
any lamp height and for any size area.
BENFORD AND MAHAN I AVERAGE ILLUMINATION
597
The section of the index triangle in which the common distri-
butions fall is bounded roughly by lines drawn from hexagon 13
to 21, from 21 to 115 and from 115 back to 13. Sixty-one
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standard flux distributions are embraced in this area, and they
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distributions are shown in Fig. 2, Fig. 3, and Fig. 4.
598 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
APPLICATION.
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application to an actual installation, such as is described below.
The units were arranged as shown in Fig. 5, and their photo-
metric characteristics are given in Fig. 6.
The first step is to determine the index number of the unit.
BKNFORD AND MAHAN '. AVERAGE ILLUMINATION
599
The flux distribution, as obtained from the photometric curve, is
23.2 per cent, in zone o° to 300, 59.2 per cent, in zone 300 to 6o°
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600 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
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BENFORD AND MAHAN : AVERAGE ILLUMINATION
601
The actual distribution and the standard distribution are given
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rected to give the same total flux as the actual curve. It might
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seem that the difference between the two would lead to large
errors, but such is not the case. It will be shown later that the
error lies within practical engineering limits.
The room is considered to be divided into four quadrants about
602 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
each unit. Each unit is solved individually for the entire reading
plane area, the quadrants being taken one at a time. In Fig. 5
the quadrant below and to the right of the unit No. 1 has a
width of 4.25 ft. (1.3 m.) and a length of 5.7 ft. (1.74 m.). The
height of the unit above the reading plane is 6 ft. (1.83 m.).
In the lower right hand corner of the chart, Fig. 7, is a table
giving "height of lamp and scale constant." The large figures
are heights, and the small letter and figure above each indicates
the scales to be used and the values of the main divisions of the
same. Thus the height, 6 ft., is found in the first column, second
line of the tabulation. The "a" indicates that the upper "length
of quadrant" scale has a value of 10 ft. at the main division
marked "a," and also the left hand "width of quadrant" scale
has the same value at the point "a." With this information other
values of width and length are readily found.
TABLE I.
Lighting plan, Fig. 5.
Photometric distribution, Fig. 6.
Solid angle flux chart No. 64, Fig. 7.
Quadrant Per cent.
Units dimensions Feet effective lumens
No's. 1, 2, 5 and 6 4.25 x 5.70 10.5
5.70 x 11.25 16.5
11.25 x 25.10 22.2
4.25x25.10 14.0
63.2
Four units 4 x 63.2 = 252.8 per cent.
No's. 3 and 4 4.25 x 15.40 13.6
11.25 x 15.40 21.5
11.25 x 15.40 21.5
4.25 x 15.40 13.6
70.2
Two units 2 x 70.2 = 140.4 per cent.
Total effective flux from six units 393-2 per cent.
Total lumens per unit 638.0
Total effective lumens 2509.0
Reading plane area 15.5 feet x 30.8 feet 477-Q sq. ft.
Average illumination 5.26 foot-candles
The flux in the 4.25 ft. x 5.7 ft. quadrant may now be found by
finding where 4.25 comes on the width scale and noting where
this point is in relation to the two nearest arrow heads on the
opposite side of the line. In this particular case 4.25 ft. comes
BENFORD AND MAHAN : AVERAGE ILLUMINATION 603
almost exactly midway between two arrow heads, and the value
of effective flux will accordingly be found midway between the
two curves immediately to the left and directly above 5.7 ft. on
the scale of lengths. This value is 10.5 per cent., read on the
scale at the extreme left, and shows that 10.5 per cent, of the
flux from unit No. 1 falls within the quadrant in question.
The solution for the entire installation is shown in Table I.
The same "a" scales are used throughout, and the successive steps
are similar to the one illustrated above.
As a matter of interest and to serve as a check on the calcu-
lated results, the experimental room previously mentioned was
equipped with six outlets, and each provided with one 100-watt
clear tungsten lamp and porcelain, enamelled steel reflector. The
general arrangement of outlets is indicated in Fig. 5. The ceil-
ing consisted of press board; three of the walls were brick, the
fourth wall and floor of wood. The coefficients of reflection of
the various surfaces, obtained by means of a Nutting's reflec-
tometer, were as follows :
Per cent.
Floor 18.7
Press board 73-7
Brick walls 67.0
Wood wall 64.5
The room was divided into fifty stations as shown on the plan
of the room. Photometric observations were made at the center
of each station with a portable photometer and the entire number
averaged. In order to eliminate the direct light of the units from
the photometric screen as a means of determining the illumina-
tion due to wall reflection, diaphragms were constructed consist-
ing of blotting paper of approximately the same coefficient of
reflection as the room and mounted on portable stands. These
stands were moved about for each photometric station so as to
shield the photometer screen from the direct light coming from
the unit. The test results were as follows :
Foot-candles
Total direct and reflected light 7.04
Reflected light 1.65
Direct light 5-39
And, as a comparison with the calculated data we have,
.. . Calculated illumination 5.26
Ratio — — — r-rrj : — -. = = 0.98
Actual illumination 5.39
TRANSACTIONS
OF THE
Illuminating Engineering Society
Vol. X NOVEMBER 20, 1915 NO. 8
CODE OF LIGHTING.*
FACTORIES, MILLS AND OTHER WORK PLACES.
Article I. Daylight. — All buildings hereafter constructed must
be provided with adequate window area. Awnings, window
shades, diffusive or refractive glasses must be used for the pur-
pose of improving daylight conditions or for the avoidance of
excessive brilliancy wherever they are essential to these ends.
The windows, skylights, saw-tooth or other roof lighting con-
structions, are to be arranged with reasonably uniform bays, and
the daylight openings shall be so designed and proportioned that
at the darkest part of any work space, when normal exterior day-
light conditions obtain, there shall be available at least a minimum
intensity equal to three times the minimum intensities given in
Article V for artificial light.
(Note: The intensity requirements for daylight are higher
than those for artificial light because the physical condition of
the eye during the daytime is usually such as to require a higher
intensity of natural light for satisfactory vision than is required
at night under ordinary well designed artificial lighting systems.1)
Article II. Old buildings at present constructed and not having
adequate window area, must be provided with adequate artificial
light according to the following articles, so as to supplement the
natural light during normal daylight hours.
* For an amplification of the following articles of the code proper, see the Explanatory
Rules on page 608.
1 For detailed information on this daylight requirement, see Section I of the Ex-
planatory Notes on page 609.
606 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
Article III. All buildings, whether old or hereafter constructed,
must be provided during those hours of work when natural light
is insufficient or not available, with adequate artificial light ac-
cording to the following articles.
Article IV. — Adequate intensity of the light must be provided
for each class of work, both on a horizontal plane as well as on a
vertical plane passing through the work, according to Article V.
In all cases, however, glare on working surfaces is to be avoided
as it tends to reduce the visual efficiency of the workmen and to
increase the likelihood of accidents.
Article V. Artificial Light; Intensity Required. — The average
illumination intensity throughout any month actually measurable
in foot-candles on a horizontal plane through the work is to con-
form to the following table. Uncertain cases which arise as to
how to classify given manufacturing operations are to be left tc
the judgment of a lighting expert.
Class of work
Storage, passageways, stairways, and the like
Rough manufacturing and other operations . .
Fine manufacturing and other operations ....
Special cases of fine work
Where operations are performed on the sides of the work in
hand, they shall be classified according to this table, and if the
illumination is furnished from an overhead system, it shall pre-
ferably be not less than 50 per cent, of the foregoing values, when
measured on a vertical surface. If the illumination is furnished
by an individual lamp or by lamps close to the work, the intensity
shall conform to the minimum or desirable intensities required
in the foregoing table.
(Note: As a guide to inspectors and others, it may be stated
that with modern lamps roughly 1 candlepower per square foot
produces an effective illumination of 3 foot-candles when the
lamps are arranged according to the uniformly distributed over-
head system, with mounting heights ranging from 12 to 16 ft.
above the floor, and when the light is directed from said lamps
to the work in an efficient manner. A rough idea may thus be
secured of the candlepower per square foot necessary to conform
Minimum
foot-candles
intensity
Desirable
foot-candle
intensity
0.25
0.25- 0.5
1-25
1.25- 2.5
3-50
3-5 - 6.0
—
10.0 -15.0
CODE OF LIGHTING 607
to the foregoing table of intensities by taking one third of the
intensity values given in the foregoing table.)
Thus for fine manufacturing and other operations, the min-
imum foot-candle intensity is 3.5, which is approximately equal to
1.2 candlepower per square foot. The use of a portable photo-
meter or illuminometer, however, is recommended for the de-
termination of existing systems and all uncertain cases are finally
to be established by these instruments.
Article VI. Lamps and machinery jointly, are to be so arranged
as to avoid the casting of shadows over belts and other obstruc-
tions on important parts of the work, and the distribution of light
from the lamps should be such as to avoid sharp contrasts of light
and shade on the work.
Article VLT. Inspection and regular maintenance of all lighting
systems is required in spaces where work is being conducted, and
in no case must the lighting devices, whether windows, lamps
or auxiliaries such as globes and reflectors, be allowed to deter-
iorate, due either to dirt accumulations or to burned-out lamps,
more than 20 per cent, below the minimum intensity values
required by Article V.
Article VLII. Roadways, yards and places not usually fre-
quented must either be provided by illumination during working
hours when natural light is absent or partly absent, to make them
safe against accident to employees traversing or engaged in such
places, or a convenient control or controls must be placed at the
entrance to basements, stock rooms, and the like, so that a person
on entering can readily turn on the lamps beforehand.
Article IX. Stairways and passageways must be provided with
lamps and reflectors or shades carefully located so as to shed their
light generally over the entire space or spaces involved, and in
sufficient quantity to make the stairways and passages safe against
accident to employees traversing or engaged in such places. For
intensities see Article V.
Article X. Each working space is preferably to be illuminated
by lamps mounted overhead according to the system of general
lighting, in preference to individual lighting. The overhead
method of lighting, besides possessing many other advantages,
also tends to reduce dark spots throughout the floor area, a
608 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
feature usually objectionable with the use of individual lamps.
This particular Article is not an absolute requirement, but a sug-
gestion enforceable at the discretion of a lighting expert.
Article XI. Auxiliary lighting should be provided in all large
work spaces, such lamps to be in operation simultaneously with
the regular lighting system, so as to be available in case the latter
should become temporarily deranged.2
EXPLANATORY RULES.
The foregoing articles are supplemented by the following
rules, which will aid in the observance of the requirements con-
tained in the articles; tend to reduce eye trouble and accidents;
and help in the securing of favorable results in planning lighting
systems.
1. Lamps should be equipped with reflectors or shades for
minimizing glare and economizing light. Bare lamps should not
be used except in rare cases and then only when out of the line of
vision.
2. As a general plan, mount the lamps high and out of the
ordinary line of vision.
3. Although the types of reflectors and shades, and reflector
and shade holders or fitters on the market are numerous, it is
recommended that the holder or fitter, as well as the reflector or
shade be selected with reference to placing the light source at the
proper point in the reflector or shade so as to eliminate glare, due
to exposure of the light source, and also for the purpose of di-
recting the light from the lamp effectively to the work, that is,
for obtaining a distribtuion of light which meets the desired re-
quirements.
4. Light thrown vertically downward is not the only important
component of the resulting illumination. The sides of machinery,
machine tools and work, as well as horizontal surfaces often re-
quire good light.
5. Control few lamps in each group so that lamps not needed
may be turned off conveniently.
6. Keep windows, lamps and reflectors clean since large losses
of light result from the accumulations of dust and dirt.
2 See Auxiliary Systems for Safety, Section XVI of the Explanatory Notes on page 640.
CODE OF UGHTIXG 609
7. Provide a maintenance department if the shop is large
enough to warrant it, so that all the items associated with the
upkeep of the lighting system may be cared for systematically.
8. Keep ceilings and upper portions of walls a light color for
the purpose of rendering both natural and artificial lighting more
efficient and better diffused. The lower portions of walls should
be a color which is restful to the eyes, preferably a medium tint,
typified by the tint known as factory green, or a rather dark
shade of yellow. Other medium tones are also available.
EXPLANATORY NOTES.
Section I. Daylight. — Adequate daylight facilities through
large window areas together with light cheerful surroundings,
are highly desirable and necessary features in every work place,
and they should be supplied through the necessary channels not
only from the humane standpoint, but also from the point of view
of maximum plant efficiency.
Importance of Daylight. — The unusual attention to gas and
electric lighting in factories, mills and other work places during
the past few years ; the perfection of various lamps and auxiliaries
by means of which an improved quality and quantity of lighting
effects are obtained ; and the care which has been devoted to in-
creasing the efficiency in various industrial operations ; — all go to
emphasize the many advantages and economies that result from
suitable and adequate window space as a means for daylight in
the proper quantities and in the right directions during those por-
tions of the day when it is available.
Three Considerations. — Three important considerations of any
lighting method are sufficiency, continuity and diffusion. With
respect to the daylight illumination of interiors, sufficiency
demands adequate window area; continuity requires (a) large
enough window area for use on reasonably dark days, (b) means
for reducing the illumination when excessive due to direct sun-
shine, and (c) supplementary lighting equipment for use on par-
ticularly dark days and especially towards the close of winter
days; diffusion demands interior decorations that are as light in
color as practicable for ceilings and upper portions of walls, and
of a dull or mat finish in order that the light which enters the
windows or that which is produced by lamps may not be absorbed
6lO TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
and lost on the first object that it strikes, but that it may be
returned by reflection and thus be used over and over again.
Diffusion also requires that the various sources of light, whether
windows, skylights or lamps, be well distributed about the space
to be lighted. Light colored surroundings as here suggested result
in marked economy, but their main object is perhaps not so much
economy as to obtain a result that will be satisfactory to the
human eye.
Requirements. — The following requirements may now be listed
for natural lighting:
i. The light should be adequate for each employee.
2. The windows should be so spaced and located that daylight
conditions are fairly uniform over the working area.
3. The intensities of daylight should be such that artificial light
will be required only during those portions of the day when it
would naturally be considered necessary.
4. The windows should provide a quality of daylight which will
avoid a glare due to the sun's rays and light from the sky shining
directly into the eye, or where this does not prove to be the case
at all parts of the day, window shades or other means should
be available to make this end possible.
5. Ceilings and upper portions of walls should be maintained
a light color to increase the effectiveness of the lighting facilities
from window areas. The lower portions of walls should be
somewhat darker in tone to render the lighting restful for the
eye. Factory green or other medium colors may be used to good
effect.
Classification. — Means for natural lighting may be classed
under three broad divisions as follows :
(a) That case in which the windows are located on the sides
of the building or in the framework of saw-tooth construction,
where diffused light from the sky reaches the work during a large
portion of the day.
(b) That case in which windows are located overhead on a
horizontal or nearly horizontal plane in the form of skylights,
thus furnishing direct light from the sky during a large portion
of the day.
CODE OF LIGHTING
6ll
(c) That case in which prismatic glass takes up the direct light
from the sky and redirects it into the working space.
Method (a) is, of course, the most common of the three, and
it may be noted that the saw-tooth or other roof lighting con-
structions have become very popular and result in an excellent
quality and quantity of light for given window areas provided
the size and location of windows are in accord with modern
practise.
Increasing the Value of Floor Space. — Adequate and well dis-
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PLAN
Fig. i. — Diagram, of a large office with windows on one side only.
tributed natural light means that certain portions of the floor
space which ordinarily would not be available for work, are con-
verted into valuable manufacturing space. In a general way,
therefore, the average factory, mill or other work place, if prop-
erly designed, should possess natural lighting facilities which
produce the best practicable distribution of daylight illumination.
Wide Aisles. — With low ceilings and very wide aisles, work-
men located at the central portion of the building must sometimes
depend for their natural light on windows located at a consider-
able distance away from their working position. In these cases
6l2 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
it may be impossible, in general, to depend altogether on daylight
over an entire floor space, even at those times of the day when
daylight conditions would be entirely adequate under other cir-
cumstances. This statement applies to side windows rather than
to skylights or to saw-tooth construction. Fig. I illustrates this
feature.
Varying Conditions. — In a case of this kind, employees located
next to the windows are furnished with suitable daylight in the
early morning and towards the latter part of the afternoon, the
upper portions of the windows being particularly serviceable in
lighting areas at some distance away from the windows. A
southern exposure, however, results in such excessive light from
the sky during the middle of the day, that heavy shades are
nearly always pulled down so as to cover the entire window area.
This plan makes it necessary to use artificial light throughout the
larger part of the office during the brightest portion of the day,
and reduces the daylight at those points where it would supposedly
be the best, namely, near the windows. Here the location of
the windows is a large factor in the excellence of the daylight
conditions, but the manipulation of the shades is perhaps even
more important. To avoid such a difficulty, adjustable translu-
cent upper window shades with adjustable opaque lower shades
might be employed.
Upper Portions of Windows. — It should be further noted in
this illustration that the upper portions of the windows give a
reduced illumination in proportion to their areas, to the floor
space near them. In rooms of moderate size, therefore, the
windows should be placed as near the ceiling as practicable.
When the sun shines through windows so located, the direct light
must be reduced or diffused. This may be accomplished by the
use of ribbed glass in ordinary factory and mill buildings, and
in offices by the use of translucent sun shades or awnings.
Tempering the Light. — The light due to the sunshine on such
shades and awnings will be as bright as ordinary skylight if the
shade is well chosen, and the ribbed glass will be still brighter.
If the windows are large, the illumination is likely to be too great
near the windows as previously pointed out and it must be re-
duced- This should not be done, however, by pulling down an
CODE OF LIGHTING
613
opaque shade over the top of the windows because the top por-
tion of the window is the part that is particularly needed to give
light to the interior of the room. The better scheme is to employ
an opaque shade which should be raised from the bottom of the
window. This will reduce the illumination near the window
without affecting it over the interior of the room to any marked
degree.
Bench Locations. — Fig. 2 shows how benches are commonly
located with respect to windows, so that the light received on the
work may be most satisfactory. This sets a certain limitation
upon the possible arrangement of the work over the floor space,
depending on the way the daylight is furnished to the floor area.
/////////^/////^////////////////////////////////I
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PLAN
Fig. 2. — Diagram showing benches located with respect to the windows so as to receive
the natural light advantageously.
This limitation can be eliminated almost completely in the case
of artificial light through a uniform distribution of lamps over-
head. This statement applies to those cases where natural light
is transmitted through side windows, and includes a feature
specially noticeable in buildings of more than one story. In con-
trast, the work may be arranged almost independently of the
natural light in buildings where the natural light is furnished
by overhead windows or through the means of saw-tooth
construction.
Windoiv Glasses. — Both translucent and clear glass are em-
ployed for factory and mill windows. There is a slight reduction
in the transmitted light through ordinary translucent wire glass,
614 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
but it is often required by insurance regulations for a reduction
in the fire risk where a given building is located in close proximity
to other buildings. Wire glass is also used quite generally with
steel window frames, here being an added protection from the
standpoint of fire risk. Wire glass may be obtained in clear
form, but its expense in contrast to the translucent form is such
as ordinarily to prohibit its use for industrial purposes.
Wire Glass. — Wire glass, also known as ribbed glass, should
be used and is advocated for practically all factory and mill win-
dows where prisms are not required. Wires of rather open
mesh cause so little reduction in light as to warrant no mention
of this feature. Special care should be taken to get such glass
as is smooth both on the flat side and on the ribbed side to facili-
tate cleaning. Wire or ribbed glass gives better diffusion than
plain glass.
Prism Glass. — Where the sky outside of the windows is ob-
structed by buildings, prism glass is recommended if the room is
deep. Different kinds of prisms cannot be used to advantage
interchangeably. The amount of prism glass required in any
case depends much upon the surroundings and to obtain excel-
lent results, of which such glass is capable, it must be used
intelligently.
Skylights. — Skylights are sometimes installed in long narrow
continuous strips in a sloping roof. The ribs of the ribbed glass
are generally so arranged that it is convenient to make them at
right angles to the length of the strips. The result is that the
sunshine is diffused by the ribs over a narrow area parallel to
the strip of skylight, thus lighting one part of the room much
more brilliantly than the remainder. If the ribs are installed to
run parallel to the strips, they will give a much more general dis-
tribution of the sunlight. In the foregoing, the word strip refers
to the long belt of skylight and not to the individual sheet of
glass. Ribbed glass in vertical windows should generally be
placed with the ribs horizontal. They thus roughly fulfill some
of the functions of prisms.
Dirt Accumulations. — While translucent wire or ribbed glass
reduces the amount of light transmitted through the windows,
the roughness of the outside surface of such glass often causes
CODE OF LIGHTING 615
accumulations of dust and dirt, which are more to blame for the
reduction of transmitted light in some cases than the translucent
nature of the glass itself. Remedies of this difficulty are to
secure smooth glass and to restort to frequent cleaning.
Wire Glass as a Safeguard. — Wire glass for skylights is, of
course a practical necessity as a safeguard against accidents due
to accidental breakage of the glass or due to objects falling on
top of the glass.
Calculations for Natural Light. — In certain typical localities,
the average brightness of the sky during business hours is about
250 candles per square foot. This is probably a fair average
value for the entire United States. The lower or minimum value
of sky brightness, excluding particularly stormy days, may be
taken as about 100 candles per square foot. Allowing for a
reduction of 25 per cent, for losses in the windows themselves,
the brightness of the sky as seen through a window becomes
equal to a minimum of say 75 candles per square foot in any
directions from which the sky can be seen through the windows.
This brightness value if multiplied by the part of the window
area through which sky is visible from a given point in the work
space gives the available candlepower through the window in
question, and this candlepower is then divided by the square of
the distance between the given point and the window to obtain
the foot-candle intensity of the illumination at the given point.
Method illustrated. — To illustrate this method, consider a hall-
way 40 ft. long, lighted by a window 5 ft. by 5 ft. at one end,
with the sky visible from the darker end of the hall through the
upper half of the window only. The illumination at the dark
end of the hall will then be equal to :
5 X 5 X 0.5 X -~- = 0.58 foot-candles,
1,600
under the assumed window brightness of 75 candles per square
foot. The 1,600 in this calculation results from the square of
40 ft., the length of the hall, or in other words the distance from
the point considered to the window ; and the factor 0.5 takes into
account the fact that the sky is visible through only one half of
the window area from the point considered.
Checking the Intetisity. — The intensity is not sufficient at this
6l6 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
darkest part of the hall since the requirements of Article I of
the Code proper call for three times the minimum values given
in Article V, and the minimum value given in Article V for
passageways is 0.25. Three times this value is 0.75 which is
somewhat greater than the value found in this calculation. The
window area must therefore be increased in size by about 50
per cent., or if this is impossible or impracticable, the hallway
must be provided with artificial light at those points where the
natural light falls below the requirement.
Calculation for a Skylight. — As another illustration, assume
that fine manufacturing work is to be performed under a skylight
20 ft. above the work. If the brightness is assumed to be 75
candles per square foot as before, the minimum intensity must
be 3 X 3-5 foot-candles, that is, 10.5 foot-candles, based on the
requirements of Article I of the Code. The window area must
then equal :
400
10.5 X — - = 56 sq. ft.
Part of Window Area to Consider. — It is important in esti-
mating the illumination of any work room to consider only that
portion of the window area through which clear sky is visible,
provided the window is equipped with ordinary clear glass.
Sunshine Not Desirable. — In all the work of providing natural
light, it should be kept in mind that direct sunshine in itself, from
the illumination standpoint but irrespective of sanitary condi-
tions, is not wanted. The idea that sunshine is the important
item is a common but an erroneous impression. For example,
in saw-tooth construction, the windows do not face the south to
get all the sunshine possible, but they face the north to exclude
the sunshine. Ordinary windows, on the other hand, face all
directions because not enough light can be distributed to interiors
from north windows alone. Windows on the other than north
fronts admit sunshine to be sure, and this makes sun shades and
awnings necessary to exclude the excessive brightness.
Section II. Value of Adequate Illumination. — Factory and mill
owners are concerned in the matter of securing the largest output
for a given manufacturing expense. An improved machine tool
capable of increasing the product for given labor costs is most
CODE OF LIGHTING 617
attractive, provided its first cost is within returnable limits out of
the larger profits. Improved small tools, better methods of hand-
ling material, adequate crane service, fire protection, good shop
floors, accurate and efficient time-keeping methods, and similar
items, vitally concern the shop manager; money is expended to
realize excellence in these features because they afford increased
economies and protection, thus resulting in a higher efficiency of
the plant.
Energy Consumption a Minor Item. — Many arguments leading
to the sale of gas and electric lamps for use in factory and mill
buildings are based on reducing the lamp operation cost by sub-
stituting a new for an older system. Arguments of this kind are
of value, however, only when such a reduction in operation cost
can be effected without sacrifice in the adequacy of the illumin-
ation. It would be a poor policy, in the extreme, to argue a sav-
ing in energy consumption by the substitution of one type of
lamp for another on a basis of equal candlepower in both old and
new systems.
Effect of Good Light on Production. — Arguments of a con-
vincing nature, which insure to the factory or mill manager an
increased output through improved illumination service, are of
importance and even greater at times than reductions in the
cost of illumination for the same quantities of light. In view of
the fact that resulting advantages of superior illumination on
increased output are apt greatly to exceed economies in operation
cost as regards the lighting system, it is a distinct advantage to
direct and hold the attention on the former rather than on the
latter. This statement will be more apparent when interpreted
into definite items as follows :
Advantages of Good Light. — While the necessity of good nat-
ural and artificial light is so evident that a list of its effects may
seem commonplace, these same effects are of such great im-
portance in their relation to factory and mill management, that
they are well worth careful attention. The effects of good light,
both natural and artificial, and of bright and cheerful interior
surroundings, include the following items:
1. Reduction of accidents.
2. Greater accuracy in workmanship.
6l8 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
3. Increased production for the same labor cost.
4. Less eye strain.
5. Promote better working and living conditions.
6. Greater contentment of the workmen.
7. More order and neatness in the plant.
8. Supervision of the men made easier.
In this list it will be noted that items 4, 5, 6, 7 and 8 all have a
bearing on accident prevention.
Interpreting the Advantages of Good Light. — While the major
consideration in the eyes of the factory or mill owner is un-
doubtedly and quite naturally the money value of good light in
the larger return of both quantity and quality of work which may
result from the installation of a superior as compared with an in-
ferior lighting system, it should be noted that it is very difficult
to interpret into dollars and cents the value of good light made
possible by such returns. This difficulty is due to the necessity
of keeping all conditions in a factory or mill section absolutely
constant while varying the amount of illumination from poor to
good conditions, in an effort to determine the output and its de-
pendency on the lighting facilities. As accurate data becomes
available, giving the increases in production for certain specific
improvements in artificial lighting, it will doubtless prove helpful
to a proper interpretation of adequate light and its worth to any
plant.
The eight foregoing points are emphasized as forming the
most important features in the problem of good lighting. Al-
though difficult to interpret into money values, and somewhat in-
tangible, they are indisputable arguments in favor of the best
available illumination from the standpoint of the factory or mill
owner.
Practical Example. — Continuing from the manufacturer's point
of view, it may be said that certain assumptions as to energy cost,
cleaning, interest and depreciation, show that the annual opera-
tion and maintenance cost for the illumination of a typical shop
bay of 640 sq. ft. area, may be taken at $50.00. If five workmen
are employed in such a bay at an average wage of say 25 cents
per hour, the gross wages of the men in such a bay, plus the cost
of superintendence and indirect shop expense, may equal from
CODE OF LIGHTING 619
$5,000, to $7,000 per annum. In a case of this kind, therefore,
the lighting will cost from 7/10 to 1 per cent, of the wages, or the
equivalent of less than 4 to 6 minutes per day. We may roughly
say that a poor lighting system will cost at least one half this
amount (sometimes even more through the use of inefficient
lamps and a poor arrangement of lamps), or the equivalent of
say 2 to 3 minutes per day. Nearly all factories and mills have at
least some artificial light, hence, in general, if good light enables
a man to do better or more work to the extent of from 2 to 3 min-
utes per day, the installation of good lighting will easily pay for
the difference between good and bad light, through the time saved
for the workmen.
Actual Losses. — Superintendents have stated in actual instances,
that due to poor light their workmen have lost much time, some-
times as much as from one to two hours per day or certain days.
If good light will add an average of say one-half an hour per day
to the output, these 30 additional effective minutes represent an
increase in output of 5 per cent., brought about through an ex-
penditure equal to l/> oi 1 per cent, of the wages for improved
lighting, or a saving equal to ten times the expense.
Safety. — While these features are of special interest in the
eyes of the manufacturer, the principle item to consider, perhaps,
from the legislative side of the question, is the necessity of an
act or acts to provide employees of workshops with proper and
sufficient illumination from the standpoint of safety. The legal
aspect of the safety question in its relation to illumination in fac-
tory and mill buildings is a topic of unusual importance.
Section III. Old and New Lamps. — The inadequate means avail-
able for illumination by artificial methods in the past have con-
tributed to the slowness of an appreciation of the features of
artificial light which influence the working efficiency of the eye.
Open flame gas burners, carbon incandescent and arc lamps,
practically the only illuminants available ten years or so ago, play
but a small part in the present approved methods of factory and
mill lighting.
New Lamps. — The large variety of comparatively new lamps
available for factory and mill lighting includes the mercury vapor,
metallized filament, tungsten, gas filled tungsten, metallic flame
620 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
or magnetic arc, the flame carbon arc, the quartz mercury vapor,
and various types of gas arc lamps. Remarkable improvements
have thus been made in both the electric and gas lighting fields,
the same general rules of applying the lamps covering both of
these fields. Possibilities in factory and mill lighting are now
attainable which, before the introduction of these new lamps,
were either unthought of or impossible. Consideration of the
eye as a delicate organ, together with the new ideas of the items
which affect its comfort and efficiency, have resulted in establish-
ing certain principles in illumination work, and have directed at-
tention naturally and in a growing manner to the proper use and
application of these new lamps.
Section IV. Effects on Factory and Mill Lighting Produced
by Modern Lamps. — With the introduction of these new gas and
electric lamps, broader possibilities have been presented in fac-
tory and mill lighting. The use of units of sizes adapted to the
purposes, allows results which it has been hitherto impossible to
obtain satisfactorily, either by the arc lamp, carbon filament or
open flame gas burner, formerly available.
New Possibilities. — It is evident that the introduction of the
many new lamps has made possible what may be termed a new
era in industrial illumination, a distinctive feature of which is
the scientific installation of the lighting units, suiting each to the
location and class of work for which it is best adapted. Before
the availibility in recent years of medium sized gas and electric
units the choice of the size of unit for a given location was often
no choice at all. In many cases, due to small clearance between
cranes and ceilings, or other conditions making it necessary to
mount the lamps very high above the floor, but one size or type
of unit was available, the carbon filament or open flame gas
burner in the former, and the arc lamp in the latter case.
Low Ceilings. — For low ceilings, up to 18 ft., the use either of
carbon filament, open flame gas burner, or arc lamps resulted
usually in anything but uniform light over the working plane, and
often produced merely a low general light which was practically
useless for the individual machine. In such instances, individual
lamps had to be placed over and close to the machines. With this
arrangement, relatively small areas are lighted by each lamp, and
code; of lighting 621
the metal shades usually employed, serve only to accentuate the
"spot lighting" effect. Such a form of illumination for factory
and mill work is unsatisfactory and inefficient, but as stated, was
in the past, in many cases, the only available scheme. The ab-
sence of lamps of the proper size is no longer an excuse for the
existence of such conditions in industrial plants.
Section V. General Requirements of Artificial Lighting. — The
following requirements for factory and mill lighting are made
all the more important by the peculiar limitations and the wide
variety of conditions to be found in factory and mill buildings
and in factory and mill work :
1. Sufficient illumination should usually be provided for each
workman irrespective of his position on the floor space.
2. The lamps should be installed and selected so as to avoid eye
strain to the workmen.
3. The lamps should be operated from sources of supply which
will insure reliable illumination results, particularly on account of
the demoralizing effect produced by intermittent service, just
when the light may be most needed.
4. Adequate illumination should be provided from overhead
lamps so that sharp shadows may be prevented as much as possi-
ble, and in such measure that individual lamps close to the work
may be unnecessary except in special cases.
5. The type and size of lamp should be adapted to the partic-
ular ceiling height and class of work in question.
6. In addition to the illumination provided by overhead lamps,
individual lamps should be placed close to the work if they are
absolutely necessary in the eyes of a lighting expert, and in such
cases the lamps should be provided with suitable opaque re-
flectors.
These requirements may now be met by means of the new
types of gas and electric lamps, one type of which can usually be
found for practically each factory and mill location, specially
adapted to the general physical conditions of the location as typi-
fied by the clearance between cranes and ceiling and other similar
items.
Section VI. Overhead and Specific Methods of Artificial Light-
ing.— Factory and mill lighting may be classified under two
622 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
general divisions : first, distributed illumination furnished from
lamps mounted overhead; and second, specific illumination fur-
nished by individual lamps located close to the work. For practi-
cal purposes this classification is sufficient. In numerous cases a
combination of these two methods becomes necessary.
Mounting the Lamps High. — Where the lamps are high enough
to be out of the line of ordinary vision, and are of a size and so
spaced as to furnish illumination at any position of the floor
where work may be carried on, the system is referred to as the
overhead method of lighting. This method has many advantages.
Its general adoption, which has been somewhat slow, has in-
creased with the appearance of the many new types of lamps and
with the growing appreciation of the value of good lighting.
Where a small amount of general or overhead lighting is
coupled with specific lighting from individual lamps, a large part
of the floor space in many shops is in relative darkness, and much
dependence must be placed on the hand lamps close to the work.
The small number of overhead lamps generally used in such
cases, furnishes merely a small amount of additional illumination
over the floor space which is not sufficient to be of much value.
However, where sufficient intensity is provided by general illum-
ination, this is pften a very effective means of lighting a large
work-room.
Low Ceilings. — Locations with low ceilings, until recently,
have been lighted by the individual hand lamp method, because
the old carbon filament lamps, being of low candlepower, could
not well be used close to the ceiling, while the old type of arc
lamp was often impracticable, due to its large physical size, as
well as its relatively high candlepower. This statement is sub-
ject to some modification, because low candlepower units have
sometimes been used in clusters for low ceilings as a compromise
between a single small or a single large unit, this scheme being,
however, usually insufficient and unsatisfactory in comparison
with modern methods of lighting. In a particular manner, there-
fore, suitable illumination has been difficult with low ceilings.
New types of gas and electric lamps have a range of candle-
power from very low to very high values, and the overhead
system with the elimination of individual lamps is thus possible;
CODE OF LIGHTING 623
in other words, a size of gas or electric lamp may now be selected
from a large available list of sizes for nearly every factory or
mill condition.
Section VII. Various Locations Illustrated.3 — Figs. 3 to 12 in-
clusive are given to indicate how the problem of adequate illu-
mination has been solved in a number of actual instances, and the
following notes apply to some of the considerations involved.
There are two main items to consider in deciding for or against
high candlepower lamps for the factory or mill. First, how high
are the lamps to be mounted; and second, will the light at any
given point on the machines or other operations be satisfactory
if it comes from a few lamps or should it come from many
sources ? If the ceiling or overhead construction is under 16 ft,
lamps of high candlepower can hardly be used in sufficient num-
bers to produce uniform illumination over the floor space. If
they are to be mounted at a height between 16 and 25 ft., it is
largely a question of whether light from a relatively few lamps
will produce satisfactory results. For mounting heights over
25 ft., lamps of high candlepower possess some advantages, chief
of which is their large volume of light for given energy consumed,
always provided the light is effectively directed towards the floor.
Three Groupings. — These three groupings by mounting heights
are conveniently shown in Figs. 15, 16, 17 and 18. In Fig. 15,
a single shop bay with a ceiling height of 12 ft. is shown as typical
of the first grouping. The single high candlepower lamp fur-
nishes approximately the same amount of light to the machines
as do the eight small lamps. Note, however, that the illumination
from the large lamp is not nearly as uniform as that from the
small lamps, although the spacing of both the small and the large
lamps as represented in this illustration is typical of many actual
installations. Note also, that the shadows cast by the large lamp
at certain portions of the floor space must be so marked as to
make the illumination it furnishes very inferior in this respect to
the illumination from the smaller lamps, because of their larger
number.
Here, if the number of large lamps for the given floor area be
3 Figs. 3 to 12 inclusive are, in general, arranged in the order of their mounting
heights. The low mounting heights are shown in the earlier illustrations and the higher
mountings in the later views.
624 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
increased in an endeavor to make the illumination more uniform
and to reduce the shadows, the expense, as compared with that for
smaller lamps, makes the large lamps a very unfavorable proposi-
tion. These two features are the basis for stating that in general
large lamps are not desirable for mounting under 16 ft., and an
analysis of conditions, together with a careful and unbiased com-
parison with the illumination produced by smaller lamps, will
nearly always bear out this conclusion.
Second Grouping. — In Fig. 16, a 20 ft. ceiling has been selected
as typical of the second grouping, a single shop bay being shown.
Here the work is assumed to be rough assembly, mostly on hori-
zontal surfaces, and the single high candlepower lamp, besides
giving more nearly uniform illumination, because the light is dis-
tributed more broadly due to the increased height, is correspond-
ingly more satisfactory as to shadows produced by the large lamp
in the preceding illustration (Fig. 15), on account of the improved
direction in which much of the light reaches the work. In this
case, the arrangement of both large and small lamps is typical of
many existing installations.
In Fig. 17, however, although the height is the same as in
Fig. 16, the work is quite different, being conducted on the inside
of large vertical tanks. It would obviously be impossible to
perform this work by the light from the single large lamp as well
as with that from the larger number of medium sized lamps, even
if the actual amount of light from each was the same, on account
of the poor direction of the light at certain positions of the work
from a single unit in such a case. The medium sized lamps
furnish approximately the same quantity of light and yet no
matter where the tanks may be placed, they will receive consid-
erable light from the medium sized lamps directly over or nearly
over them, at least far more than is apt to reach them from a
single unit in every other bay (the assumed arrangement of the
large lamps).
For this second grouping of mounting heights, then, the. large
lamp may or may not be adapted, depending on whether the
reduction of shadows is of much importance, as is the case in
Fig. 17. The large lamp is, however, more likely to be satisfac-
tory here than in the first case (Fig. 15), because of the better
Fig- 3- — Night view of a rather low factory section showing tungsten lamps of the 250-watt
size mounted 12 ft. above the floor. Note the original individual lamps over the machines.
Fig. 4.— Night view showing mercury-vapor lighting in low factory section. The lamps
are about 12 ft. above the work. Note the comparative absence of shadows.
Fig. 5.— Day view of a gas lighting installation in a low factory section. This photograph shows
merely the general arrangement of lamps and gives no idea of the illumination effect.
Fig. 6.— Night view of a planing mill showing an installation of 250-watt tungsten lamps with a
16 ft. mounting. Note the excellent distribution of the light and the comparative absence
of shadows. This is an example of the overhead method of lighting.
Wn-W"
Fig. 7. — Night view of a boiler shop.
Fig- s- — Day view showing arrangement of gas lamps in a medium high factory space.
Note the pierced reflectors over the machine tools near the center of the picture.
Fig. 9.— Night view of factory section with relatively high mounting of 250-watt tungsten lamps.
The lamps are 20 ft. above the floor. Note the excellent distribution of the light and the
shielding effect of the girders which serve to reduce the glare as one looks down the aisle.
Fig. 10.— Night view of arc lamp installation with 40 ft. mounting at center of picture,
and 20 ft. at sides. Excellent distribution.
UH
Fig. ii. — Day view of relatively high section, showing a system of gas lighting.
Fig. 12. — High section showing a system of mercury-vapor lamps. Note the excellent
distribution of light over the floor area.
Fig. 13.— Excessively bad lighting. Bare lamps produce a glare which is harmful
and renders the illumination very ineffective. Compare with Fig 14.
Fig. 14.— Example of good tungsten lighting with metal reflectors. Note the row of lamps
near the ceiling for producing general illumination. This is known as combined general
and localized illumination. Compare with Fig. 13.
CODE OF LIGHTING
625
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626 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
distribution of the light due to the higher mounting, a fact made
evident in Figs. 15 and 17 on account of the decreased number
of small lamps and the increase in their size made possible in
Fig. 17 as compared with Fig. 15, where the mounting is lower.
By the same line of argument, it can be shown that for higher
mountings, large lamps are still more likely to prove satisfactory.
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Fig. 18. — Diagram showing the use of large lamps for a mounting height of 50 ft.
In Fig. 17, the number of large lamps might have been increased
for the given floor area, but to have done so would mean that
the cost for the lamps themselves and for the energy and upkeep
to maintain them would be excessive in comparison with the
smaller types of lamps.
Third Grouping. — In Fig. 18, the third grouping of mounting
heights is shown with the lamps about 50 ft. above the floor. In
CODE OF LIGHTING
62J
this illustration the distribution of the light from the large lamps
will be far more satisfactory both for flat and tall work than in
the two preceding cases. It will be noted further that the in-
creased height of the lamp causes the light to fall in such direc-
tions as to evenly distribute it over the entire floor space taken
care of by this one lamp in much better shape than for the lower
mounting heights. (See also Figs. 19 to 21 inclusive.)
Section VIII. Lighting Circuits for Electric Lamps and Supply
Mains for Gas Lamps. — The question of lighting circuits is men-
tioned here with particular reference to factory and mill condi-
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Fig. 19. — This shows a very poor arrange- Fig. 20. — This illustration is to be compared
ment of artificial lighting by means of with Fig. 19. It indicates an improved
large lamps mounted too close to the floor. scheme over that shown in Fig. 19, made
Compare this poor lighting scheme with possible by the use of smaller lamps
the improved plan in Fig. 20.
tions, where motor loads are apt to be large in comparison to the
energy consumption of electric lamps which are in service. In
some cases, the proportion of motor load to lighting load is in
the ratio of 10 to i, in others 7 to 1, and so on, and the varying
demands on the circuits by motors may greatly affect the lamps.
Hence it is important to maintain strictly separate supply circuits
for the lamps in order to avoid varying voltage which is apt to
result if the motors are connected to the same circuits with the
lamps.
628 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
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CODE OF LIGHTING 629
Constant Voltage. — In addition to the superior illumination re-
sulting from lamps supplied from constant voltage mains, some
types operate with longer life or very much better mechanically
when supplied with constant voltage than otherwise. These
features will therefore generally more than offset the somewhat
greater cost of maintaining separate circuits for each class of
service. In like manner and for similar reasons, it is advisable
to place gas lamps on supply lines separate from those delivering
gas for power purposes.
Section IX. Control of Lamps and Arrangement of Switches. —
The control of lamps in factory and mill lighting is important in
all cases, but specially so where a large number of lamps is used
in preference to a small number for a given floor area. For ex-
ample, where an overhead system of tungsten lamps of small size
is used, a large number will, of couse, be necessary for a given
floor area, and in such cases the number of control circuits may
at times seem excessive when planned out for sufficient flexibility
of operation. Such circuits, however, in rendering the system
more flexible, will be more than paid for by the saving in energy
and maintenance due to the turning out of lamps not needed in
certain sections of the factory or mill, provided the number of
hours per day during which the lamps are used on the average is
relatively large, and the differences in daylight intensities over the
floor area is also relatively large.
Control Parallel to Windows. — The lamps most distant from
the windows will usually be required at times when the natural
light near the windows is entirely adequate, thus making it an
advantage to arrange the groups of lamps in circuits parallel to
the windows. The advantage of this method is further apparent
when it is considered that if the lamps are controlled in rows per-
pendicular to the windows, all lamps in a row will necessarily be
on at one time, while a portion only may be required.
Practical Case. — The foregoing statement may be developed
into a definite proposition. Thus, to install a single switch may
involve say $5.00 as its first cost. If ten lamps are to be con-
trolled from a single switch, these ten lamps must obviously either
all be turned off at a time or all turned on at a time. An addi-
tional switch at a cost of $5.00 will permit either half of these
63O TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
ten lamps being turned off, if not required at certain times when
the remaining five are needed. This extra switch may or may
not be an economy. Consider, for example, the case where these
five lamps are of the 60-watt tungsten type, and that they are
turned off by the extra switch on an average of one-half an hour
per day while the others are needed, or vice versa. In a year's
time, the energy saved at 1 cent per kilowatt-hour, will amount to
perhaps 50 cents. At this rate it will require ten years for the
energy saved to pay for the first cost of the extra switch. This
would not be considered a distinct economy. If, however, the
energy cost be greater, and more nearly the average under actual
conditions, or if the number of hours per day during which a
portion only of the lamps will not be used, be greater, then these
values will be correspondingly modified.
Locating Switches and Controls. — In locating switches or con-
trols in factory and mill aisles, care should be exercised to ar-
range them systematically, that is, on columns situated on the
same side of the aisle and on the same relative side of each
column. This plan materially simplifies the finding of switches
or controls, by those responsible for turning on and off the lamps,
and is particularly important where a given floor space is illumin-
ated by a large number of small or medium sized lamps distri-
buted uniformly over the ceiling area, a feature which is usually
accompanied by the use of a relatively large number of switches
or controls.
Section X. Systematic Procedure Should be followed in Chang-
ing a Poor Lighting System Over to an Improved Arrangement. —
When undertaking the change from an old to a new lighting
system, the various forms of illumination which are adapted to
factory and mill spaces should be studied, and an investigation
made of the various types of gas and electric lamps on the market
which are available for the purpose.
Time should be allowed for a study of the given locations to
be lighted ; for preparing the plans of procedure in the installation
of the gas or electric lamps and auxiliaries ; and for customary
delays in the receipt of the necessary supplies and accessories to
the work in hand. Altogether, therefore, work of this kind re-
quires considerable time for its completion.
CODE OF LIGHTING 63 1
Using the Shop Force. — In large factories or mills, a wiring
or gas fitting force is sometimes a part of the maintenance divi-
sion. The work of the wiremen or fitters is likely to be heaviest
in the winter due to the dark days. Where this condition exists,
there is all the more reason to apportion out new work so as to
accomplish it during the months of least wiring and piping repair
activity, and further, at that time of the year when employees will
be comparatively unaffected by the disturbances usually asso-
ciated with a change from an old to a new lighting system through
possible irregularities in the illumination service while the wire-
men or fitters are at work.
Distribution of Expense. — Another feature different from the
foregoing viewpoint, is in the distribution of the installation cost
over a relatively long interval. If, for example, the system is
desired for the approaching winter, the complete wiring or piping
plans may be drawn up and blocked out into three, four or even
more sections, thus spreading the expense over as many months.
Yearly Appropriation. — In some shops a given appropriation
may be allotted each year for building equipment. From the
standpoint of finance plans, it may thus be desirable to distribute
outlays of this nature over the year, lather than to concentrate
them at any one time. An important consideration in this method
of installing lamps, however, is to prepare in as far as possible the
complete plans in advance, at least as regards given factory or
null sections, so as to insure a uniform and symmetrical installa-
tion as a whole when the component parts are finished.
Section XI. Reflectors and Their Effect on Efficiency. A re-
flector or shade is used in conjunction with a lamp for the pur-
pose of reducing the glare otherwise caused by looking directly
into the bare lamp, as well as for the purpose of redirecting the
light most effectively to the work.
Reflectors and shades are now obtainable so designed as to be
specially adapted to give sizes and types of the smaller and med-
ium sized line of lamps, and hence care should be used to be sure
that both reflectors and lamps are of the correct size in their
relation to each other. This is of the utmost importance in se-
curing uniform illumination for a given spacing distance and
mounting height of the lamps. For a certain ratio between the
632 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
spacing and the height of the lamps, a reflector can nearly always
be selected which will furnish uniform illumination over the
working surface. (These remarks concerning reflectors apply
particularly to lamps of the tungsten type and to small gas units.)
Function of Reflector. — Owing to the direction of the light
from the lamp, nearly all types of lamps, in addition to the down-
ward light, furnish some rays which go upwards and away in
other directions from the objects to be illuminated, and are there-
fore relatively not useful. Furthermore, a bright source in the
field of vision causes an involuntary contraction of the pupil of
the eye, which is equivalent to a decrease in illumination in so
far as the eye is concerned. Hence, while reflectors or shades
may at first seem to reduce the amount of light in the upper part
of the room, their use actually increases the amount of light in a
downward useful direction, and improves the "seeing" due to the
better conditions which surround the eyes. The economic func-
tion of the reflector, as contrasted with the easier conditions it
affords the eyes, is to intercept the otherwise useless or compara-
tively useless rays which do not ordinarily reach the wrork, and
to reflect them in a useful direction. In performing this function,
there is a choice through the design of the reflector, in the manner
of distributing the light so as to make the illumination on the
floor space uniform with certain spacing distances and mounting
heights as previously mentioned.
Avoiding Dark Spots. — With the use of lamps for which a
large variety or reflectors is available, the proper reflector should
therefore be chosen so as to give the desired distribution of light.
In other cases, as in the use of the gas or electric arc lamps,
where the globe or reflector is usually a fixed part of the lamp,
care must be exercised to space the lamps at sufficiently close
intervals to insure uniformity of the illumination, that is, a free-
dom from the relatively dark spaces which exist between lamps
when spaced too far apart.
Light Interiors. — With a light ceiling, the reflection of that
part of the light which passes through a glass reflector to the
ceiling, and which is added to the light thrown downward from
the under surface of the reflector, is a factor in building up the
intensity of the illumination on the working surface. Great
CODE OF LIGHTING 633
importance is therefore attached to light interior colors, especially
on ceilings and the upper portions of walls, both in reinforcing
the direct illumination, and in giving diffusion, zvhich in turn
adds to the amount of light received on the side of a piece of
work. It shoidd also be stated that the intensity of the light from
bare overhead lamps when measured on the working surface may
be increased by as much as 60 per cent, through the use of effi-
cient reflectors. This is due to the utilization of the horizontal
rays of light as previously stated, which predominate in the bare
lamp, whereas the most effective light in factory and mill work
is apt to be that which is directed downward.
Glass and Metal Reflectors Compared. — The question is some-
times raised as to the use of glass reflectors in connection with
lamps for factory and mill lighting. This question is largely
one of economy and maintenance, and it may be answered either
in an off hand way or on a basis of practical experience with both
types.
In large installations of small units there has been an effort
to establish the merits of glass and of metal reflectors, by equipp-
ing lamps in adjacent bays with glass reflectors in one case and
with metal reflectors in the other. It has been found almost
invariably that if the choice is left to the workmen and superin-
tendents, glass reflectors will be given preference over metal,
mainly on account of the added cheerfulness they produce. If,
therefore, the first cost and maintenance expense of the glass
reflectors in practically the same as with metal, then glass may be
employed to advantage.
Reflector Efficiency.— Class reflectors on the market are cap-
able of producing an amount of illumination equal and even
greater in some cases than that produced by the best metal re-
flectors, and even if the first cost is somewhat higher, the added
advantage of glass as opposed to metal is usually sufficient to
make the small difference in cost a negligible item. This factor
is all the more noticeable when one considers that the reflector
itself is a small part of the total cost connected with the wiring
or piping of the lamp and its reflector.
Pierced metal reflectors are also available. These are designed
with small openings at the upper portion of the metal so that
634 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
the reflector may give the same distribution characteristics as a
given glass reflector, thus affording a suitable metal reflector for
use where glass may be objectionable. Some of the advantages
of the pierced metal reflector are that it is unbreakable and that
accumulations of dust on the outer surface do not decrease the
efficiency. It is also true that the light which passes through the
openings in this reflector to the ceiling cannot be diminished by
dust on the outer surface as in the case of glass reflectors. (This
type of reflector is shown in Fig. 8 under the main line shafting.)
Reflector Maintenance. — Regarding the maintenance of glass
reflectors under rough factory and mill conditions, it may be
stated that glass reflectors are used quite widely with almost a
negligible increase due to breakage. Thus, out of the total main-
tenance cost in one representative installation, it was found that
the charges were proportioned as follows :
Renewals, cost of lamps (tungsten) 75 per cent.
Renewals, broken glass reflectors 3 per cent.
Labor, making renewals and changing reflectors
for washing 16 per cent.
Labor, reflector washing 2 per cent.
Additional indirect charges 4 per cent.
Total 100 per cent.
Points to Consider. — Reflectors will not be classified here from
the commercial standpoint, but the following items should be
given consideration in the selection of the type of reflector for
factory or mill use :
1. Utilization efficiency: how much does the reflector contri-
bute to the effective illumination on the work ?
2. The effect in reducing glare.
3. Natural deterioration with age through accumulations of
dust and dirt.
4. Ease in handling and uniformity of manufacture.
5. Physical strength and the absence of projections which may
increase the breakage in case of glass reflectors.
A study of the various reflectors on the market with the aid
of these items as a basis, will determine what reflectors are best
adapted to given conditions. Regarding the third item in the
foregoing list, it may be stated that under comparative tests in
CODE OF LIGHTING 635
service, the accumulations of dust and dirt on glass reflectors
do not seem to be any greater than the coating of dirt which ac-
cumulates on the inside of a metal reflector in the same length
of time.
Section XII. Side Light Important in Some Factory and Mill
Operations. — It has been customary in many cases to measure the
effectiveness of illumination in terms of the vertically downward
component of the light. This method has ignored the value of
side components in relation to vertical surfaces and openings in
the side of the work. It is sometimes more necessary to light
the side of the machine or the side of a piece of work than the
horizontal surface. If, then, in designing a factory or mill light-
ing system, the prime object is the production of the greatest
amount of downward illumination, it may happen that the side
component is so small that the sides of machinery or of work are
inadequately lighted.
Tzvo Ways to Secure Side Light. — Experience indicates that
there are two general ways in which to secure adequate side
lighting. One of these methods is to lower the lamps, and the
other is to use broader distributing reflectors than are called for
by the rules which consider uniformity of the downward illumin-
ation only. Side walls or other reflecting surfaces will modify
the results. Thus, after the determination of a certain type of
reflector for producing uniform vertically downward illumina-
tion, it may be found that more side light is necessary, and this
extra side component may, as stated, usually be secured by se-
lecting a somewhat more distributing reflector. Broader distri-
buting reflectors are apt to result in less downward illumination
and will sometimes call for larger lamps than found necessary by
preliminary calculations.
Practical Case. — As an illustration, in a certain lighting system
a vertically downward intensity of about 3 foot-candles was
deemed sufficient for the work involved. Measurements and
observations showed that the side light was insufficient. In this
particular installation it was found necessary to produce a verti-
cally downward intensity of about 5 foot-candles on the average
in order to secure an intensity of about 2 foot-candles on the side
of the work, and also to use a somewhat broader distributing re-
3
636 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
flector than at first chosen. Two foot-candles on the sides of the
work were sufficient in this case where bench work and work in
the vise on small machine parts were conducted.
Keeping the Lamps High. — It is recommended that the lamps
be mounted near the ceiling in all reasonable cases where side
light is necessary, and that the side light be increased, not by low-
ering the lamps, but through the medium of broader distributing
reflectors and larger lamps, if required. This attitude is taken
on account of the glare which results when lamps are mounted
too close to the work, a feature most noticeable in the absence of
a reflector or where glass reflectors are used.
Section XIII. Maintenance. — The importance of system in the
upkeep of natural and artificial lighting equipment may not ap-
peal to every reader at the outset, but a consideration of the
points involved will indicate that neglect of such work is apt to
result in excessive losses of otherwise useful light.
Windows. — Factory and mill windows become covered in time
with dirt, and produce greatly decreased values of natural light
in consequence. These losses may easily be great enough to
affect the workmen seriously, and to necessitate the use of arti-
ficial light at times when otherwise it would not be required.
Dark surroudings also increase the likelihood of accidents. Regu-
lar window cleaning should therefore be a part of the routine of
every factory and mill building or group of buildings.
Lamps. — Carbon filament, mercury-vapor, gas mantle and
tungsten lamps burn out or break, globes and reflectors become
soiled, and the various other items of deterioration take place so
gradually that in many cases they are given no special concern
in the practical economy of the shop. Moreover, it is hardly
necessary to mention the fact that often lighting systems are al-
lowed to deteriorate to an extreme point and nothing is done un-
less complaints come in from employees after the lighting facili-
ties here and there throughout the shop have become so poor that
work has to be discontinued temporarily. The losses of time
from such circumstances, when added up throughout a year, are
more than likely to exceed the expense of systematic attention to
such maintenance items in advance.
Overhead System. — Furthermore, with modern methods where
CODE OF LIGHTING
637
the lamps are usually mounted overhead rather than close to each
machine, the importance of relieving the workmen from any
care of the lamps and placing it in the hands of a maintenance
department is even greater than has been the case in the past par-
ticularly in large plants. To indicate the wisdom of a daily re-
newal of electric lamps, Fig. 24 has been worked up from the
experiences in one large factory. In this factory all burned-out
lamps are renewed each day except Saturday and Sunday, these
renewals being based on a daily inspection of every lamp to as-
certain whether or not it is in working condition.
Lamp Renewals. — A reference to the diagram shows that the
renewals are considerably greater on Monday than on any other
day of the week, this increase being due to renewals not given at-
0
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hj
3
2
SUN MON. TUES. WED THURS. FRI SAT. SUN.
Fig. 24. — Fluctuations in daily lamp renewals.
tention on the two preceding days. Obviously, therefore, a con-
tinued neglect of the inspection and renewal of these lamps would
soon result not only in inferior lighting conditions, but to large
losses of time for the employees, not to speak of the annoyance
involved.
Reflector Cleaning. — The serious loss of light when globes and
reflectors are allowed to go for long periods without cleaning, is
shown in Fig. 25. This set of curves resulted from a test on a
glass reflector used with a tungsten lamp. The one curve shows
the value of the light given by the lamp at different angles when
the lamp and reflector are clean, while the smaller curve shows
the enormous reduction of light after the lamp and reflector has
been in service for about four months without being cleaned.
638 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
In this paricular case, which is a typical one, the loss of light
at the end of the four month interval, amounted to about 50 per
cent. The cost of electrical energy in this shop was such that the
loss of light during the four months amounted to about 12 cents,
while the total cost of taking down, washing and replacing this
reflector amounted to about 3 cents. The economy of a fairly
frequent attention to cleaning of such reflectors is at once ap-
parent, even if the improved condition of the light in itself be
ignored.
The examples just given, in the one case associated with the
renewals of the lamps, in the other with the washing of the re-
flectors, will serve to illustrate the class of upkeep problems which
Fig. 25. — Curves showing serious losses of light from a tungsten lamp and its reflector due
to accumulations of dirt. This is a condition applicable to all types of lamps, as other
illuminants suffer corresponding losses from dirt accumulations.
are involved in shop lighting. The most forcible emphasis is ap-
plicable to the idea that system may properly be called a first step
towards success in this line of maintenance work.
A Method of Inspection and Maintenance. — In one large fac-
tory a regularly developed method of inspection and renewals is
employed. As an example, the method as applied to several
thousand tungsten lamps, which are in service in the various
buildings, will be described. All the lamps are inspected once
per day, except Saturday and Sunday. A regular route is
followed by the inspector, and all burned out lamps, broken
switches, loose fuses, and similar items are noted. Careful ob-
servation is also made of reflectors which appear to need washing
and any other points which might affect the efficiency of the
(.3S
Fig. 2b. — Very poor lighting in a worsted goods factory. The wiring is badly arranged, the
contrasts between light and dark portions of the room are excessive, and in some cases the
wrong size of lamp is used in a given reflector. The system is unsightly and represents
bad practise. Compare with Fig. 27.
Hig. 27.- Worsted mill with localized general illumination. This is an example of excellent
illumination with tungsten lamps and metal reflectors. Note the reflection from the goods
to the ceiling. Compare with Fig. 26.
Fig. 28. — Very poor arrangement of arc lamps. The lamps are mounted to one side of
aisle over line shafting. Very little light reaches the machinery to the right. Com-
pare with Fig. 29.
Fig. 29. — Well planed system of arc lighting. The lamps are high and above the
ordinary line of vision. Compare with Fig. 28.
CODE OF LIGHTING 639
system, after which a report is made up about noon and promptly
sent to the maintenance department to permit all renewals and
repairs to be made before night. In this manner the lamps are
well maintained from day to day.
Marking Columns. — To facilitate this renewal work, it has been
found advantageous to mark all columns through this shop. The
inspector is thus enabled to indicate clearly the location of each
burned out lamp and the renewal man to locate it without delay.
It is helpful now and then in like manner to have the inspector
note the unnecessary lamps found burning when artificial light
is not required. If lamps are found burning at such times, a note
sent to the head of the department calling attention to the matter
is usually sufficient to remedy the difficulty.
Noting Soiled Reflectors. — As a check on a regular cleaning
schedule, the inspector should note all reflectors in need of clean-
ing. The frequency of each cleaning will depend on the rate of
deterioration due to the settlement of dirt on the surface of the
glass or metal and also on the surface of lamps, and the fact
should be kept in mind that the amount of dirt on a reflector is
nearly always deceptive, that is, reflectors which have suffered
a large deterioration in efficiency due to dirt often appear fairly
clean, and for this reason it is best to increase the frequency
of cleaning somewhat over that which seems sufficient from ob-
servation, particularly in view of the fact that tests indicate large
reductions of light from apparently small accumulations of dust
and dirt.
A Method of Washing. — In the factory just referred to, all
reflectors are removed to a central washing point. Where the
number of reflectors to be hauled is large, a truck is used. Often,
however, where only a small number of reflectors is to be trans-
ported, small hand racks, devised for the purpose, are employed.
When an installation is in need of washing, the scheme is to haul
sufficient clean reflectors to the location in question. The soiled
reflectors are then taken down and clean ones immediately put
into place, after which the soiled reflectors are removed to the
central washing point, washed and put into stock for the next
location.
64O TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
Section XIV. Expert Assistance Suggested. — The advantages of
securing expert assistance in dealing with illumination is strongly
emphasized. The points which come up for solution are complex
and require, in many cases, the judgment of one who has had
wide experience in the lighting field. In particular, anyone who
undertakes to adopt any part or all of these suggestions will do
well to secure the co-operation of a lighting expert capable of
interpreting the legislative articles and of advising in a con-
structive manner.
Section XV. Other Features of Eye Protection. — Care is urged
on the part of those responsible for the health and welfare of
employees to see that adequate eye protection is afforded in all
operations which are apt to cause injury to eyesight, if such
protection is neglected. As typical of such other causes of danger
to eyesight, arc welding may be mentioned, where the operator,
according to accepted practise, must wear a helmet serving as an
eye shield as well as a shield for the face and head in general.
Protective glasses for this purpose should not be judged as to
their protective properties by mere visual inspection. They
should, hoivever, be analysed for their spectral transmission of
invisible radiation. Protective measures should also be taken to
prevent on-lookers from being unduly exposed to such eye
dangers, by enclosing the welding operations with suitable parti-
tions. These general remarks apply with equal force from the
standpoint of those handling the operations to such other cases
as the testing of arc lamps, inspection of hot metal and similar
cases.
Section XVI. Auxiliary Systems for Safety. — The auxiliary
system of lighting called for in Article XI of the Code, is a safety
first precaution which is insisted upon in a large proportion of
the 1,200 buildings coming under the control of the Bureau of
Water Supply, Gas and Electricity in New York City, particu-
larly such buildings as are occupied by large numbers of people.
The same precaution is now observed by the Bell Telephone Com-
pany's offices fairly generally throughout the country, also by a
large number of private manufacturers and by local ordinances
compelling all types of amusement places to take this precaution.
CODE OF LIGHTING 64I
Section XVII. Good and Bad Lighting Compared. — In order to
give an idea of good and bad lighting, Figs. 13, 14, 26, 27, 28 and
29 are shown. These illustrations indicate the use of various
types of lamps and a reference to the captions under the illustra-
tions will bring out the weak points of the poorly lighted spaces,
as well as the points of excellence in those cases which are de-
signed in conformity with good illumination practise.
642 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
1915 REPORT OF THE COMMITTEE ON NOMENCLA-
TURE AND STANDARDS OF THE ILLUMIN-
ATING ENGINEERING SOCIETY.*
DEFINITIONS.
Luminous flux is radiant power evaluated according to its
capacity to produce the sensation of light.
The stimulus coefficient KA for radiation of a particular wav
length is the ratio of the luminous flux to the radiant power pro-
ducing it.
The mean value of the stimulus coefficient, Km, over any range
of wave-lengths, or for the whole visible spectrum of any source,
is the ratio of the total luminous flux (in lumens) to the total
radiant power (in ergs per second, but more commonly in watts).
The luminous intensity of a point source of light is the solid
angular density of the luminous flux emitted by the source in
the direction considered; or it is the flux per unit solid angle
from that source.
Defining equation :
Let I be the intensity for the flux and w the solid angle.
Then I = *
aw
or, if the intensity is uniform,
CO
Illumination, on a surface, is the luminous flux-density over
that surface, or the flux per unit of intercepting area.
Defining equation :
Let E be the illumination and S the area of the intercepting
surface.
Then E = d
or, when uniform,
dS'
K-^"'
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
191 5 REPORT ON NOMENCLATURE AND STANDARDS 643
Candle — the unit of luminous intensity maintained by the
national laboratories of France, Great Britain, and the United
States.1
Candlepower — luminous intensity expressed in candles.
Lumen — the unit of luminous flux, equal to the flux emitted in
a unit solid angle (steradian) by a point source of one candle-
power.2
Lux— a unit of illumination equal to one lumen per square
meter. The C. G. S. unit of illumination is one lumen per square
centimeter. For this unit Blondel has proposed the name "Phot."
One millilumen per square centimeter (milliphot) is a practical
derivative of the C. G. S. system. One foot-candle is one lumen
per square foot and is equal to 1.0764 milliphots.
Exposure — the product of an illumination by the time. Blondel
has proposed the name "phot-second" for the unit of exposure
in the C. G. S. system.
Specific luminous radiation — the luminous flux-density emitted
by a surface, or the flux emitted per unit of emissive area. It is
expressed in lumens per square centimeter.
Defining equation :
Let E' be the specific luminous radiation.
Then, for surfaces obeying Lambert's cosine law of emission.
E' = ^0.
Brightness, b, of an element of a luminous surface from a given
position, may be expressed in terms of the luminous intensity per
unit area of the surface projected on a plane perpendicular to
the line of sight, and including only a surface of dimensions
negligibly small in comparison with the distance to the observer.
It is measured in candles per square centimeter of the projected
area.
Defining equation:
Let 6 be the angle between the normal to the surface and the
line of sight.
Then
dl_
~~ dS cos &
1 This unit, which is used also by many other countries, is frequently referred to as
the international candle.
2 A uniform source of one candle emits 4 n lumens.
644 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
Normal brightness, b0, of an element of a surface (sometimes
called specific luminous intensity) is the brightness taken in a
direction normal to the surface.3
Denning equation:
or, when uniform, 60 — — .
Brightness may also be expressed in terms of the specific
luminous radiation of an ideal surface of perfect diffusing qual-
ities, i. e., one obeying Lambert's cosine law.
Lambert — the C. G. S. unit of brightness, the brightness of a
perfectly diffusing surface radiating or reflecting one lumen per
square centimeter. This is equivalent to the brightness of a per-
fectly diffusing surface having a coefficient of reflection equal
to unity and illuminated by one phot. For most purposes, the
millilambert (0.001 lambert) is the preferable practical unit.
A perfectly diffusing surface emitting one lumen per square
foot will have a brightness of 1.076 millilamberts.
Brightness expressed in candles per square centimeter may be
reduced to lamberts by multiplying by it = 3.14.
Brightness expressed in candles per square inch may be re-
duced to foot-candle brightness by multiplying by the factor
144 7T = 452.
Brightness expressed in candles per square inch may be re-
duced to lamberts by multiplying by 71-/6.45 — 0.4868.
In practise, no surface obeys exactly Lambert's cosine law of
emission; hence the brightness of a surface in Lamberts is, in
general, not numerically equal to its specific luminous radiation
in lumens per square centimeter.
Defining equations :
L =
d$
or, when uniform,
*-f
3 In practise, the brightness b of a luminous surface or element thereof is observed,
and not the normal brightness ba. For surfaces for which the cosine law of emission
holds, the quantities b and ba are equal.
191 5 REPORT ON NOMENCLATURE AND STANDARDS 645
Coefficient of reflection — the ratio of the total luminous flux
reflected by a surface to the total luminous flux incident upon it.
It is a simple numeric. The reflection from a surface may be
regular, diffuse or mixed. In perfect regular reflection, all of
the flux is reflected from the surface at an angle of reflection
equal to the angle of incidence. In perfect diffuse reflection the
flux is reflected from the surface in all directions in accordance
with Lambert's cosine law. In most practical cases there is a
superposition of regular and diffuse reflection.
Coefficient of regular reflection is the ratio of the luminous
flux reflected regularly to the total incident flux.
Coefficient of diffuse reflection is the ratio of the luminous
flux reflected diffusely to the total incident flux.
Defining equation:
Let m be the coefficient of reflection (regular or diffuse).
Then, for any given portion of the surface,
E'
m = — .
E
Lamp — a generic term for an artificial source of light.
Primary luminous standard — a recognized standard luminous
source reproducible from specifications.
Representative luminous standard — a standard of luminous
intensity adopted as the authoritative custodian of the accepted
value of the unit.
Reference standard — a standard calibrated in terms of the unit
from either a primary or representative standard and used for
the calibration of working standards.
Working standard — any standardized luminous source for daily
use in photometry.
Comparison lamp — a lamp of constant but not necessarily
known candlepower against which a working standard and test
lamps are successively compared in a photometer.
Test lamp, in a photometer — a lamp to be tested.
Performance curve — a curve representing the behavior of a
lamp in any particular (candlepower, consumption, etc.) at differ-
ent periods during its life.
Characteristic curve — a curve expressing a relation between
646 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
two variable properties of a luminous source, as candlepower
and volts, candlepower and rate of fuel consumption, etc.
Horizontal distribution curve — a polar curve representing the
luminous intensity of a lamp, or lighting unit, in a plane perpen-
dicular to the axis of the unit, and with the unit at the origin.
Vertical distribution curve — a polar curve representing the
luminous intensity of a lamp, or lighting unit, in a plane passing
through the axis of the unit and with the unit at the origin.
Unless otherwise specified, a vertical distribution curve is as-
sumed to be an average vertical distribution curve, such as may
in many cases be obtained by rotating the unit about its axis,
and measuring the average intensities at the different elevations.
It is recommended that in vertical distribution curves, angles of
elevation shall be counted positively from the nadir as zero, to
the zenith as 1800. In the case of incandescent lamps, it is
assumed that the vertical distribution curve is taken with the
tip downward.
Mean horizontal candlepower of a lamp — the average candle-
power in the horizontal plane passing through the luminous center
of the lamp.
It is here assumed that the lamp (or other light source) is
mounted in the usual manner, or, as in the case of an incan-
descent lamp, with its axis of symmetry vertical.
Mean spherical candlepower of a lamp — the average candle-
power of a lamp in all directions in space. It is equal to the
total luminous flux of the lamp in lumens divided by 477-.
Mean hemispherical candlepower of a lamp (upper or lower) —
the average candlepower of a lamp in the hemisphere considered.
It is equal to the total luminous flux emitted by the lamp in that
hemisphere divided by 2-n.
Mean zonal candlepower of a lamp — the average candlepower
of a lamp over the given zone. It is equal to the total luminous
flux emitted by the lamp in that zone divided by the solid angle
of the zone.
Spherical reduction factor of a lamp — the ratio of the mean
spherical to the mean horizontal candlepower of the lamp.4
4 In the case of a uniform point-source, this factor would be unity, and for a straight
cylindrical filament obeying the cosine law it would be jt/4.
191 5 REPORT ON NOMENCLATURE AND STANDARDS 647
Photometric tests in which the results are stated in candlepower
should be made at such a distance from the source of light that
the latter may be regarded as practically a point. Where tests
are made in the measurement of lamps with reflectors, the results
should always be given as "apparent candlepower" at the distance
employed, which distance should always be specifically stated.
The output of all illuminants should be expressed in lumens.
Illuminants should be rated upon a lumen basis instead of a
candlepower basis.
The specific output of electric lamps should be stated in terms
of lumens per watt and the specific output of illuminants depend-
ing upon combustion should be stated in lumens per British ther-
mal unit per hour. The use of the term "efficiency" in this con-
nection should be discouraged.
When auxiliary devices are necessarily employed in circuit
with a lamp, the input should be taken to include both that in
the lamp and that in the auxiliary devices. For example, the
watts lost in the ballast resistance of an arc lamp are properly
chargeable to the lamp.
The specific consumption of an electric lamp is its watt con-
sumption per lumen. "Watts per candle" is a term used com-
mercially in connection with electric incandescent lamps, and
denotes watts per mean horizontal candlepower.
Life tests — Electric incandescent lamps of a given type may be
assumed to operate under comparable conditions only when their
lumens per watt consumed are the same. Life test results, in
order to be compared must be either conducted under, or reduced
to, comparable conditions of operation.
In comparing different luminous sources, not only should their
candlepower be compared, but also their relative form, bright-
ness, distribution of illumination and character of light.
Lamp Accessories. — A reflector is an appliance the chief use of
which is to redirect the luminous flux of a lamp in a desired
direction or directions.
A shade is an appliance the chief use of which is to diminish
or to interrupt the flux of a lamp in certain directions where such
flux is not desirable. The function of a shade is commonly com-
bined with that of a reflector.
648 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
A globe is an enclosing- appliance of clear or diffusing material
the chief use of which is either to protect the lamp or to diffuse
its light.
Photojmetric Units and Abbreviations.
Photometric
quantity
Luminous flux
Luminous intensity
Name of
unit
Lumen
Candle
Abbreviations, symbols
and defining eqations
*
dF
d*
du ' du>
3-
Illumination
Phot, foot-candles, lux
E =
dF I
dS — r2
4-
Exposure
Phot-second
Apparent candles
El
per sq. cm.
b —
dl
5-
Brightness
Apparent candles
per sq. in.
dS cos 6
Lambert
L =
dF
~ds
6.
Normal bright:
aess
Candles per sq. cm.
Candles per sq. in.
h =
dl
~~ dS
7-
Specific luminous
radiation
Lumens per sq. cm.
Lumens per sq. in.
E'=
: ir£0, 0'
8.
Coefficient of
flection
re-
—
m =
E/
E
9. Mean spherical
candlepower
10. Mean lower hemi-
spherical candle-
power
11. Mean upper hemi-
spherical candle-
power
12. Mean zonal candle-
power
13. 1 lumen is emitted by 0.07958 spherical cp.
14. 1 spherical candlepower emits 12.57 lumens.
15. 1 lux = 1 lumen incident per square meter ;
phot.
16. 1 phot = 1 lumen incident per sq. cm. = 10,000 lux = 1000 milliphot.
17. 1 milliphot = 0.001 phot = 0.929 foot-candle.
18. 1 foot-candle = 1 lumen incident per square foot = 1.076 milliphot
10.76 lux.
19. 1 lambert = 1 lumen emitted per square centimeter.*
20. 1 millilambert = 0.001 lambert.
scp
lcp
ucp
zcp
0.0001 phot = 0.1 milli-
191 5 REPORT ON NOMENCLATURE AND STANDARDS 649
21. i lumen, emitted, per square foot* = 1.076 millilambert.
22. 1 millilambert = 0.929 lumen, emitted, per square foot.*
23. 1 lambert = 0.3183 candle per sq. cm. = 2.054 candles per sq. in.
24. 1 candle per sq. cm. = 3.1416 lamberts.
25. 1 candle per sq. in. — 0.4868 lamberts = 486.8 millilamberts.
SYMBOLS.
In view of the fact that the symbols heretofore proposed by
this committee conflict in some cases with symbols adopted for
electric units by the International Electrotechnical Commission,
it is proposed that where the possibility of any confusion exists
in the use of electrical and photometrical symbols, an alternative
system of symbols for photometrical quantities should be em-
ployed. These should be derived exclusively from the Greek
alphabet, for instance :
Luminous intensity T
Luminous flux &
Illumination /3.
DISCUSSION.
Mr. F. A. Benford : I note in the text that the words "candle"
and "candlepower" are used interchangeably. I wonder if Dr.
Sharp will tell us if this Society has ever taken a stand as to
preference in the use of the word "candle" or "candlepower?"
Mr. R. ff. Pierce : I should like to call attention to the possi-
bility that the rating of lamps in the terms set forth on the sixth
page might introduce some confusion commercially. It is recom-
mended that the specific output of illuminants depending on com-
bustion shall be stated in British thermal units per hour. In
actual practise in the case of illuminants operated by gas, it has
been demonstrated that the light output is practically independent
of the calorific value of the gas. As the adoption of such a
system of rating might conflict with or confuse commercial rat-
ings, I should urge that it be offered in such a way as to make
impossible any such confusion ; it is not a practical way of rating
commercially lamps of that type.
Mr. P. S. Millar: On the second page the committee defines
the word "lux." I should like to ask if the committee wishes us
to use that unit of illumination? It is used in Germany, based
upon the Hefner. It is proposed here in connection with candle. If
* Perfect diffusion assumed.
650 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
the committee does not wish us to use the word "lux" in our work,
I think it should not be featured so prominently in the report.
Most of the paragraph under lux is devoted to a discussion of the
phot. If the committee wishes us to use the phot, I think it should
be featured; it is given rather incidentally at the present time.
Mr. J. R. Cravath : I believe I am correct that the new
unit of brightness called the lambert is the first one to be dis-
tinctly originated within our Society through its Committee. I
hope those who are working in brightness values will promptly
adopt this new unit in publications relating to brightness.
Dr. C. H. Sharp : Mr. President, the first question was, "Has
the Society said anything on the subject of candle versus candle-
power?" At the top of the second page of the report you will
find this :
Candle, the unit of luminous intensity maintained by the national
laboratories of France, Great Britain and the United States.
Candlepower, luminous intensity expressed in candles.
Mr. Pierce made some statement regarding the luminous output
of gas lamps. He raised an objection to the rating of them in
terms of British thermal units. That is a question the merits of
which I am unable to go into. I would say, however, that the
proposition which came to the committee first was that gas lamps
should be rated in lumens per cubic foot per hour, but the prom-
inent gas engineers on the committee preferred a rating in terms
of lumens per British thermal units per hour, because the lumens
were proportional to the British thermal units of the gas.
Mr. Millar has raised the question of the prominent featuring
of the term "lux." I think his criticism is pretty well taken. My
understanding of it has been that we have put in this tentative
proposal of the word "phot," as made by Blondel, largely with
the idea that it would form a basis eventually for a real, inter-
national unit of illumination. Now, the lux is unfortunately a
kind of a bipartisan unit; so that perhaps the best thing under
present conditions would be for us to drop lux entirely and to
come out squarely and say we propose to use the phot and milli-
phot. The milliphot has a considerable advantage in being only
7 per cent, removed from the foot-candle, and we would under-
stand illumination values in milliphots very readily on this ac-
count.
chapman: office lighting 651
ARTIFICIAL LIGHTING OF TYPICAL OFFICES IN
STATE, WAR, AND NAVY DEPART-
MENT BUILDING.*
BY W. F. CHAPMAN.
Synopsis: This paper describes the old and new lighting conditions
in the State, War, and Navy Department Building which was constructed
in 1871-1886. Especial attention is given to the present-day lighting
requirements in the building and the new system of general illumination
by which they have been satisfactorily met. The colors used on the walls
and ceilings of the rooms with the view to obtaining the maximum effi-
ciency of tungsten filament incandescent lamps of about 1 watt per candle-
power are also discussed ; and it is shown that in the new system the
energy consumption is 1 watt per square foot of floor space.
The State, War, and Navy Department Building at Washing-
ton, D. C, which was constructed during the period of 1871 to
1886, at a cost of upwards of $10,000,000, and whose combined
floor space is upwards of ten acres, has since its completion been
referred to as the largest and finest office building in the world.
The architectural arrangement of its rooms for natural light and
ventilation, as well as for convenience of access, is unexcelled to-
day; but naturally enough the artificial lighting system originally
installed, consisting at first of gas burners attached to large
ornamental, solid brass chandeliers, and later a crude combina-
tion of both gas and electricity, was soon outstripped by the rapid
developments in illuminating engineering.
There was one four-burner gas chandelier installed in the
center of each room containing 400 square feet of floor space,
which in general is the uniform size of all the office rooms. From
the standpoint of beauty and uniformity this arrangement of the
gas fixtures was splendid, but its impracticability was developed
as soon as the rooms were occupied, and it was found on cloudy
days, when artificial light was indispensable, that these fixtures
furnished sufficient light only for those desks and files which
were located directly under them and for a short radius from
the center of the room. The great number of desks and files
required by each of the three departments especially in rooms
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, I9I 5-
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
4
652 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
occupied by the large clerical forces made necessary the placing
of many desks and files at convenient intervals in all parts of the
room. In the natural order of things the larger files, which were
put in in rapidly increasing numbers, many of them extending
from the floor to an 18 foot (548 m.) ceiling, were placed against
the partition and the interior walls, where the light faded into
insufficiency for practical purposes. Many desks and files were
of necessity placed beyond the zone of sufficient illumination, so
that on dark days the efficiency of the employees was consider-
ably lowered, while some of the employees suffered from im-
paired eyesight.
To overcome these difficulties an electric lighting system was
added throughout the building in 1887 and 1888; the arrangement
of the lamps was governed by the location of the gas lights and
desks and files, and therefore without any rule of uniformity.
This installation, though void of beauty, proved to be practical,
at least, for the time being; but as the business of the departments
grew, increasing the personnel, desks, files, and such office appli-
ances as the typewriter, adding machine, etc., the furniture and
fixtures had to be rearranged in the rooms accordingly. Such
rearrangement meant constant rearrangement of the electric lamps
and later the installation of many desk lamps of different makes
and of a variety of styles. Two to four electricians were kept busy
most of the time making these changes and the rooms were soon
filled with unsightly wires and old style rosettes and fixtures;
the ceilings and walls were marred with plugs and broken plaster.
Some of the units were in use, and as often as not many of them
were out of service.
The desk lamp feature was particularly annoying and came to
be known in the superintendent's office as the "desk lamp
nuisance" not only in the matter of changes required by rear-
rangements of desks, etc., but because these lamps would often
appear within the working vision of persons occupying desks in
other parts of the rooms. Wires leading to them were also in
the way and these and the other lamps, including gas chandeliers,
became the lodging places for large quantities of dirt which, ex-
cept in a few instances, was never removed.
Moreover, when the original electrical installation was made,
a conically shaped metal reflector was used. These reflectors, of
CHAPMAN : OFFICE LIGHTING
653
course, prevented the rays of artificial lights from reaching the
upper sections of file cases which, in almost all instances, are in-
dexed on the outside of the box or drawer units that fill up their
framework. Some means had to be provided to afford artificial
light for these files and even the cumbersome wire-guarded port-
able lamp was furnished in many of the offices and file rooms, so
that users of the files could see well enough to do their work.
rO—
?
I CROSS-SECTION
OF CEILING ARCH
O^
9
n
1 1
LJ
n
p
■«
n CEILING OUTLETS
t] BASEBOARD OR WALL
OUTLETS
Ei JUNCTION BOX
S SWITCH
MANNER IN WHICH
CIRCUITS ARE TO BE RUN
Fig. 1. — Plan of rewiring a typical room.
It became apparent that this chaotic condition had to be over-
come by the installation of some general and uniform system of
illumination, and with this end in view the superintendent of the
building set about a careful and exhaustive study of the problem.
In this study he sought and obtained the advice of some of the
most celebrated illuminating engineers and experts of the coun-
try. He also consulted with a number of the larger manufac-
turers of modern fixtures, who furnished him with various sam-
ples representing their different styles and sizes of lighting units
which he installed and tested under different conditions. In con-
nection with the efficiency and adaptability of these units, he
654 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
studied the effects of the color of walls and ceilings on the artifi-
cial light and on the eye to determine what color scheme would
serve best for use with both natural and artificial light from the
standpoint of its being one that would harmonize with and be a
proper reflector of light, and upon the principle that such a
scheme must also afford the eye a restful relief when raised from
the routine of office duty.
Particularly on account of the frequent criticism of the ven-
tilation, especially during the winter months when doors and
windows are closed and artificial lighting is most in use, the
superintendent decided to use electric incandescent lamps
throughout.
Photometric tests were made to ascertain the quantity of light
required per square foot of floor, wall and ceiling space within
the rooms with different color combinations and different sizes
of lamps. These tests covered a period of about one year and
certain rooms were wired and refinished in this scheme to ascer-
tain its adaptability.
With the adopted scheme the walls were given a flat finish of
buff, near cream, and the ceilings a finish of ivory white. The
lighting was by means of tungsten filament incandescent lamps of
about I watt per candlepower, selected and placed uniformly so
as to give an energy consumption of I watt per square foot. The
floor area of each room was divided into squares of about 100
square feet (9.29 sq. m.) each and a bowl-frosted lamp with a
modern translucent, light opal reflector suspended over the center
of each square at a height of 9 feet (2.7 m.) above the floor.
(See Fig. 2.)
The frosted bowl prevented any direct rays of light from strik-
ing the eye through that portion of the lamp which was exposed
at the bottom of the reflector. The reflector of course served to
avoid glare from rays appearing through the clear portion of the
lamp and, being of a high quality of illuminating glass, diffused
the rays of light against the ceilings and the upper half of the
walls. The ivory white ceilings and buff walls reflected a great
portion of the upward light rays, establishing a special diffusion
at the lighting units and a general diffusion at the walls and
ceilings, particularly from the ceiling.
LS"4-
Fig. 2. — A typical small office occupied by clerks.
Fig. 3.— Standard fixtures used in building.
Fig. 4.— Seven four-unit rooms brought together by removal of partitions.
Fig. 5. — A drafting room with special spacing of fixtures.
CHAPMAN : OFFICE LIGHTING
655
The fixtures proper are of two kinds : solid brass chains in the
principal office rooms and gold colored silk, duplex No. 16
Brown and Sharpe gauge lamp cord suspended from a brass egg
and dart canopy which rests against the ceiling. Chain pull
sockets were installed for individual control of the lamps with only
chain enough to reach to within about one inch of the lower edge
of the reflector. One switch to control all four lamps in each
room was installed at a location convenient of access, usually
near the door, one attachment plug being placed adjacent to the
switch and all mounted with one brass cover flush with the wall,
30* IS* 0° 15° 30°
REFLECTOR WITH FROSTED BOWL LAMPS
Fig. 6. — Photometric distribution curve of reflector with a frosted bowl lamp.
5
104
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DISTANCE IN FEET FROM CENTER OF ROOM
Fig. 7. — Illumination on a horizontal plane 6 ft. 6 in. below two ioo-watt, bowl-frosted
tungsten lamps with reflectors spaced 10 ft. apart.
where possible. The pull switches permit the two lamps nearest
the windows to be turned off without disturbing the other two
when the latter are needed in the darker part of the room.
The accompanying drawing, Fig. I, shows how the lamps
and the circuits to them as well as fan circuits are arranged in
the rooms. Such a system of course reduces but does not elim-
inate distinct shadows, as it is readily apparent that the light re-
flected by the walls and ceiling and appearing from the respective
units cannot be strong enough to prevent an object from casting
656 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
as many shadows as there are lamps in a room, the intensity of
each shadow depending largely upon the relative position of the
object from the various lamps.
These reduced shadows have been found to be of practically no
no prejudicial consequences to any of our people except the drafts-
men, and they have not had occasion to offer any serious complaint.
It would appear to be worthy of mention here also that in his
efforts to arrive at a satisfactory system of general illumination,
the superintendent sought to approach as nearly as possible a
flat curve of illumination throughout all parts of the room, walls
and ceilings included ; and the wall and ceiling reflections in addi-
tion to the diffusion at the lamps go as far towards accomplish-
ing such a result, perhaps, as could be by the use of exposed
illuminating units.
To replace all the old objectionable special illumination with
an efficient system of general illumination throughout the build-
y 3
a
z
* ?
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p I
/
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0 I
1
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5
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3 10
Fig. 8. — Illumination on a horizontal plane, 6 ft. 6 in. below 4,100-watt, bowl-frosted tung-
sten lamps, with translucent reflectors, spaced 10 ft. apart. Curve taken on a line
through center of four-unit room, 2 ft. 6 in. above the floor, or at about the top of the
ordinary desk.
ing was the one paramount, thing to be accomplished, and it was
the determination of the superintendent that this should be done.
Many persons accustomed to the use of desk or individual drop
lamps registered vigorous protests against their being compelled
to use the general system, but once it was installed and the walls
and ceilings changed from the old dark, light-absorbing blue to
the more cheerful, light-reflecting buff and white, the value and
practicability of the change was immediately appreciated.
The work of re-illuminating the entire building, except for a
few special rooms, was commenced in November, 1914, and com-
pleted in February, 1915.
In practise so far the new scheme has produced eminently
satisfactory results, and it is believed that it will meet all ordinary
office requirements for a long time to come.
OFFICE LIGHTING 657
DISCUSSION.
Mr. W. A. Durgin : Figs. 7 and 8 show a maximum foot-
candles intensity below 3. Does this represent the "new lamp
and clean reflector" condition? With the marked increase in
lamp efficiencies it would seem that our government should em-
ploy much higher intensities not only to secure higher output
from the workers, but also to take position in the forward line
of progress.
Mr. W. E. Chapman (In reply) : Lighting conditions are
such that during the daytime there is enough natural light in most
of the rooms, except on cloudy days. It is not required that the
artificial lighting units shall supply all of the light. They are
merely auxiliary to the natural light. Persons working at night,
however, find the artificial light adequate for all general pur-
poses.
Mr. G. S. Barrows: This is a very interesting paper, but I
cannot add much to the discussion except simply to agree with
Mr. Durgin. I think we ought to be rather careful to note the
difference between new and clean lamps and the average con-
dition. Mr. Chapman's curves show a fair average condition;
that was a point that was not quite clear to me, but that has just
been explained.
Mr. W. E. Chapman : That was the condition.
Mr. G. S. Barrows: I don't understand from the paper
that there has been any attempt to install indirect or semi-indirect
lighting. I should like to know whether the architectural con-
struction is such that it is inadvisable, or why some attempt was
not made to install either of these systems.
Mr. W. E. Chapman : The reason is quite clear. We have
a condition that would permit of semi-indirect or indirect light-
ing, but it was a question of funds. We were dependent upon
the appropriation of Congress for making the improvements that
were necessary; it was impossible to get sufficient money from
Congress to make a better installation. We had, therefore, to do
the next best thing and use the system outlined in my paper.
When the wiring in the State, War and Navy Department
Building was installed in 1887 and 1888, the circuits were simply
658 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
run in wooden mouldings, which were exposed and altogether it
was a very poor and hazardous installation ; but in the new wiring
process the circuits have been run in metallic conduits in all in-
stances so that they are now thoroughly up to date throughout
the building.
DICKER AND KIRK: LIGHTING IN OFFICE BUILDINGS 659
LIGHTING IN DOWNTOWN OFFICE BUILDINGS.*
BY ALFRED O. DICKER AND JAMES J. KIRK.
Synopsis: This paper contains data in tabular form concerning elec-
tric lighting service in certain office buildings in the downtown district
of Chicago. The buildings were selected as typical examples of lighting
installations made thirty, twenty-five, twenty, fourteen and six years ago;
and one which was completed recently. Curves are given to show the
relation between watts per square foot and foot-candles for the thirty
years, and also the relation of cost per square foot per month for the
various buildings. No attempt has been made in the paper to give a
technical description of the present installations or to give recommenda-
tions for changes. The installations have been taken as they are and the
description given.
The illuminating engineer is by nature attracted to the proposed
building rather than to the older one which he passes in his every-
day walks of life. He is desirous of having the lighting in the
new building when completed typical of the best lighting practise,
and in the age of "tear-down-the-old and build-a-new" he has
found a large field. Nevertheless in the older buildings lies a
much larger field of almost untouched harvest. In these, the
older buildings, are thousands of workers toiling under lighting
conditions typical of the first installations that were made. These
lighting systems will soon be changed. They are so old now that
either the wiring will be condemned by the various inspection
departments, or else the tenants or owners will realize that for
their own mercenary benefit more and better light must be pro-
vided for their employees.
The lighting of thirty years ago is as absurd to-day as the
business policies of that period when applied to present-day
business. It is also true that antiquated lighting installations
are just as much a source of real loss as are antiquated
business systems. Proper lighting is now generally considered
an essential part of factory equipment and an essential item
in the reduction of manufacturing cost; but at present it is not
generally accepted among business men as an item in reducing
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
660 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
office costs. Data showing- the reduction of office cost are diffi-
cult to obtain, but few engineers would dispute the statement
that the working efficiency of a clerk or stenographer is reduced
25 per cent, after sundown in a poorly lighted office. This is
the period of the day when the workers are tired and is therefore
the period during which their comfort and efficiency should be
considered.
One of the objects of this paper is to show the progress of
lighting practise in downtown office buildings during the last
thirty years, by taking as examples buildings typical of the periods
during which they were built. For this purpose six buildings
were chosen as follows :
Building No. 1 built 30 years ago
2 '
' 25
3 '
1 20
4 '
' 14
5 '
' 6
In all these buildings, even the most modern, are installations
which the illuminating engineer would refuse to-day to accept as
proper lighting; but nevertheless they are considered typical for
the purpose of this paper.
It so happens that the oldest building chosen is one in which
the owners had foresight enough at the time of its construction
to wire for electricity. In the next two, in age, wiring was
omitted at the time of construction but soon thereafter it was
wired in exposed conduit or wooden moulding. In all three of
these buildings the lighting is crude both from point of construc-
tion and resulting illumination. The installation has been made
without thought or design — a drop cord installed over the desk
or table where light was required. At this period electric light
was expensive and the minimum amount was therefore utilized.
A summary of the lighting of these three buildings is of little or
no interest except as a comparative basis. The lighting is local-
ized without reflectors in many cases and where reflectors are
found a very cheap and inefficient one has been installed. The
lighting is very inadequate. The original installation was of
carbon lamps which have now been replaced by tungsten lamps,
usually of 40 and 60-watt size. Cluster fixtures as a rule pre-
vail— the most predominant type being a three or four-arm fixture
DICKER AND KIRK: LIGHTING IN OFFICE BUILDINGS 66l
suspended on a rigid stem installed approximately 6 ft. 6 in.
(1.98 m.) above floor. Wall switches were used occasionally,
but as a rule key-sockets have been utilized. The esthetic con-
siderations were not developed, but rather the lighting fixture
was considered a necessary evil and not an ornament.
The next three buildings in chronological order show somewhat
the effect of the illuminating engineer, at least it may be said
that the lighting equipment has been given some attention. The
fixtures are more efficient, more ornate, and general illumination
has been introduced. The spacing shows a decided tendency
away from localized lighting although in many of the offices,
desk lamps have had to be relied upon. Particularly in these
newer buildings the individual taste of the tenant as regards his
lighting is evident, and so there are seen suites with semi-direct
and indirect systems in all their variations.
The general building conditions are tabulated in Table I, which
will answer at a glance many of the questions which might arise
as to the details of the physical characteristics of the building and
its lighting equipment. Its only value will be for purposes of
comparison with Table II and a description of the lighting fixtures
used. A continued advancement in fixture design, the tendency
toward larger lamps and the deviation from localized lighting
toward general illumination is seen in columns 6 to 16, with the
addition in the newer buildings of semi-direct and indirect. It
would be well to add here that even in the oldest building there
exist installations of semi-direct and direct but these do not occur
in sufficient numbers to change the typical lighting system of the
building. It must be remembered that these buildings were not
selected as examples of good lighting, but rather as buildings
containing lighting installations typical of the age in which they
were built.
Table II shows the total building light and power load to-
gether with such factors as influence the cost of such service.
The connected load may be referred to Table I for reference to
the size of the building.
The load-factor1 varies from 6.34 per cent., or 1.52 hours, to
1 Load-factor, as used in this paper, may be described as follows : The ratio of
actual monthly meter consumption (Kw-h.) to continuous use of maximum demand, or
Kw-h. (consumption)
720 X Kw-h. (maximum)
662 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
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DICKER AND KIRK : LIGHTING IN OFFICE BUILDINGS 663
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664 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
17.48 per cent., or 4.2 hours use of maximum demand. The
minimum may be explained by the fact that this building is one
in which the lighting was installed after the building was com-
pleted and the installation was very inadequate. The maximum
load-factor occurs in a newspaper building of such design that
many of the lights burn of necessity most of the day.
The rates for electric service upon which is based the "average
net bill per month" is as follows : the building owner buys the
electric service for light and power either on a wholesale con-
tract, if the building is of sufficient size, or on separate contracts
for light and power. In either case in the buildings chosen for
discussion in this paper the tenants are individual customers of
the Commonwealth Edison Company. In the determination of
the item of cost, the ratio of maximum demand to connected load
is a prominent factor and for this reason it is here included.
TABLE II-A.— Comparative Lighting Data.
Age
Total building light and power
Bldg.
Connected
Per cent,
load-
factor
Av. Kw-h.
Av. max.
Av. net
bill
per month
Ratio max.
connected
load Kw.
per month
per month
load
per cent.
1
2
3
4
5
6
7
8
I
30
IOO.I08
IO.45
7,535-8
70.O
1 388.37
70
2
25
I59.2IO
6-34
7,212.9
63-3
357.52
39
3
20
380.124
7-33
20,062.7
232.4
1,008.75
61
4
14
877.823
17.48
110,486.4
424.2
2,347.20
48
5
6
I99.089
13-03
18,241.1
134-4
745-47
67
6
1
342.790
6.38
15,978.7
96.0
610.82
28
TABLE II-B.— Comparative Lighting
Data.
Elevators and Public lights
Bldg.
Elevators
Connected
load Kw.
Per cent,
load-
factor
Av. Kw-h.
per month
Av. max.
Kw.
per month
Av. net
bill
per month
Ratio of
max. to
connected
load
I
2
3
4
5
6
9
5 hyd.
2 elec.
12 elec.
8 hyd.
6 elec.
8 elec.
10
4-500
78.250
41.472
688.602
70.870
220.090
11
30.91
8.25
17.42
19.88
23.II
6.71
12
1,001.5
4,626.0
5,201.5
98,553-6
12,007.5
10,789.3
13
3-96I
50. 700
16.165
3H.666
68.625
45.OOO
14
$ 40.74
183.74
185.23
L 753-31
403.37
338.12
15
SS
64
38
45
96
20
DICKER AND KIRK: LIGHTING IN OFFICE BUILDINGS 665
Similarly the second portion contains data on elevators and
public lamps.
This table contains a separation of Table II-A showing the
same data on that part of the total service which is used for
elevators and public lamps.2
The percentage of this portion of the electric consumption to
the total building consumption is shown below :
Building Per cent.
No. 1 13-3
No. 2 64.1
No. 3 ?5-9
No. 4s 89.1
No. 5 65.8
No. 6 67.5
or an average of 39.3 per cent, for all of the buildings (excluding
No. 4).
TABLE II-C— Comparative Lighting Data.
Offices
Bldg.
Connected
load Kw.
Load-
factor
Number
offices
occupied
Av. Kw-h.
per office
per month
Av. max.
per office
per month
Av. net bill
per office
per month
Ratio of
max. to
connected
load
I
2
3
4
5
6
16
73-748
80.960
307.242
I5I-6S3
II2.900
53-90I
17
6.76
4.64
5.22
6.16
4.70
2.43
18
88
80
305
73
60
3i
19
40.6
32.3
37-8
92.1
64.8
95-6
20
0.632
0.684
0.667
1. 2l8
O.936
I.32
21
$2.62
2.17
2.24
4-97
4.09
5.82
22
75
64
66
58
49
76
Here are displayed the same conditions applied to the
office or rentable area of the building. This portion represents
17.0 per cent, of the total building consumption. The tenant's
load-factor is extremely low, showing a use of the demand of
from one half to one and one half hours per day. The minimum
load-factor occurs in the newest building. This is due to the
fact that the building occupies a small land area with good ex-
posure facing Lake Michigan, and it is higher than the surround-
2 Public lamps include all lighting contained in or around building which is not
chargeable to tenants' meters, t. e., corridors, exterior lighting, toilets, etc. Elevators
include all electricity used for power purposes.
8 This includes power for printing presses and is therefore not typical for this class of
ouilding.
666 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
ing buildings. The conditions make daytime burning of lamps
unnecessary in many of the offices.
TABLE II-D. — Comparative Lighting Data.
Store
space
Bldg.
Connected
load Kw.
I<oad-
factor
Av. Kw-h.
per month
Av. max.
Kw.
per month
Av. net
bill
per month
Ratio of
max. to
connected
load
per cent.
23
24
25
26
27
28
I
2I.86o
18.78
2,955-7
IO.4
$116.63
47
2
80.960
4.64
32-3
O.68
2.17
67
3
31.410
14.62
3,307-0
12.6
I37-40
40
4
37-538
I9-25
6,203.3
23.6
230.45
63
5
I.5.3II
20.97
2,343-2
9.6
96.41
63
6
68.899
4-32
2,223.2
10. 1
92.15
14
Inasmuch as the store and shop areas on the first and second
floors represent a load-factor of considerably higher value than
the office space, a further separation has been made. In this
table the load used by the store or shop is analyzed. This portion
represents 9.5 per cent, of the total building consumption. It
will be noted that the average load-factor of this portion of the
building is 13.76 per cent. (3.3 hours) as against 4.99 per cent.
(1.2 hours) for the office portion, and the ratio of maximum
demand to connected load is 49.3 per cent, for this portion as
against 73.3 per cent, for the office portion, which shows the store
to be the longer-hour user, while the office uses a higher propor-
tion of the connected load for a very short time. The former load
is by far the most desirable one from the central-station point of
view. The fact that the office uses the lamps for such a short
period is probably the reason that the office is the most dilatory
in considering lighting improvement; but, as already stated, the
time that the office requires light — short though it may be — is
the very time that light is most essential.
Table II-E sums up all the lighting data which have preceded.
It will be noted that during the thirty years there has been little
change in the watts per square foot provided, while the intensity
has increased with each period and the cost per square foot has
decreased. It must be borne in mind that the reason for the
fact that the provided load has not increased during this thirty-
Fig. i.— An installation in the oldest office building.
Fig. 2. — An installation in the newest building.
..,-'
FOOT-CANDLES -
-
»*--*"
,.--
-""
-"
YEARS
Curve i.
Curve 2.
DICKER AND KIRK: LIGHTING IN OFFICE BUILDINGS 667
year period is because the older buildings were not provided with
what is to-day called sufficient illumination, together with the
increased efficiency of illuminants. The standards of to-day are
greatly in excess of those of previous years. These relations are
shown graphically in curves 1 and 2.
TABLE II-E.— Comparative Lighting Data.
Bldg.
Watts per sq. ft.
Intensity
foot-candles
Cost of light per
sq. ft. per month
1
I
2
3
4
5
6
29
I.02
0.75
I.09
I.24
O.94
I.02
3°
1-5
2.0
3-o
3-5
4.0
4-5
31
$0,042
0.018
O.03I
0.029
O.025
O.OI6
Curve 1 shows the increased intensity of illumination with
practically the same provided load.
Curve 2 shows the reduction in cost of electric light due to
increased efficiency of illuminants and fixtures. Curve 3 shows
the reduction in cost due to increased efficiency of illuminant,
fixtures and reduction in rates for lighting.
Table III shows data on the office portion of the first four
buildings using carbon lamps as was the case when the lighting
systems were installed. In this table the rating of the lamp is
five watts per candle. The cost data are shown graphically on
curve 3.
TABLE III.— Carbon Lamp.
Offices.
Bldg.
Connected
load Kw.
Per cent,
ratio of
max. to
connected
load
Per cent,
load-factor
Average
Kw-h.
per office
per month
Average
net bill
per month
per office
Cost in cents
per sq. ft.
per month
I
2
3
4
368.740
404.800
1,536.210
758.415
75-48
67.18
66.282
58.607
6.764
4.64
5-223
6.162
203.325
161.650
189.400
460.915
|I3.I2
IO.86
II.24
24.89
3-975
1. 810
2.810
6.220
Progress during these thirty years may be very forcefully shown
5
668 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
by a comparison of the two photographs. The first one is of an
original installation in the oldest building and the second of the
newest installation in the newest building. These two pictures
indicate two extremes : one is merely a method of supporting the
light source, the other an efficient ornate lighting fixture.
DISCUSSION.
Mr. G. H. Stickney: There are a few classes of workers
who are subjected to more severe eye-strain than office employees.
Casual observation will show many examples of inadequate and
glaring illumination. It is to be hoped, therefore, that the ex-
cellent papers dealing with this subject will be influential in bet-
tering conditions.
Owing to the crowding of buildings in our large cities, artificial
lighting is used to supplement daylight fully as much as for night
work. When used in the daytime a higher intensity is demanded
than for night work. On the other hand glare effect is less ser-
ious. I have in mind an office illuminated by direct lighting
which in the evening appears glary and somewhat overlighted,
but in the dusk, which represents the period of maximum use,
the lighting is unusually good. I mention this to bring out the
point that an installation often has two distinct requirements to
meet which may necessitate a compromise in the design. In gen-
eral it is apparent that the practise in office lighting is tending
strongly toward the use of the semi-indirect and indirect types
of equipment and with this is coming a considerable improvement
in the standard of office lighting.
Mr. G. S. Barrows: This paper states: "It so happens that
the oldest building chosen is one in which the owners had fore-
sight enough at the time of its construction to wire for elec-
tricity." That building has been built about 30 years and I won-
der if the wiring put in at that time will meet with the approval
of the underwriters. I should like to ask the authors if they
found it necessary to change the wiring in this building. I think
that is a point that possibly is being lost sight of in an attempt to
simply provide for proper illumination. It seems to me that it is
most desirable for us to impress on architects and builders the
LIGHTING IN OFFICE BUILDINGS 669
necessity of providing for proper wiring and also gas piping in
all buildings that are being erected. There is no telling what the
developments may be in the future and provision should be made
for the use of either form of energy. The cost of providing for
either electric wiring of any kind, that is, providing for wiring
that may be done at some future time, in accordance with some
future ruling of the underwriters, or the installation of gas
piping is but a very small fraction of a per cent, of the total cost
of the building; whereas after the building is erected, the
proper wiring or piping may amount to a very large per cent, of
the total cost of the building. Beyond the simple use of energy
for light there is no telling what the developments may be for
the use of energy for some other purpose, for heating or we don't
know what, and so I think that as illuminating engineers, or as
engineers, I should say, we ought to go a little further than sim-
ply taking care of the illumination at the present time. We ought
to impress on the architects and builders to provide, as far
as they can, for all future demands. That question has been, and
is being, pretty carefully studied by a good many people at the
present time and I think we should provide for supplying in the
future energy for almost any purpose.
Mr. James J. Kirk : I might say a few words in regard to
the wiring conditions of the building that was built 30 years ago.
At the time this building was completed it was inspected and was
passed by the City Inspection Department. Since that time it
has been reinspected for defective wiring. Wiring for new in-
stallations have also been made in accordance with the latest rules
of the Department of Gas and Electricity.
6/0 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
PILOT FLAME IGNITION OF INCANDESCENT
GAS LAMPS *
BY C. W. JORDAN.
Synopsis: Despite the fact that many ingenious mechanisms have
been devised for securing automatic distance ignition of gas lamps, the
simple by-pass pilot flame remains as the most positive, serviceable and
economical. A description of various types of pilot tips and by-passes is
given, together with illustrations of the most successful types. The
troubles which are often encountered in service are enumerated, as well
as means which have been devised for their elimination. The application
of a new type of pilot in giving ample general illumination to distinguish
objects in rooms at night is described in detail.
INTRODUCTION.
The subject of pilot flame ignition of incandescent gas lamps
may appear to many to be rather a minor or unimportant detail
of the broad general subject of gas lighting, and yet on analysis
it will be found to be extremely vital for the successful operation
of lamps in practise.
Convenience in gas lighting has become a necessity and many
devices have been perfected for securing automatic ignition, in
some cases controlled from distant points.1- 2-
Despite the ingenuity shown in the design and mechanical con-
struction of these devices, for one reason or another they have
not recommended themselves as competent to meet the practical
requirements of service.
Those which are apparently satisfactory automatically actuate
a mechanism, turning on the main gas supply which in turn is
ignited by means of a pilot flame. Therefore the convenience of
such mechanical devices is dependent not only upon their own
merits, but also upon that of the pilot.
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, 191 5-
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
1 Gilpin, F. H., Automatic and Distant lighters ; Proceedings A. G. I., vol VIII, 1913,
Part II.
2 Jordan, C.W., Recent Advances in Indoor Gas lighting; Trans. I. E- S., vol. IX, 1914.
JORDAN: INCANDESCENT GAS LAMPS 671
Other devices, which do not use pilots, while ingenious, well
constructed and positive in action, owing to their high initial cost
do not find wide application.
Pyrophoric igniters, self-lighting mantles, etc., are not exten-
sively used because of the ease with which the mechanical parts
get out of order or on account of the short life of the active
material.
The simple pilot by-pass and gas cock actuated by pulling a
chain meet the demand for convenience, economy and service in
the most satisfactory manner.
This paper, therefore, will be devoted to telling the history of
the use and improvement of this simple means of ignition, which
depends upon the same energy or fuel that supplies the lamp
itself, and which is operated by the same mechanical movement
that controls the lamp. Every consideration points to this as the
ideal as well as common sense method of ignition, if it can be
perfected.
PILOT BY-PASSES.
The term pilot by-pass may be defined as a device by means of
which a supply of gas is regulated and led from a point just
ahead of the gas cock of a lamp to a pilot tip or point of dis-
charge conveniently placed near the mantle.
The gas cock and pilot take-off are in some cases of separate
construction from the lamp and easily detachable, while in others
they constitute a true part of the lamp construction.
The length of the pilot flame is regulated by turning a small
screw which moves in or out of a constriction in the passageway
leading to the pilot tip.
In some instances lamps are equipped with so-called "flash
pilots." A flash pilot may be defined as one in which the pilot
momentarily elongates during ignition and shoots across the top
of or into one or more mantles of the lamp. The means for
successfully accomplishing this are several.
In one lamp a secondary cock is connected to the primary gas
cock so that upon pulling the chain to light the lamp it is turned
1800 and the gas passes through to the pilot tip at unrestricted
pressure, by-passing the ordinary regulating screw.
Another device consists of an additional passageway bored in
6/2 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
the gas cock, which on being turned on supplies gas at unrestricted
pressure through a small tube by-passing the regulating screw.
When the cock is turned on full the passageway in the gas cock
is no longer opposite the passageway leading around the regu-
lating screw and the gas to the pilot is supplied only through
the usual regulating screw.
Flash pilots are effective, especially in arc lamps, in that they
secure more positive and softer ignition of all the mantles.
PILOT TIPS.
Little trouble has been experienced in constructing efficient
means for regulating and conveying the pilot gas supply to the
point of discharge, but the construction of a satisfactory pilot tip,
especially for inverted lamps, has been very difficult.
The main troubles encountered are (1) carbon formation, (2)
clogging of the tip, due to disintegration of the gas, etc., and
(3) the ease of extinguishing the flame by draughts.
With upright lamps a plain metal tube of small diameter, placed
properly in a vertical position, burns satisfactorily, but the flame
is easily extinguished if the lamp is subjected to excessive
draughts.
A center pilot was then designed which consists, briefly, of
placing the pilot flame directly above and in the center of the
burner cap gauze, thus utilizing the mantle as a means of effec-
tively protecting the flame from draught. The construction of
a center pilot by-pass is shown in Fig. 1.
With inverted lamps it was necessary to use pilot tips made of
lava or other refractory material in order to overcome the com-
mon troubles before mentioned.
Lava pilot tips have undergone decided changes, both in the
principle upon which they operate and in design. The first type
consisted of a simple passage, drilled through the tube and having
a side outlet for discharging a luminous flame horizontally. A
pilot tip was then developed which gives a blue Bunsen flame
while burning. The gas discharges horizontally through a small
orifice into a mixing tube provided with two air inlets. When
operating at normal consumptions, between 0.1 and 0.15 cu. ft.
per hour, a perfect Bunsen flame is obtained which is extinguished
by draught with far greater difficulty than the luminous flame
JORDAN: INCANDESCENT GAS LAMPS
673
pilot and has the additional advantage of eliminating troublesome
carbon formation or smoky flame. Changing the position of the
primary air inlets from a vertical to a horizontal position was
found to render the pilot appreciably more resistant to draughts.
Six types of lava tips are shown in Fig. 2.
In the early development of the Bunsen flame pilot a series of
unlooked-for defects were found, a description of which may be
of interest. In order to obtain a true Bunsen flame it is necessary
to make the orifice of very small diameter, 0.016 in. (0.40 mm.).
After several hundred hours burning of the lamp the orifices
invariably become clogged. The tips were made of natural lava,
A- LUMINOUS F1AMT. LAVA TIP
3- EUNSEH FLAME LAVA TIP- tEKncAl NA H0l£S
C" EUHStW CLAMB LAVA TrP- HORIZONTAL AIR MOLES
P-FAHSHATCD LUMIMCL5 FLAME LAVA TIP
C SL'fCtK FLAME LAVATtP.
T- SEMI- BUNSEN FLAME METAL TIP
Fig. 1.— Center pilot burner.
Fig. 2.
baked, and on the interior a hard glossy coating of carbon,
resembling flaked graphite, was found. This extended through
the entire passageway to the orifice which, on account of its small
diameter, became stopped first. An investigation was made and
it was found that the decomposition of the hydrocarbons in the
gas to carbon was influenced not only by the high local tempera-
ture (6200 C. at the orifice), but also by the physical properties
of the substance used in construction. By using a tip made of
finely crushed natural lava, repressed and baked, the trouble was
practically eliminated. A small amount of carbon formed in the
passageways, which was grayish instead of black, and after the
674 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
lamps were burned several thousand hours was found not to give
trouble.
An interesting series of experiments was made, the results of
which clearly illustrate the influence of the physical and chemical
properties of the pilot tip material upon the decomposition of the
gas. Various substances were placed in a transparent quartz
tube, through which illuminating gas was passed, and heated
Fig- 3-
slowly and uniformly by means of an electric furnace. Certain
substances, like metallic oxides (particularly mantle ash) became
covered with carbon at a temperature as low as 2600 C, while
others, like glass, quartz, etc., only darkened at a temperature of
above 650 ° C.
A still more recent change has occurred both in the design of
pilot tips and in the position in which they burn. The pilot tip
of the lamp shown in Fig. 3 is mounted vertically and in this
JORDAN: INCANDESCENT GAS EAMPS 675
position the flame is very well protected from draughts and at
the same time is positive in its ignition of the mantle.
The advantages of this type of tip are (1) that there is no
orifice which may become clogged with carbon from the decom-
position of gas, (2) in case the pilot flame becomes overadjusted
there is no danger of cracking the enclosing glass cylinder,
and (3) that when subjected to excessive draught the pilot flame
retreats within the pilot tip and is effectively protected.
SERVICE TROUBLES.
Pilot devices are subject to numerous troubles in service. In
certain localities the methods of manufacturing and purifying
gas are liable to change suddenly from normal and often tar
particles are carried in suspension by the gas for considerable
distances from the works. In this event the tar rapidly accumu-
lates on the pilot adjusting needles of the lamps and completely
closes the minute annular opening through which the gas dis-
charges. In order to overcome this trouble a purifying device,
shown in Fig. 4, was designed. Essentially it consists of passing
the gas through a small cylindrical brass tube which has been
packed with asbestos wool, glass wool, mineral wool or other
suitable material. The gas to the pilot flame is completely
detarred by this method for a long period. When the filtering
material becomes clogged or saturated, the brass tube is removed,
cleaned and repacked. This simple device has proven to be very
effective and in a few instances absolutely essential for the proper
working of pilots.
Pilot outage due to draughts is a condition which lamp manu-
facturers have been attempting to minimize and eliminate. The
seriousness of this trouble is primarily dependent upon the con-
ditions under which the lamp burns and whether it is an indoor
or outdoor lamp.
The luminous flame pilot is far from desirable in this respect,
unless it is properly surrounded by a protecting casing in which
case it is very liable to carbonize. With upright lamps the pilots
can be readily enclosed by the mantle (see Fig. 1) and are thus
very efficiently protected.
In the case of inverted lamps the problem was more difficult.
Investigation led to the adoption of the Bunsen flame pilot tip
676 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
and finally in a later modification to a type which is very difficult
to extinguish (see Fig. 3).
With outdoor lamps the use of semi-Bunsen pilots, surrounded
by a protecting casing (see Fig. 5), has proven very satisfactory.
Radical changes in the construction of pilot tips, being experi-
mented with at present, give promise of producing a practically
inextinguishable pilot in the near future.
PILOT CONSUMPTION.
A consideration of the consumption of gas by pilots is of
importance in that consumers are often badly misinformed or
entirely ignorant of its magnitude. The consumption is not only
influenced by the length of flame which is judged adequate by
the adjuster, but also upon the particular type of pilot by-pass
used.
The so-called "sub-flame" pilot by-pass is in reality a simple
device for turning low a gas lamp. As the flame must burn over
the entire surface of the burner gauze without danger of flash-
back, the consumption is naturally greater than that of an ordi-
nary pilot.
The use of the "sub-flame" pilot by-pass is rather limited and
the pilot consumption should not be taken as representative of
the more efficient types.
The following table shows the normal consumptions of various
types of indoor and outdoor lamps and the ratios of the total
gas consumption to that of the pilot consumption.
Approx.
Normal length
pilot cons. of
per hour flame
I,amp (Cu. ft.) (Inches)
i burner inverted indoor,
Bunsen pilot 0.120 %
1 burner upright indoor,
luminous pilot 0.095 %
3 burner inverted indoor
arc, semi-Bunsen pilot 0.147 V%
5 burner inverted outdoor
arc, semi-Bunsen pilot 0.213 %
1 burner inverted outdoor,
luminous pilot 0.152 ys i33!-5 3-45 5.°37 20.9
These calculations are made on the assumption that the lamps
Pilot
ons. per
year
(Cu. ft.)
Normal
lamp
cons.
per hour
(Cu. ft.)
I,amp
cons,
per year
4 hrs.
daily
(Cu. ft.)
Pilot
cons.
per cent.
of total
cons.
1051.2
3-50
5»110
I7.I
832.2
4.65
6,789
IO.9
1287.7
IO.OO
14,600
8.1
1865.9
I7-50
25.55o
6.S
JORDAN : INCANDESCENT GAS LAMPS
677
operate on mixed gas at 2.5 in. (63.5 mm.) pressure,
value 650 B. t. u. per cu. ft. ; specific gravity 0.660.
Total heat
NOVEL USE OF BLUE FLAME PILOTS.
As mentioned before, the essential reasons for changing from
the luminous flame to the non-luminous Bunsen flame pilot were
because of the greater difficulty of extinguishing the flame of
the latter by draughts and the elimination of troublesome carbon
formation or smoky flames.
In addition to these features the non-luminous flame lends itself
to a novel and efficient use. It has long been contended that the
luminous flame pilot instead of being considered a necessary
expensive accessory of a gas lamp is in reality an efficient adjunct,
in that it serves the purpose of guidance to the consumer desiring
in turning on a lamp in a dark room.3 By placing the Bunsen
flame pilot so as to impinge to the extent desired upon the mantle
an increase in the intensity of light of over five times that of the
luminous flame pilot is obtained.
J*\
Fig. 4.— Tar scrubber.
Fig. 5.— Semi-Bunsen protected pilot.
The following table shows the maximum horizontal candle-
power obtained from the two types of pilot flames:
Max. horizontal Corr. cons, candlepower
Type flame candlepower cu. ft. hour per cu. ft.
Bunsen flame 0.1612 0.126 1.28
Luminous flame 0.0319 0.130 0.245
Open flame candlepower of gas burned in 8 ft. tip 22.0 at a 5 ft.
rate.
Litle, T. J., Convenience of Gas Lighting, Trans. I. E. S., vol. IV, 1909.
678 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
The increase in intensity not only serves as a better guidance
in turning on the lamps at night, but to the dark adapted eyes it
affords sufficient illumination to comfortably distinguish many
objects in an ordinary living room. This is obtained at a cost
no greater than that of maintaining the luminous pilot flame. In
addition it is more difficult to extinguish the flame of a pilot
impinging on the mantle.
In cases where pilot illumination would be objectionable, it is
merely necessary to turn the pilot flame aside from the mantles
and practically no light is obtained.
Physical Laboratory,
The United Gas Improvement Co.,
Philadelphia, Pa.
Sept. 3, 1915.
DISCUSSION.
Mr. F. A. Vaughn: I am particularly interested in the
pilot light and the automatic lighter and extinguisher for street
lighting gas lamps and if there is any one in the room who could
give me any information on this particular application of the
pilot, I would be very glad.
Mr. T. J. LitlE: There is an erroneous impression among a
great many people that the average pilot flame burner in the
house consumes a great deal of gas. The pilot, as Mr. Jordan
has very clearly shown in his paper, not only serves as a form
of ignition for the gas burner itself, but also serves to give
enough illumination in the room to be used as a night lamp, etc.
Now that in itself is extremely valuable. The pilot on a gas
lamp in a room can be said to perform the same function as the
electric lamp that can be turned low by the pull of the chain.
The pilot will enable one to see about the room and it must be
considered as part of the illumination. Considering the con-
venience and very slight expense of such an arrangement for
the various rooms in a house, I think it is possibly the cheapest
form of night illumination.
Mr. Vaughn asked a question regarding street lamps. It is
the practise in using pilots on street lamps, or for lamps used
commercially in front of buildings, to protect the flame by some
draft-proof arrangement. In Europe and America the usual
INCANDESCENT GAS LAMPS 679
practise is to use a perforated cup. This scheme is working out
very well. Remote control of street lamps and the clock and
pressure wave lighting systems have been tried.
Mr. C. W. Jordan : In reply to Mr. Vaughn's inquiry regard-
ing automatic igniters, I wish to refer him to an article published
in the American Gas Institute Proceedings, Vol. VIII, 1913,
Part II, by Mr. F. H. Gilpin, entitled "Automatic and Distant
Lighters." This article thoroughly covers the application of
many types of automatic igniters to American practise under the
existing climatic conditions.
680 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
THE LIGHTING OF A PASSENGER STEAMER.*
BY H. T. SPAULDING.
Synopsis: This paper introduces the subject by a brief historical
sketch of past and present practise in marine lighting. The lighting
requirements of a passenger boat are discussed and compared with
similar installations ashore. To illustrate how these requirements can
be satisfied the author describes the lighting system designed by him, in
co-operation with the architects, for the S. S. Noronic, a lake passenger
boat, and gives the results of illumination tests in some of the more
important portions of the vessel. In conclusion it is recommended that
a departure be made from the ordinary boat lighting systems so common
at present, and it is urged that a closer relationship between marine archi-
tects and illuminating engineers be established.
Boat lighting is similar with regard to the question of utiliza-
tion efficiency and choice of system of illumination to installations
on land having similar requirements, and it is therefore not the
intention in this paper to cover these subjects. There are, how-
ever, certain factors governing marine lighting which are dif-
ferent from those usually encountered, and it is these factors, to-
gether with the requirements, and the manner in which they can
be satisfied, that are to be discussed and illustrated by means of
a description of the lighting of the S. S. Noronic, which was de-
signed by the writer in co-operation with the architects of the
interior finish and decoration.
There is a tendency among marine engineers to regard the cost
of generating power as a small item, and this has resulted in
the continued use of carbon lamps to a considerable extent for
boat lighting. Insufficient attention has also been given to the in-
stallation of the lamps and their equipment to conform with the
principles of good lighting, and reduction of glare. It is not un-
common to find a boat with elaborate equipment in all other re-
spects fitted with bare lamps studded in the ceiling, or perhaps,
equipped with so-called decorative glassware mounted upon
fixtures at such a height that they are directly in the line of
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, J9i 5-
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
spaueding: lighting of a passenger steamer 68i
vision. This is well illustrated in a paper1 read before the New
York section about three and a half years ago which was de-
scriptive of the lighting systems on a number of boats of various
classes in service at that time. Figs, i and 2, which are photo-
graphs of the social hall and dining room respectively on one of
our lake boats, show installations typical of the methods com-
monly employed. In Fig. 1 the lighting units shown are all-
frosted carbon lamps. The lighting of the dining room is more
satisfactory as tungsten filament lamps are used and glare is
somewhat reduced by means of diffusing glassware. The lighting
is, however, hardly in keeping with the remainder of the ap-
pointments of the boat. No radical changes in the methods illus-
trated have been made in the last few years, except in the case of
a few of the more recent, larger boats.
A passenger boat has requirements similar to a hotel, with its
divisions corresponding on a smaller scale to the rooms used for
similar purposes on land. The entrance hall, like a hotel lobby,
should be brilliantly lighted. Social halls, as a rule, require less
illumination; but as these rooms are often used for reading, it
is necessary that the light be well diffused, and glare eliminated.
Enclosing glassware, semi-indirect, or indirect fixtures will ful-
fill the requirements but usually the low ceiling height interferes
with the use of the last two systems. For parlors, observation
rooms, drawing rooms, and smoking rooms similar requirements,
and also the same limitations, exist. Dining rooms should have a
higher intensity, and here it is often possible to make use of semi-
indirect lighting regardless of the low ceiling. As the tables are
usually fixed, lighting units located directly above them will not
interfere with the necessary head room.
The more pretentious suits are very similar to hotel guest
rooms in every respect, and their lighting requirements are iden-
tical, but the ordinary staterooms require a different treatment.
They are usually of such a size that a single low wattage lamp
is ample for all needs, and the small space between decks, to-
gether with the berth arrangement, practically limits the location
to the side walls. This is one of the few places on a boat where
the use of bare, all-frosted lamps cannot be criticized, although
1 Porter I,. C, The Lighting of Passenger Vessels; Trans. I. E. S. Vol. VII, p. 116,
1912.
682 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
equally satisfactory illumination and improved appearance will
obtain if clear lamps equipped with diffusing glassware are
used. Berth lights similar to those used in train lighting are a
convenience greatly appreciated, and should be installed when-
ever the expense is not considered prohibitive. Writing rooms,
barber shops, lavatories, passages etc., can generally be treated
in the usual manner. An appendix is attached giving the inten-
sities of illumination to be recommended and the equipment de-
sirable for lighting the various portions of a passenger boat.
Mention has been made above to the limitations imposed due to
the low ceilings almost universally found on boats. The space
between decks is not often over 8 ft. (2.44 m.), usually less, so
that by the time the thickness of the deck, the depth of the deck
beams and the ceiling finish are subtracted, there is little space
available for the lighting unit. Steel deck beams are common,
and increase the difficulties of electrical construction. Usually the
floor of the deck above forms the ceiling of the one below, and
hence there is no space in which the wiring can be concealed or
the lighting units recessed. Shallow bowls, very close ceiling
fixtures, or a suspended ceiling with recessed lighting units, are
some of the methods in which the difficulty can be overcome.
Wall brackets, or lamps set into the partitions behind diffusing
plaques can also be employed in certain cases. Generally, how-
ever, the necessity for utilizing all possible space has resulted in
the partitions being constructed of but a single thickness of wood,
so that there is little chance of recessing the units ; in fact there
is little space in which to run conduit for wall brackets.
The Northern Navigation Company's S. S. Noronic was de-
signed to be one of the best and most completely equipped boats
upon the lakes, and the finish, furnishings and lighting equipment
were given more than usual consideration. Five decks are de-
voted wholly or in part to the use of the public. At the entrance
on the main deck, a small hall, panelled in oak, leads to the stair-
way to the spar deck. Here are the office and lobby. On this
deck are also located 150 staterooms, each equipped with hot and
cold running water. The promenade deck above contains the
smoking room, ladies' drawing room or lounge, 10 parlor rooms,
social hall, and additional state rooms. The finish throughout is
Fig. i.— Social hall of lake passenger boat.
Fig. 2.— Dining room of lake passenger boat.
spaulding: lighting of a passenger steamer 683
in panelled mahogany. The public portion of the fourth or ob-
servation deck consists of only two rooms, the observation room
and the dining room, with an orchestra platform between. The
dining room is finished in mahogany and light green, while the
observation room, enclosed on three sides by large windows, has
rugs, upholstery, hangings, and woodwork in a greenish gray
tone. The boat deck contains, in addition to the pilot house and
officers' quarters, a social hall panelled in light oak which is util-
ized as a writing room. Fig. 3 which is a plan view of the various
decks, shows the arrangement of these rooms, and the location of
all lighting outlets in the public areas of the boat.
In designing the lighting system, the unusual good fortune
was experienced of being called upon before the plans of the
interior were complete, and within limits, other considerations
were secondary to the satisfaction of the principles of good
lighting and the architectural requirements. The following para-
graphs describe the lighting units installed and some of the
features influencing their choice.
The lighting of the dining room is somewhat of a departure
from the usual methods, in that semi-indirect lighting was em-
ployed with the outlets so arranged that a bowl was suspended
directly over each table. A ceiling at the level of the under side
of the deck beams was provided with a small circular panel above
the lighting unit, recessed, and finished with a smooth surface, so
that the brightly lighted area directly above the lamp was cir-
cumscribed. Even with the low ceiling height, about 7 ft.
(2.13 m.), and the short fixture length, this arrangement re-
sulted in the ceiling appearing fairly uniformly lighted, and pro-
vided a contrast to the relief decorations upon the remainder of
the ceiling. To insure that the entire effect would be pleasing, a
full sized model of a portion of the ceiling was constructed and
a large number of bowl and lamp combinations were investigated
before the one finally approved was adopted. A heavy density
bowl2 16 in. (40.64 cm.), in diameter, etched with a special de-
sign harmonizing with the decorations as shown in Fig. 4a, was
used with a 100-watt round bulb lamp. Fig. 5 is a view of the
room with the lamps on. Illumination readings in a horizontal
plane at the table level were taken in the representative area
2 No. 1265 Calla 72 bowl.
684 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
C-BOAT DECK
e-5MOKING-f?00M S'SOCIAL HALLS-WALLS
f-5QCIAL HALLS -CEILING BEAMS
h-ENTRANCE HALL
Fig. 4.— Fixture designs for S. S. Noronic.
spaulding: lighting of a passenger steamer 685
shown by the shading in Fig. 3. At the time of the test the boat
was not in commission, and the voltage was about 3 volts below
normal. The lamps had been burned over half their rated life,
and lamps and glassware were, not cleaned previous to the test,
so that the intensity of 3.7 foot-candles obtained after correcting
for voltage is indicative of average conditions.
The low clearance in the observation room prevented the use
of any type of fixture which would project far down from the
ceiling, and the area of the room was such that lighting from the
side would not have produced satisfactory effects. It was possi-
ble, however, to employ a suspended ceiling, with a few inches
between the ceiling and the deck above in which the lamps could
be recessed, and this course was decided upon. An eliptical dish3
was used as a relief from the uniformity of the square ceiling
panels. In the opinion of the architect it was also desirable be-
cause of the note of individuality conveyed. A single 100-watt
round bulb lamp, backed by a white enamelled reflector was
made use of for these fixtures as shown in Fig. 4b. It would have
been possible to have a more shallow dish with two lamps burn-
ing horizontally except for the fact that the architect, for esthetic
reasons, desired that the dish should not be lighted with absolute
uniformity, but should show a brighter area near the center. A
test in the area shown, with conditions as outlined above, gave
1.8 foot-candles in a horizontal plane 2.5 ft. (0.762 m.) above
the floor. Fig. 6 is a daylight view of this room with the lights
on.
For lighting the writing room or social hall on the boat deck,
and for the portion of the promenade deck below the light well
extending down through two decks, a single row of 250 watt
lamps, with totally-enclosing diffusing globes4 of the design
shown in Fig. 4c, were located on the ceiling of the boat deck.
The smoking room and lobby were handled in about the same
manner. The "squat" ceiling bowls shown in detail in Fig. 4d
and 4e were used. Shallow bowls were necessary in these loca-
tions to allow of sufficient headroom, and a heavy density glass
was chosen to conceal the lamp filament. Twenty-five-watt
3 Alba glass No. 3772.
* Druid glass No. 01218 12 in.
686 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
lamps were used in the 6-inch (15.25 cm.) bowls5 in the smok-
ing room; and the 10-inch (25.4 cm.) bowls0 in the lobby were
equipped with 100-watt lamps. Here, as in a number of other
locations, it was necessary to use the round bulb lamp because
of its shorter over-all length.
The ceilings of the lounge, and the social halls on the spar and
promenade decks were beamed, with insufficient room below to
permit the use of even a shallow dish, and with so small a space
between the ceiling in the panelled portions and the floor above,
as to prevent the location of units in these areas. It was found
that the narrow hallways and the portions of the larger rooms
adjacent to the walls could be cared for by means of side light-
ing. For this purpose the oblong plaques7 shown in Fig. 4f were
developed. The illumination of the central portions of the larger
areas was brought up by recessing larger plaques8 of a similar
shape in the sides of the ceiling beams. A single 60-watt lamp
was used in the wall outlets, and those on the beams contained
either two 25-watt or two 60-watt lamps, depending upon the
location. Details of the larger units are shown in Fig. 2g. Illum-
ination measurements taken at representative points showed an
illumination upon a horizontal plane 2.5 ft. (0.762 m.) above the
floor averaging about 0.7 foot-candles. The vertical illumination
was higher, and as the function of the lighting in most of these
portions is only to enable the passengers to see their way around,
the results were satisfactory. In those rooms which were likely
to be used for reading, a higher wattage was installed, so that the
illumination was ample. Fig. 7 shows the lighting of the social
hall on the promenade deck, and also the units installed on the
ceiling of the boat deck above the well.
The entrance hall on the main deck was also lighted by means
of wall plaques,9 but of a somewhat different design. The means
which it was necessary to employ to obtain sufficient wattage in
the allowable space is shown in Fig. 4I1.
The lighting of the staterooms was accomplished, as is the
usual custom, by means of all frosted lamps on wall brackets at
6 Sudan glass No. 431 6 in.
6 Calla glass No. 328 10 in.
7 Alba glass No. 3370.
8 Alba glass No. 3771.
9 Sudan glass 4% in. X 2% in.
Fig. 5. — Dining room of S. S. Xoronic.
Fig. 6. — Observation room of S. S. Xoronic.
Fig. 7. — Social hall of S. S. Noronic.
Fig. 8.— Parlor room of S. S. Noronic.
spaulding: lighting of a passenger steamer
687
the side of the mirror. Each berth was also equipped with a
small lamp. The parlor rooms contained a number of wall
brackets fitted with dense opal shades as shown in Fig. 8.
While the illumination in no part of the boat might be con-
sidered as brilliant, yet it was found to be entirely satisfactory.
This is due in part to the isolation from other contrasting brilliant
illumination, but primarily to the fact that no bright light sources
are within the field of vision.
In conclusion, I wish to extend my thanks to the Northern
Navigation Co., the architects, the Holophane Works, and to Mr.
Ward Harrison, for co-operating in securing and preparing the
material for this paper.
APPENDIX
Recommendations for Passenger Boat Lighting.
Intensity
Location foot-candles Equipment and location
Baggage room 1. 0-1.5 Direct lighting — Glass reflectors at ceiling.
Ball room 2.0-3.0 Enclosing glassware at ceiling, or wall
fixtures.
Barber shop 4.0-5.0 Semi-indirect units over or near chairs.
Bath-room 1.5-2.0 Diffusing glassware, or all frosted lamps on
wall brackets at side of mirrors.
Cafe 1.5-2.5 Enclosing glassware, or direct reflectors of
warm tone on ceiling or wall fixtures.
Dining-room 3.0-4.0 Enclosing glasswase, or semi-indirect units.
Drawing-room 1.5-2.5 Enclosing glassware or wall fixtures.
Freight deck 0.5-1.0 Steel distributing reflectors.
Grand saloon 1.5-2.5 Enclosing glassware, semi-indirect, or wall
fixtures
Halls 1. 0-1.5 Wall fixtures.
Kitchen 2.0-3.0 Direct lighting — Glass reflectors at ceiling.
Lobby 1.5-2.5 Enclosing glassware, or wall fixtures.
Lounge r-5-2-5 Enclosing glassware, or wall fixtures.
Observation room .. 1.5-2.5 Enclosing glassware, or wall fixtures.
Office 3.0-4.0 Direct lighting glass reflectors at ceiling, or
on brackets over desks.
Parlor 1.5-2.5 Enclosing glassware, or wall fixtures.
Parlor rooms 1. 0-1.5 Wall brackets with diffusing glassware.
Passages 0.5-1.0 Wall fixtures.
Social hall 1.0-2.0 Wall fixtures, or enclosing glassware at ceiling.
State rooms-general — Diffusing glassware, or all frosted lamp on
bracket at side of mirror.
State rooms-berths. — Low candlepower all frosted lamp in each berth.
Toilets 1. 0-1.5 Direct lighting glass reflectors at ceiling, or
wall bracket with diffused glassware.
Writing rooms 2.5-4.0 Enclosing glassware at ceiling, or special
direct lighting on tables.
688 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
DISCUSSION.
Mr. L. C. Porter: It seems to me there is considerable dif-
ference in the illumination problems of ships and those on land,
because on most ships the finish is almost entirely white and this
makes considerable difference in figuring the amount of light
necessary. In regard to the tendency among marine engineers
to regard the cost as a small item — the cost of generating power
is not the only figure that enters into the calculation. The cost of
installation makes considerable difference. In ferryboat lighting
it is customary to use a large number of small lamps located on
each side of the passenger compartment. In a recent boat the
wattage was reduced to one half and the installation cost to
one third the figures considered common practise. This was
done by using a small number of large lighting units located down
the center of the cabin instead of a large number of small units
located in wall brackets.
The ceiling over the social hall (Fig. 7) is rather high. This
is the typical condition in river and lake steamers. For such
places having high ceiling room the open mouth reflectors can be
used to advantage and a little more efficiency gained than is
obtained through the totally enclosing globe.
The foot-candle illumination given for the observation room,
seems to be a little high. On the Washington Irving, the largest
river steamer in the world, a low illumination in the observation
room was desired because passengers usually like to see what is
outside, particularly along towards evening and at night. With
a high illumination inside the observation room one cannot see
the scenery outside as well as when there is a low illumination in
the observation room. I believe that half a foot-candle would
be much better than a value near two.
Mr. W. R. Moulton : The lighting problems in boat con-
struction are rather unusual, therefore very interesting. The
decoration of boat interiors is usually favorable to good lighting.
On the other hand special conditions confront one, such as the
low head room and the rafter ceiling construction.
I have recently had some interesting experience in lighting
two private yachts, where each room seemed to present a problem
of its own. In one the cabin was very low, and there was a
LIGHTING OF A PASSENGER STEAMER 689
birth seat along either side. Inverted brackets equipped with
heavy density opal reflectors were placed about 12 in. from the
ceiling. The upper side wall, the bulkhead and deck were
finished in light ivory which assisted in producing a very pleas-
ing lighting result. Light was reflected from the side wall and
also from the ceiling, and some penetrated the shades.
The pilot house ceiling was but 6 ft. 2 in. high. The owner
desired it lighted from a center ceiling outlet. It was necessary
to use a shallow bowl-shaped dome of medium density opal,
directly at the ceiling. This was about 8 in. in diameter and
about 3 in. deep. On account of the size of this unit it was im-
possible to use standard lamps; so two 15-watt candelabra base
tubular lamps were used. The use of special lamps for such
circumstances is surely justified.
On the same yacht electric running lights were installed. It
is a serious offense, subject to a heavy fine and also very danger-
ous, for a boat to operate without running lights burning. To
give proper warning as to the operation of the running lights,
tell-tale lamps were installed in the pilot house, connected in series
with the main lamps. If these tell-tale lamps were burning, they
indicated that the running lights also were burning. The tell-
tale light not burning, immediately warned the pilot of the outage
of his running light; he could then either replace the electric
bulb at once, or place a temporary oil lamp in its stead.
Mr. H. T. Spaulding (In reply) : There is only one point
which I wish to mention and that is in reference to the obser-
vation room. This area was also to be used at various times
as a ball room and consequently sufficient lighting for this use
had to be provided.
69O TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
SEMI-DIRECT OFFICE LIGHTING IN THE EDISON
BUILDING OF CHICAGO.*
BY WM. A. DURGIN AND J. B. JACKSON.
Synopsis: The equipment of a typical office test room and compara-
tive tests on five lighting systems to show relative eye fatigue, glare,
shadows, uniformity of intensity on desk plane, utilization efficiency and
effective flux color, are described. The test results, leading to the develop-
ment of a particular semi-direct unit for lighting the offices of the Com-
monwealth Edison Company, are discussed and the details of the adopted
fixture structure and glass bowl characteristics presented. Data are given
on the illuminating effectiveness, arrangement, appearance, and dust factor
of the completed installation, especial emphasis being placed upon the
importance of the use of higher intensities and filtered flux.
The great stride in the economical generation of light flux
achieved in the one-watt and higher efficiency incandescent lamps,
has enlarged the resources of the lighting engineer many fold.
In the age of the three-watt-per-candle lamp it was necessary to
consider all radiation which was capable of exciting the optic
nerve as valuable illuminating material if lighting was to be ac-
complished at reasonable cost, and the lowest intensity under
which seeing became moderately comfortable was perforce re-
garded as satisfactory. Flux generation at three to five times
this efficiency, however, permits economical use of much higher
intensities, and the filtering of the light to secure only those color
components which are best adapted to producing the desired ef-
fect.
Such higher intensities and controlled light quality may or may
not prove to be the ultimate solution of the good-lighting
problem. The possibilities at least are most attractive, but only
extended experience with installations involving considerable de-
partures from the current usage in intensity and flux color can
evaluate these characteristics.
The lighting of offices aggregating 82,000 sq. ft. (7,600 sq. m.)
for the use of one of the largest central station companies has
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, 191 5-
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
DURGIN AND JACKSON I SEMI-DIRECT OFFICE LIGHTING 69I
given opportunity for applying these ideas, and this paper pre-
sents some account of the preliminary tests of various possible
systems and of the development and final installation of a special
unit embodying the features of color modification and high in-
tensity while meeting the more generally recognized require-
ments of acceptable illumination.
For the preliminary tests a typical office in the new building
of the Commonwealth Edison Company was equipped with metal
moulding and outlets to permit a symmetrical two, four or six
unit installation. The room was approximately 24 ft. 6 in.
(7.5 m.) long, 19 ft. (5.8 m.) wide, and 10 ft. 6 in. (3.2 m.)
high. Three sides were clear wall space and although the fourth
or corridor side contained the door and a line of windows, all
glass was covered with heavy coatings of calcimine to match the
walls. With the exception then of the baseboard, chair rail,
picture moulding, lower panels of door, and frames of corridor
windows, all of which were finished in dark mahogany, the entire
wall surface of the room was calcimine.
The tints chosen were light cream for the ceiling (reflection
coefficient for vacuum tungsten lamp flux 0.8), dark cream for
the walls above chair rail (reflection coefficient 0.7), and light
brown below. The floor was bare maple. It was originally in-
tended to test several color schemes, but this first selection proved
so satisfactory to the committee charged with the final approval
of the installation that it was adopted and no other tints con-
sidered. An outline of the room showing position of the outlets,
as well as the desk employed in eye fatigue tests, is given in
Fig. 1.
Five distinct methods of office illumination were investigated:
direct lighting with prismatic reflectors in velvet finish; direct
lighting, with opal reflectors giving very light amber tone; semi-
direct lighting with art glass reflectors of amber tone; semi-direct
lighting with dense opal reflectors of slightly greenish tone; and
indirect lighting, with silvered glass reflectors. Each of these
systems was tested for eye fatigue, glare, shadows, color of the
light, uniformity of intensity on 30-inch desk plane, and utiliza-
tion efficiency for this plane. The detail of test equipment and
procedure will be found in Appendix I, the principal results being
summarized in Table I, and the following paragraphs :
692 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
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DURGIN AND JACKSON I SEMI-DIRECT OFFICE LIGHTING 693
TESTS.
Eye Fatigue. — The results of the Ferree tests made a part of
this investigation by Mr. J. R. Cravath have been presented pre-
viously to the society.1 The judgment of the subject in these
tests and of the present authors, a judgment substantiated as to
the order of excellence, if not entirely as to the degree of super-
iority, by the Ferree tests was as follows :
Both direct lighting systems showed marked inferiority to the
semi-direct and indirect systems when rated by eye fatigue. The
Fig. 1.— Plan of test room. Underlined figures indicate outlets used with
corresponding number of units in symmetrical arrangement.
preference of the testers was for the art glass semi-direct system
due probably to the amber tone of the light and the attractive ap-
pearance of the units, but both semi-direct installations were very
satisfactory.
Glare. — All observers were impressed with strain resulting
from the excessively bright walls under the direct system. As
1 Cravath, J. R., Some Experiments with the Ferree Test for Eye Fatigue ; Trans.
I. E. S., vol. IX, p. 1033 ; 1914.
694 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
computed from column 8, Table I, which gives the measured
value of the brightest area on the walls below the picture mould-
ing, the 100-watt direct units produced a wall brightness of the
order of one half that of a mat white paper on the desk plane,
deduced from the mean intensity shown in column 4, Table I.
The semi-direct system when reduced to the same horizontal il-
lumination gave only one third as high wall brightness, and with
the walls thus about one sixth as bright as the paper upon which
the observer was working no strain was noticed. The high wall
brightness shown under the indirect system is somewhat mis-
leading as it applied only to a narrow strip near the picture mould-
ing which would rarely come within the field of view. The test-
ers' judgment indicated that both semi-direct and indirect sys-
tems were satisfactory as regards wall glare, and that all three
were reasonably good in reducing desk glare, although the art
glass, semi-direct reflectors were of such light density as to be
inferior to the heavy density semi-direct and the indirect systems.
In the desk work with the direct system the surface reflection
glare from the desk top and glazed paper was very trying.
Ceiling brightness perhaps is rather outside the glare question
since in medium-sized offices ordinary lines of sight bring no
part of the ceiling into the field of view. It is interesting to note,
however, that, as shown in column 9, Table I, a small part of
the ceiling immediately above the direct units was quite as bright
as any part with the semi-direct units and two thirds as bright as
the ceiling illuminated with the indirect silvered reflectors when
the figures are reduced to the same horizontal illumination. This
unusual result was produced by the high mounting of the direct
units, which brought the glowing reflectors within a few inches
of the ceiling.
Shadows. — The bookkeeper working under the various sys-
tems was much annoyed by the multiple shadow from the two
six-unit direct lighting installations. While some shadow re-
sulted with the light density semi-direct system it produced no
comment and appeared acceptable to all observers for office work,
as did the almost total lack of shadow from the other two sys-
tems. Shadowgrams, made as outlined in Appendix I, served to
record the conditions of light direction for the inspection of the
DURGIN AND JACKSON '. SEMI-DIRECT OFFICE LIGHTING 695
lighting committee and to display the difference between the
clear-cut and comparatively dense shadows from the direct sys-
tem, and the hazy outline and lesser density of those from the
art-glass semi-direct installation. The practical equality of a
moderately dense bowl semi-direct system and the indirect sys-
tem in lack of shadow production was especially well shown and
it was agreed that each of these installations diffused the light too
much for the best esthetic effect.
Color of Light. — The warmer tone of light from the art-glass
semi-direct units was very agreeable, while the similar color from
the opal-glass direct system was responsible probably for a con-
siderable portion of its apparent visual superiority over the pris-
matic equipment. Both semi-direct and indirect systems took
their color tone to a marked extent from the ceiling and the
harshness of the tungsten flux was somewhat reduced in this way.
The wide variations in density of shadowgraph films obtained
from the several systems with identical exposures served to em-
phasize the effect of color modification in those systems depend-
ing largely upon ceiling and wall reflections.
Accuracy of Data. — The usual ratios between the maximum,
mean, and minimum illumination values observed on the 30-inch
plane are shown in columns 5, 6, and 7 of Table I. It will be
noted that these are given only to two places of significant figures,
and the authors wish to call especial attention to the desirability of
thus reducing the pretension to accuracy found in many illumin-
ating data. The maximum or minimum ratio is based on a few
readings at a single station and any extended experience with
the portable photometers at present available will convince the
tester that there is little probability of such value having an error
less than 5 per cent, while even in careful work errors of 10 per
cent, at a single station frequently occur. Furthermore in the
present state of lighting a 10 per cent, variation in the uniformity
ratios or indeed in such characteristics as mean intensity or specific
brightness have a negligible effect on the excellence of the in-
stallation and cannot be appreciated by the most experienced en-
gineer. Two places of figures thus generally carry the result
beyond the point of uncertainty, and give more than adequate
numerical precision.
696 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Uniformity of Intensity. — The uniformity produced on the 30-
inch plane by the five systems under consideration appeared
largely independent of the system used, being chiefly determined
by the spacing and suspension height. In the direct system using
six units mounted at the ceiling the maximum intensity was but
10 per cent, above and the minimum 20 per cent, below the mean.
With the indirect and dense semi-direct systems the maximum
was 20 per cent, above the mean and the minimum 30 per cent,
below it. This last variation was not considered excessive, a
high mean value assuring sufficient illumination at all points.
Utilisation Efficiency. — The utilization efficiencies obtained are
given in column 10, Table I. Those for the direct lighting sys-
tems are open to some question on account of the necessity, noted
in Appendix I, of assuming the flux generated by the lamps be-
fore they were bowl frosted; but as the means of six units are
believed to be fairly reliable. The figures for the semi-direct and
indirect systems were computed from flux values based on actual
photometric measurements and should have high accuracy.
The unusually high mounting of the direct units adopted in
an attempt to decrease glare and shadow, reduced the efficiency
of the direct systems, while the exceptionally low absorption of
the ceiling and walls greatly increased the efficiency of the semi-
direct and indirect systems as compared with similar tests made
in other offices.
With the possible exception of the indirect system, there was
not sufficient difference in the efficiencies found to influence the
final choice. Indeed utilization efficiency is believed to be of far
less importance with the higher-efficiency lamps and if the losses
of generated flux are expended to secure better diffusion or pre-
ferred color, the increased effectiveness may largely overbalance
the cost of absorption.
General Conclusion from Preliminary Tests. — The superiority
of the semi-direct and indirect systems over the direct in lessened
eye fatigue and in harsh shadow elimination seemed to the light-
ing committee to greatly overbalance the decreased utilization
efficiency, lessened uniformity and increased investment costs of
these more diffusing systems. As between the semi-direct and
indirect system, the advertising value of a visible light source in
DURGIN AND JACKSON: SEMI-DIRECT OFFICE LIGHTING 697
the offices of a company supplying light, a more ready control of
flux color and shadow density, and a somewhat higher utilization
efficiency led to the recommendation of the semi-direct system,
with the provision that semi-direct and indirect units of closely
similar design should be developed and that each department head
should decide which was to be installed in the offices under his
direction. This parallel design was carried out and the indirect
system chosen for the drafting room, where all agreed that the
minimum glare on tracing cloth made it ideal, and for about
5 per cent, of the offices. This represents such a small part of
the total floor area, however, that no further consideration is
given the indirect system in the present paper.
SEMI-DIRECT LIGHTING REQUIREMENTS.
The necessary characteristics of a satisfactory semi-direct
unit were considered to be: (a) Bowl brightness not more than
three times that of the ceiling, (b) Reasonably high overall ef-
ficiency. Hence a high reflection coefficient for the bowl interior
and little interference from fixture structure, (c) Color modifi-
cation of tungsten flux to a warmer tone, (d) Easy cleaning of
bowl and lamps.
Choice of Bowl. — The first requirement, moderate brightness
of bowl, served to eliminate a large proportion of the glassware
on the market. Twelve types of bowls submitted by eight manu-
facturers were equipped with three 100-watt lamps each and hung
30 in. (76 cm.) from the ceiling on 14 ft. (4.3 m.) centers in a
long office some n ft. (3.4 m.) in height. An indirect fixture,
similarly equipped and hung produced a maximum ceiling bright-
ness, viewed from a point directly below, of 80 millilamberts.
Assuming, as seemed highly probable, that no semi-direct equip-
ment could produce higher ceiling brightness under these con-
ditions, the desirable bowl brightness was limited to 240 milli-
lamberts. The average brightness of the bottom of twelve bowls
tested was 1,170 millilamberts viewed from below, and the aver-
age side brightness at the 8o° angle was 340 millilamberts. One
bowl of a widely used glass had a bottom brightness of 4,600
millilamberts and several a side brightness of over 500 milli-
lamberts. Frequently such excessive values were caused by the
shape of the bowl placing the glass too near the lamps when their
698 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
position was adjusted to bring the bulbs below the top plane of
the fixture ring; but it is believed that in addition to too shallow
bowl shapes at least 90 per cent, of the glassware now offered
for semi-direct use has much too high transmission.
The bowl finally chosen2 met all the requirements satisfactorily.
The bottom was about 2.7 times as bright as the brightest spot in
the ceiling and the side of practically ceiling brightness. The
depth, 6y2 in. (16.5 cm.) for a 20 in. (51 cm.) bowl and 5% in.
(13.3 cm.) for the 16 in (41 cm.) size, conduced to this result;
but the density of the triple-cased glass used was the principal
factor. Measurements made in the office shown in Fig. 4 gave
the values of Table II.
TABLE II.— Brightness Values in Office Equipped with
Eight Semi-Direct Units.
Millilamberts
Mean Maximum
Bottom of bowl 150 190
Side of bowl 60 90
Ceiling above bowl 55 60
Ceiling at center of four unit square 1.2 1.4
Ceiling at middle of side of four unit square 2.8 3.0
Side wall 6 ft. from floor 2.6 2.6
Side wall 4 ft. from floor 1.8 2.2
In so far as the glassware determined the efficiency of the unit
the chosen bowl seemed exceptionally good, the interior surface
being of pure white highly glazed and the regular and simple
curve (see Fig 2), giving a moderately wide distribution. The
cased glass permitted the toning of the transmitted flux to an
amber of approximate visual color match to that produced by a
metallized filament lamp at 96 per cent, rated voltage, while the
bowl retained when not lighted an appearance of iridescent white.
With the spectroscope this glass was found to absorb in trans-
mission all the tungsten lamp spectrum above the blue-green, but
in reflection from the interior surface the spectral composition was
entirely unaffected. The high interior glaze was recognized also
as of marked advantage for easy cleaning.
GLASS AND FIXTURE SPECIFICATIONS.
Purchase of Glassware on Specification. — To secure reasonable
uniformity in separate shipments of some 700 bowls when color
2 Calcite.
DURGIN AND JACKSON : SEMI-DIRECT OFFICE LIGHTING 699
and brightness were of paramount importance, it appeared neces-
sary to closely specify these qualities. Previous practise offered
no published precedent and in consequence the specification
shown in Appendix II was proposed and submitted to the manu-
facturer. This is presented not as a finished solution of the ques-
tion, but as a focus for discussion of a seemingly neglected means
for improvement of lighting practise. Even after conscientious
inspection of each bowl by the manufacturer for compliance with
the specification, the customer's inspector rejected 2.5 per cent,
of the shipped bowls for size and 6.5 per cent, for uniformity of
color. Without specification then, no approach to uniformity
could be expected. Experience in this instance showed the glass
manufacturer more than willing to cooperate in the effort to
secure better product and although the rather narrow limits im-
posed lead to a very considerable number of rejections before
shipment, both parties are convinced of the benefit of the plan.
The expense to the customer of carefully inspecting each bowl
for fit in a gauge ring, design, dimensions and quality of etching,
for appearance when lighted with lamps grouped as in the com-
pleted unit, and for color tone as compared with a bowl selected
as standard was less than 7 cents per bowl.
Fixture Design. — The principal desiderata in the fixture were
an effect of substantial and simple design, small interference with
generated light flux, and the inclusion of a double ring to permit
easy cleaning. In the specification given to the various fixture
houses the last feature was covered by the following statement :
"The scheme consists of a double ring, one ring to be stationary and
to carry the socket equipment, the other securely hinged to the first, to
be so arranged as to be dropped easily at one side for allowing ready
accesss to the interior of the bowl for cleaning. The hinge must be at
least 2 inches wide and of sufficient strength to carry bowl weight with-
out wear. Means for locking the two rings together must be provided at
a point diametrically opposite from the hinge, the locking scheme to
permit quick separation of the bowls but to be of ample strength to
support bowl weight. Means for securing the glass bowl in the lower
ring easily and permanently also must be arranged. The design of the
two rings should provide a rabbet or other overlap between them so that
no leakage of light is possible."
The accepted realization of these ideas is well shown in Fig. 2,
a and b. Two strap-iron rings are arranged to fit concentrically.
7
yOO TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
The outer ring carries a brass spinning to give the exterior finish
and provide a lip for supporting the bowl, while the inner ring
carries the lamp sockets and is in turn carried by the four sup-
porting rods. Two of the three clips arranged to retain the bowl
are shown in b, and the spring catch which holds the rings
together may also be seen at the lowest point of the outer ring.
This arrangement permits the bowl to be lowered in a few sec-
onds, exposing both sides of the lamps for dusting and permitting
the interior to be cleaned with a single sweep of a cloth. The
entire dusting operation can be performed in less than two
minutes.
Especial attention was given to lamp position, the socket loca-
tion being specified by the resulting position of the lamp tips as
shown in Fig. 6. This figure also shows the details of canopy
employed. The particular point to be noted here is the iron
bridge which carries the stress from the rod rings to the central
hickey and by means of a nipple and lock nut supports the
fixture when the canopy shell is removed, thus permitting the
connection of wiring after the fixture is permanently in place.
This construction was suggested by the manufacturer and is in
more or less common use in fixtures, but is emphasized because
of its strength and convenience.
Each fixture was inspected after hanging, the lamp position
checked with the largest specified size of lamps and, where neces-
sary, altered under the inspector's direction to give a uniform
illumination of the entire bowl. As will be noted from the dimen-
sions given in Fig. 6, the lamps were placed higher in the bowl
than usual. This arrangement gives a breadth of distribution
leading to a bright band on the upper part of the side wall if the
unit is installed less than 6 feet from the wall, but is necessary,
even with such deep bowls, if each bowl is to have that even
gradation of brightness and freedom from spotting which is
believed to be one of the most pleasing details of a good semi-
direct unit.
Characteristics of Complete Unit. — The average 20 in. (51 cm.)
bowl weighed 9 pounds and the efficiency of the unit was found
to increase slightly for lighter and decrease for heavier bowls
due to corresponding variations in transmitted flux. These varia-
Fig. 2.— (a) Standard semi-direct unit: (b) 20-in. bowl opened for cleaning.
Fig. 3. — Shadowgraph apparatus.
Fig. 4.— Typical Commonwealth Edison Co. office lighted by eight
semi-direct units on 14 feet centers.
Fig. 5. — Office of Fig. 4. with units converted to an indirect system.
DURGIN AND JACKSON : SEMI-DIRECT OFFICE LIGHTING 701
tions, however, were not more than 1.5 per cent, from the mean
unit efficiency of 80 per cent. A standard fixture equipped with
a bowl weighing 8.7 pounds and three 100-watt tungsten lamps
gave the distribution curves shown in Fig. 7, and summarized in
Table III.
TABLE III.— Distribution from Semi-Direct Unit.
lumens Per cent.
Generated flux 2,875 100
Absorbed by fixture 15 0.5
Distributed by fixture without bowl in
lower hemisphere 1,525 53
Distributed by complete unit 2,330 81
Portion of complete unit flux, in lower
hemisphere 260 1 1
Portion of complete unit flux, between
1050 and 1800 1.930 83
Curve B of Fig. 7 is of especial interest as it indicates the pre-
ponderance of flux in the lower hemisphere from the bare lamps
caused by the downward tip of the bulb axes and the slight ab-
sorption from the fixture structure. Such absorption was re-
duced to a minimum by covering the interior of the fixture rings
with aluminum paint and by the comparatively light supporting
members employed. Photometer readings at 1700 and 1800
could not be obtained with the apparatus available, hence curve
A was extrapolated for these points as indicated by broken line.
This procedure should introduce a negligible error in the flux
values as the zones affected are of small area.
In curve C the portion of curve A from o° to 900 is redrawn
at an enlargement of five times to show the intensive character
of the distribution in the lower hemisphere.
COMPLETED OFFICE INSTALLATIONS.
The office floors of the Edison Building are arranged on three
sides of an oblong court 60 by 120 ft. (18 by 37 m.) in extent and
a central corridor divides a considerable part of each floor into
an inner and outer space. This arrangement leads to three
groups of offices approximating 20, 30 and 56 ft. (6, 9 and 17 m.)
in width, many of the general clerical spaces being comparatively
long while the private offices average 15 ft. (5 m.) square. The
ceiling height varies from 10 ft. 1 in. (3.1 m.) to 17 ft. 3 in.
702 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
(5.3 m.), 44,000 sq. ft. (4,100 sq. m.) or nearly 54 per cent, of the
total floor area having a height of 10 ft. 9 in. (3.3 m.).
The considerable range in width of offices necessitated a
similar variation in the spacing of the semi-direct units. 14 ft.
(4.3 m.) between centers was taken as the maximum and this
distance may be considered standard, although spacings as low
as 8 ft. (2.4 m.) were used in a few cases. In general the shorter
spacings were employed in private offices and units with 16-in.
(41 cm.) bowls installed carrying two or three 60 or 100- watt
tungsten lamps.
The complete system of offices required 250 of these 16-in.
(41 cm.) bowl units, while 450 of the larger units equipped with
20-in. (51 cm.) bowls were used. Most of these carry three
100- watt tungsten lamps, but in a few instances 60- watt or 150-
watt lamps are necessary to produce the standard mean intensity.
All offices were decorated with the cream and brown tints of
calcimine described for the test room and after six months of
use the reflection coefficients were found to be about 0.8 for the
ceilings and somewhat above 0.7 for the walls.
Taking an office width of 28 ft. (8.5 m.), a ceiling height of
10 ft. 9 in. (3.3 m.), a spacing distance of 14 ft. (4.3 m.) and
the larger or 20-in. (51 cm.) bowl unit with the upper edge of
ring 30 in. (76 cm.) from the ceiling as representative of the in-
stallations, complete illumination tests under these conditions
were made in two rooms, one 50 ft. (15 m.) and the other 100 ft.
(30 m.) in length. The results check so closely that all data
have been averaged together and are here presented as applying
to any of the group of long offices having the stated width and
height. The end-wall effect is to decrease the average illumina-
tion about 10 per cent, in a strip extending some 8 ft. (2.4 m.)
from the wall and in offices approaching a square plan this affects
the mean values to a small extent but in the longer offices is
practically negligible. End walls, therefore, are neglected in the
following discussion and the computations based on intensities
obtained in the middle half of the rooms.
Illumination Tests. — To insure accuracy, checks were made
simultaneously by two observers using separate Sharp-Millar pho-
tometers, one of standard and the other of small size. In those
DURGIN AND JACKSON : SEMI-DIRECT OFElCE LIGHTING 703
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704 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
cases where results failed to agree the data were rejected or only
those used from the instrument showing no change on recalibra-
tion. In this way it was possible to obtain mean values differing
by less than 1 per cent.
The unavoidable variation in system pressure was met by
taking readings from side-wall sockets directly on the distributing
wiring, correcting for the measured drop to the fixture sockets
and further correcting to a standard mean pressure of 113 volts.
As there was some question of the relation between the intensity
of the amber filtered flux and pressure, an extended series of
readings was taken at five typical stations at five pressures rang-
Fig. 7.— Distribution from 300-watt semi-direct unit. {A) Curve when equipped with 20-
in. bowl. (B) Curve when equipped with lamps but no bowl. (3) Portion of (A) from
o° to 900, enlarged five times.
ing from 108 to 117 volts. These data were obtained for both
the total semi-direct flux and for the indirect component, but
when plotted showed an extreme divergence of only 1 per cent,
from the accepted curves for tungsten lamps. The removal of
the blue rays, therefore, has no appreciable effect upon the estab-
lished flux-pressure relations.
In Figs. 4 and 5 two views are presented of the office which
is 50 ft. (15 m.) in length. This room is equipped with eight
units and Fig. 4 gives a close representation of the lively char-
acter of the illumination, of the moderate brightness of the
DURGIN AND JACKSON: SEMI-DIRECT OFFICE LIGHTING 705
bowls, and of the absence of dense shadows. Fig. 5 presents the
method used for separating the indirect component for meas-
urement and suggests faintly the resulting flat appearance of the
lighting. The oil cloth covers drawn over the bowls to shut off
the direct component were grayish white on the outside and dull
black on the inside thus producing minimum interference with
the normal conditions of reflection from the bowl surfaces.
Summarized results from all illumination tests on clean bowls
and new lamps are given in Table IV. The mean semi-direct in-
tensity of 6.0 foot-candles on the 30-in. (76 cm.) plane corres-
ponds to a utilization efficiency of 42.5 per cent, with 115-volt,
i-w. p. c. lamps operated at 113 volts, a flux of 2,770 lumens
applying to an area 14 ft. (4.3 m.) square. The corresponding
mean indirect intensity of 4.9 foot-candles, or a utilization ef-
ficiency of 35 per cent, is not far below that obtainable with the
best indirect units and indicates the excellence of the interior
finish and shape of the bowls.
TABLE IV.— Illumination Values from Completed Semi-Direct
Installation.
Intensities in foot-candles Uniformity ratio
on 30 in. plane , < ,
/ " > Max. Max. Min.
Max. Mean Min. Min. Mean Mean
Semi-direct 8.0 6.0 4.2 1.9 1.3 0.7
Indirect 5.6 4.9 3.7 1.5 1.1 0.8
Direct 2.8 1.1 0.7 4.0 2.5 0.6
The mean semi-direct illumination thus contains a direct
component of 18 per cent., which although it is somewhat higher
than the 12 to 15 per cent, advocated on theoretical grounds,2
appears eminently satisfactory in affording a restful contrast and
minimum eye fatigue. It should be noted that this 18 per cent,
of illumination is given by 11 per cent, of the generated flux.
In Fig. 8 the relation of the three components are shown, the
lower group of curves giving the relative intensities across the
room on a line 30 in. (76 cm.) above the floor directly under the
units, and the upper group, similar intensities midway between
2 Symposium on Indirect, Semi-Indirect and Direct Lighting: Trans. I. E. S., vol.
VII, p. 234; 1912.
706 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
two such lines of units. The semi-direct intensity immediately
beneath the bowl is taken as unity and all other intensities plotted
in percentage of this value. Perhaps the uniformity of the in-
direct component and effect of the direct component in relieving
the flatness are the most notable points indicated. The drop in
intensity toward the side walls is also well shown. This pro-
duces a considerable decrease in the mean intensity and since
many of the desks are placed toward the center line of these long
offices, it may be fairly stated that an intensity of 7 foot-candles
under clean units is being used by a majority of the clerks in
1 1 1
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to total flux on a 30 in. plane.
these rooms. Allowing 20 per cent, decrease before cleaning,
the average value of the intensity for these desks is approximately
6 foot-candles. Wall brightness within the ordinary field of
view as noted in Table II reaches values more than one-third those
produced on matt paper under a 6 foot-candle illumination and
would seem to be too high for best eye efficiency. As yet, how-
ever, no complaints of this condition have been received, due
perhaps to the fact that a large part of the wall is covered by
dark mahogany cases and that these high brightness values only
apply to small areas where structural limitations have brought
units close to an end wall. The greater part of the wall has z
brightness about one fourth that of mat paper on the desks.
DURGIN AND JACKSON : SEMI-DIRECT OFFICE LIGHTING 70J
Dust Factor. — Extra care was used in securing the data for
the dust deterioration curve, Fig. 9, and the plotted points from
three locations representing the most dusty offices in the building
show no departure from a straight-line law during the observation
period of three weeks. As the absorption had increased to 25
per cent, at that time the further performance was considered of
little interest. A bi-monthly cleaning schedule will insure an il-
lumination at all times above 80 per cent, of the clean-bowl con-
dition. Such a schedule is being made effective and although
= 'C0
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WEEKS Or DUST ACCUMULATION
Fig. 9.— Dust absorption factor of standard C E. Co., semi-direct
office installations.
experience is not yet sufficient to permit accurate maintenance
cost figures, the fixture design bids fair to reduce cleaning ex-
pense to a very nominal amount.
CONCLUSION.
In the use of a mean intensity above 6 foot-candles and of a
distinctly amber tone of effective flux the office lighting in the
Edison Building of Chicago represents an experiment. There is
no question as to the immediate popularity of the results. Clerks
and department heads agree in commendation. But the element
of time is lacking as yet and only extended experience can show
whether high intensities and filtered flux will prove a permanent
advance.
The low value of bowl brightness and the fixture design em-
ployed are more confidently presented as realizations of generally
accepted but rarely applied principles and the dust deterioration
curve will give definiteness, it is hoped, to the much discussed
question of semi-direct lighting maintenance.
The accumulation of data for this paper has been possible only
through the cordial cooperation of Messrs. G. W. Baker and
R. E. Powell of the Commonwealth Edison testing department
and to them the authors tender their hearty thanks.
708 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
APPENDIX L— EQUIPMENT AND PROCEDURE FOR
PRELIMINARY TESTS.
Room. — Arranged as described in paper.
Wiring. — A system of metal moulding and outlets was installed
on the ceiling whereby a symmetrical 2, 4, 6, or 8 unit system
could be used. To insure accurate indication of the voltage ap-
plied to the lamps two pressure taps were arranged directly on
the ceiling wiring. Provision was also made for measuring the
current and installing a controlling rheostat at the switch cabinet.
Steadiness of Supply. — Recording voltmeter charts and fre-
quent readings with indicating voltmeter showed the day pressure
to be within -f- or — one volt of the mean value 112 volts. The
average during each test was computed from twenty readings
and the flux corrected to this value using National Electric Lamp
Association curve4 for variation of candlepower with pressure.
Lamps. — The lamp equipment comprised:
2 250-watt, iT4-volt clear bulb lamps assumed to give
standard average flux (2 x 2,450 lumens) at 114 volts.
4 150-watt, 116-volt clear bulb lamps photometered at 116
and 1 13.5 volts for m. h. cp. Flux computed using re-
duction factor of 0.785.
6 100- watt, 114-volt clear bulb lamps rated at 114 volts
for m. h. cp. and total flux by General Electric Co.
6 100-watt, 114-volt bowl frosted lamps assumed to gen-
erate standard average flux (908 lumens) at 114 volts
before frosting.
6 60-watt, 114-volt bowl frosted lamps assumed to gen-
erate standard average flux (526 lumens) at 114 volts
before frosting.
6 60-watt, 114-volt bowl frosted lamps photometered at
112 volts for m. h. cp. and flux computed using re-
duction factor of 0.785.
Glassware Equipment and Mounting Heights. —
1. Prismatic reflectors X-I 100, velvet finish used with
form H holder mounted at 9 ft. 9 in. (3m.) from the
floor to lower edge.
* Engineering Department, National Electric Light Association Bulletin 13C, p. 9;
February 1, 1913.
DURGIN AND JACKSON : SEMI-DIRECT OFFICE LIGHTING 709
2. Opal glass reflectors. Sudan No. 01213 8 in. (20 cm.),
Panalex design, dull finish used with form H holder.
Mounted 9 ft. 9 in. (3m.) from the floor to lower
edge.
3. Art glass. Monolux No. 3,540 and 3,541. Mounted at
8 ft. o in. (2.4 m.) from floor to upper edge.
4. Opal glass semi-indirect. Calla No. 1,215 J6 in. (41
cm.). Mounted 8 ft. o in. (2.4 m.) from floor to upper
edge.
5. Totally indirect. X-Ray No. 14,270 mounted at 8 ft
o in. (2.4 m.) from floor to upper edge.
Note. — XI 60 Prismatic and Sudan No. 01213 7 in. (18
cm.) reflectors were used with 60- watt bowl frosted
lamps suspended 9 in. (23 cm.) from ceiling for low
intensity direct system tests.
Bye Fatigue Tests. — A standing desk 6 ft. (1.8 m.) long by
3 ft. (0.9 m.) wide and having a mean height of 44 in. (1.1 m.)
was placed facing toward the center of the room, with stool in
position indicated. By arrangement an accountant of the treasury
department did regular accounting work, principally extensions
of books, under each of the five different schemes of illumina-
tion. His working day averaged about seven hours and he used
each system for five days. Before starting work and at the close
of work in both morning and afternoon periods, Ferree tests
were made on his eyesight by J. R. Cravath, giving two pairs of
tests per day or ten complete visual tests under each system.
Tests of Light Direction (Shadowgrams). — A new method
was developed for recording shadows photographically — shown
in Fig. 3. A plate holder loaded with Velox transparency film
was supported in a 30 in. (76 cm.) horizontal plane at the sta-
tion to be investigated, the lights turned off, the film exposed, a
round vertical rod 3/32 in. (2.3 mm.) in diameter and i1/2 in.
(3.8 cm.) long standing on circular base 3/8 m- (l cm0 in diam-
eter placed in the center of the film and the lights turned on for
30 seconds. Shadows thrown by the rod were recorded on the
film. One end of the film previously protected was later exposed
in the laboratory under fixed conditions, the tone of the print
7IO TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
from this end serving as a check to show that the chemical man-
ipulation of all films was identical.
Intensity Measurements. — Eighty stations were laid out mak-
ing each the center of a 28^ in. (73 cm.) square. As preliminary
surveys on a plane 30 in. {j6 cm.) above the floor showed the
four quarters of the room to be practically identical in horizontal
illumination, the final tests were confined to this plane and to the
twenty stations in a single quarter.
A Sharp-Millar photometer (standard size) was used exclu-
sively. It was mounted on truck for quick movement from sta-
tion to station, storage battery supply and ammeter reading being
used to insure constancy of comparison lamp. The instrument
was checked against standard lamp in the laboratory every two
or three days and showed fair performance.
In the actual surveys four readings were taken at each station
and the mean accepted as the actual value. A complete set of
eighty readings could be taken easily in one half hour.
APPENDIX II.— SPECIFICATION COVERING BOWLS
FOR SEMI-INDIRECT LIGHTING EQUIPMENT.
Quantity. — 20-inch bowls and 16-inch bowls
are to be furnished under this specification on Commonwealth
Edison Company purchase requisition No
Material. — Bowls are to be of special grade of
glass manufactured by the under the trade name,
Design. — Bowls are to be etched with special Greek fret and
central web as shown on sketch submitted by
The upper edge of Greek border is to be 2T/2 in. below bottom
edge of rim, and over-all width of border is to be 2^ in. on 20-in.
bowls. All measurements taken over the curving surface of the
bowl. Central web of 20-in. bowls to be 7% in. in diameter. All
three dimensions to be decreased proportionately for 16-in. bowls.
Etching Detail. — All etched lines to be smooth and of uniform
depth. Greek border to be strictly parallel to edge of bowl.
Variation in distance between support edge of bowl lip and upper
edge of Greek border to be not more than 1/16 in. in any given
bowl and variation of average distance between support edge of
bowl lip and upper edge of border of different bowls to be not
DURGIN AND JACKSON : SEMI-DIRECT OFFICE: LIGHTING 711
more than 1/8 in. Central web to be centered within 1/8 in. of
center of circle outlined by lower edge of Greek border.
Etching details to be checked by measurement and inspection
of a sample from each shipment comprising 5 per cent, of lot se-
lected at random.
Surface Finish. — External surface to present uniform irides-
cent texture, free from scratches, lines or other blemishes. In-
ternal surface to be highly polished, free from bubbles, bunches
or other irregularities.
Twenty-inch Bowls (1. Weight). — Weight of 20-in. bowls on
this order is to be within one pound of the average weight of the
lot, that is, no bowl more than one pound heavier or one pound
lighter than the average will be accepted. The limits of maximum
and minimum weight thus established shall apply to all future
orders for this style and size of bowl.
(2. Over-all Dimensions). — Each bowl to fit sample ring fur-
nished. Outer diameter of lip to be 20 in. plus or minus Via in-
(3. Thickness). — Thickness of any given bowl to be so uniform
as to permit even color tone over entire bowl when lighted by
three or four symmetrically placed 100- or 150-watt Mazda
lamps. Variation in average thickness of separate bowls to be
within limits necessary to give close color tone match to standard
bowl used to check previous shipments of 20-in. design
bowls.
(4. Inspection by Customer.) — Compliance of shipment with
weight specification to be checked by weighing all bowls. Com-
pliance with thickness specification to be checked by inspecting
uniformity of color of each bowl when lighted by three 100-watt
lamps, and by comparing this color with that of standard
bowl.
Sixteen-inch Bowls. — These bowls to be of quality
agreeing with the spirit of above specification for 20-in. bowls,
necessary modifications being made in proportion to reduction of
diameter.
(1. Weight). — Average to be specified after receipt of first
one dozen bowls.
(2. Over-all Dimensions). — Each bowl to fit sample ring fur-
nished.
712 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
(3. Thickness). — Thickness specification identical with that of
20-in. bowls except that 60- and 100-watt lamps shall be used.
(4. Inspection by Customer). — As outlined under 20-in. bowls.
Rejection of Imperfect Bowls. — If checks on samples as out-
lined above show breach of specification, entire shipment to be
checked for detail in question and all bowls not in strict com-
pliance with requirements to be rejected.
DISCUSSION.
Mr. F. A. Vaughn : I am anxious to utter a few words of
commendation for work of this kind, especially the reference to
the translucent bowls and the study of their characteristics and
the attempt to discover luminous bowls which will satisfactorily
meet the illuminating engineering requirements. This paper is
particularly valuable, not only in its technical results and the
highly satisfactory use of a particular type of glassware in a
specific office, but in pointing out, as the authors have done, the
almost utter lack of bowls which are satisfactory, if one wishes
to have a choice. The choice of the illuminating engineer is
undoubtedly restricted very greatly, in spite of the very great
number of different types of glassware presented to him. Most
of them are not satisfactory for this sort of work, and I hope that
investigations of this kind will spur manufacturers on to making
more dense, more esthetic and more beautiful glassware so that
we will not be so restricted in our choice of units of this character.
Mr. W. R. Moulton : The authors are to be commended for
the thoroughly practical data and information presented in this
paper. It is of special value to the practical engineer who is
daily confronted with similar problems.
The glass manufacturer is usually more interested in the pro-
duction of a great number of bowls at a certain profit, than in
the lighting result obtained from his glassware. This work in
Chicago has impressed this particular glass manufacturer with
the value of a complete study for the application of his product
to illumination problems. This experience will undoubtedly
improve his product in the future, and in turn assist in raising
the general standard of all the manufacturers.
Fixture construction is an item of sufficient importance to
SEMI-DIRECT OFFICE LIGHTING 713
merit the engineer's consideration. Cooperation of the engineer
with the fixture designer and manufacturer should result in a
greatly improved product, without sacrificing any artistic effect.
The work done by the authors proves this conclusively.
Mr. J. R. Cravath : You will notice that the authors have
given figures on the brightness of the bowls as compared with the
brightness of the backgrounds against which they are likely to
be seen. The care taken to keep those ratios low represent some
of the most important work done on this installation. In a
report that has already been filed with the Council by this year's
Committee on Glare, is the carefully considered statement that in
the opinion of the committee the evidence so far indicates that
contrasts of brightness in excess of from 1 to 100 to 1 to 200 are
likely to produce "glare," that is manifested by eye fatigue or
annoyance. You will notice that the figures given in the paper
are well within that range. A point not fully appreciated here-
tofore, which I would like to emphasize, is that it is not so much
the absolute value of the brightness of the globe as it is the
brightness compared with its background that causes glare.
I can second what Mr. Vaughn has said as to the difficulty of
getting sufficiently dense semi-indirect glassware. Most of the
semi-indirect installations heretofore have not been properly
engineered, if engineered at all. We need to give more attention
to this point, the brightness of our semi-indirect bowls.
Mr. R. ff. Pierce : This paper is a particularly interesting
one to me because, in the course of designing glassware fixtures
for a line of semi-indirect lighting units which the company I
am connected with placed upon the market about a year ago for
use in connection with horizontal Bunsen burners, we undertook
practically an investigation of the same considerations from a
purely commercial standpoint. Mr. Durgin and his co-author
have been fortunate, possibly, in that the results of their investi-
gations were not required to be passed upon and endorsed by the
general public, whereas the designs upon which we decided were
subjected to the approval of the purchasing public; in other
words, they were manufactured for sale, and in connection with
this two or three considerations of considerable interest arise.
It is noteworthy in the first respect that the design finally agreed
714 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
upon is substantially the same in both cases. We decided upon a
bowl for lighting which has substantially the same characteristics
of distribution as the one displayed here, but we found that the
general public demanded higher intensities, — higher brightness in
the bowl — than was exhibited in the glassware first used. In other
words, people have not succeeded in getting it out of their heads
that there is anything in illumination more important than getting
an extremely bright piece of glassware, and that has been the
greatest obstacle we have to overcome in raising the standard of
illumination in the trade which we sell. The general public de-
mand much higher bowl-brightness than are found to be satis-
factory to discriminating observers. We found, for example, that
those bowls which gave a brightness of four of five times and
eight and ten times the brightness which we had fixed upon, were
demanded by the majority of the consumers. The average con-
sumer seems to be obsessed with the idea that all that is necessary
to make a semi-indirect lighting fixture is a piece of glass more or
less opalescent turned upside down. In some previous papers pre-
sented to this society, Dr. Ferree presented the results of an in-
vestigation in which he showed that with orders of surface bright-
ness ranging above 0.1 candlepower per square inch, diffusing
glassware of any character whatever was practically no better
than a bare lamp, and with that in view, it appears to me that the
general, broad claim that any type of semi-indirect lighting repre-
sents an improvement over unshaded lamps is misleading. Prob-
ably the indirect lighting systems possess a degree of brightness
which makes them practically no better than bare lamps as far as
the fatigue of the eye is concerned, and I think that some con-
certed movement to limit the degree of brightness to something of
the order shown in this sample is highly desirable.
Mr. S. B. Burrows : There is one point in this paper which
appeals to those of us who are interested in kilo-watt-
hour sales as well as the application of the principles of il-
lumination, and that is the point that at the present time both the
central station and dealer talk in terms of candlepower.
It is no wonder that most of our customers are in the frame of
mind Mr. Pierce speaks of, for there are any number of jobbers
and electricians, in practically every town, selling gas-filled tung-
SEMI-DIRECT OFFICE UGHTING 715
sten units indiscriminately as lamps, rather than illumination,
neglecting accessories which would conform to or help the high
intrinsic brilliancy of the unit. There is a field here which, it
seems to me, for engineers is the biggest we have seen for some-
time, namely increasing lighting sales in kilowatt-hours by push-
ing the sale of glassware which is admittedly best for the eye,
thereby increasing the wattage in any one installation, and giving
better illumination.
Those of us who are not only illuminating engineers but also
salesmen should give more attention to the semi-indirect and indi-
rect fixtures than we have heretofore given, if for no other reason
than for those sales.
Mr. H. Thurston Owens: The sale of semi-indirect fix-
tures varies inversely with the size of the bowl. The smaller
bowls are cheaper to make and easier to sell, and as this condition
is at variance with the promotion of better lighting it will take the
concerted action of the whole lighting industry to change the situ-
ation. Many of the so-called semi-indirect units are, in effect, di-
rect lighting units and produce a glare quite as objectionable as
the older forms of direct lighting.
Mr. W. A. Durgin (In reply) : One point may bear
amplification. We advocate a dense amber bowl, not pri-
marily because it has high absorption and hence leads to the
sale of more energy. We advocate it because we believe
that the amber filtered flux gives the customer increased effective-
ness of lighting far more than in proportion to the decreased
utilization efficiency. The time has arrived when we can afford to
throw away a part of the generated flux in order to secure higher
effectiveness from the filtered remainder. The customer gets the
advantage of better lighting in increased business, increased pro-
duction, improved eye hygiene or esthetic satisfaction; the lamp
manufacturer sells larger lamps, the fixture and glassware people
sell semi-direct instead of small direct combinations and the cen-
tral station maintains output.
yi6 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
THE APPLICATION OF CROVA'S METHOD OF COL-
ORED LIGHT PHOTOMETRY TO MODERN
INCANDESCENT ILLUMINANTS.*
BY HERBERT E. IVES AND E- E. KINGSBURY.
Synopsis: Crova's method of colored light photometry, which con-
sists in the observation of the photometer field by monochromatic light
of a selected wave-length, is one of the simplest and most practical means
of facing the problem under those conditions where the method is
applicable. Practical means for applying the method are here developed
for the ordinary incandescent electric and gas illuminants. Calibrations
are made on the basis of the authors' luminosity scale.
Lord Rayleigh1 suggested in 1885 that the comparison of com-
pound lights of somewhat different color might be facilitated by
observing them by monochromatic light. He described a mono-
chromatic telescope to be used for this purpose. Crova,2 going
a step further, suggested that such a monochromatic color of the
spectrum be chosen so that the total luminous intensity of the
lights under comparison would be represented by their relative
intensity at this wave-length. He showed that, in the case of
illuminants possessing continuous spectra, such a representative
wave-length could be found.3
The advantages of the Crova method for eliminating color
differences in photometric comparison are very real, and it is at
first sight strange that it has not been more generally employed.
The reason is not far to seek, however. Like all other means for
eliminating color differences at the photometer, Crova's method
must be calibrated in terms of some accepted luminosity scale.
The ability to make a perfectly definite setting agreeing with the
setting of any other observer is, in the majority of cases, of no
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, T9i5-
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
1 Rayleigh, A Monochromatic Telescope, with Application to Photometry ; Phil. Mag.,
June, 1885.
2 Crova ; Comples Rendues, 93, p. 512.
3 Ives, Note on Crova's Method of Heterochromatic Photometry ; Physical Review
March, 1911.
IVES AND KINGSBURY: COLORED LIGHT PHOTOMETRY 717
value unless one knows what value to give to that setting. In
the case of Crova's method this means that one must have some
definite proof that the wave-length employed is the representa-
tive one or else know how much it over or under-evaluates the
intensity of those light sources which are of interest.
In searching for the most practical method of colored light
photometry for use in a gas photometric laboratory, we have
recently experimented with Crova's method with very satisfac-
tory results. The problems of gas mantle photometry are some-
what peculiar. There exists a wide range of color in mantles of
different composition and structure, added to which are smaller
differences caused by variations of adjustment of the burner and
by changes in the kind of gas used. These differences cannot be
taken care of by the mere change in concentration of a color-
matching solution, as in the case of the Fabry solutions as worked
out for the electrical illuminants.4
There are several different requirements to be met in the prac-
tical development of means for carrying out Crova's idea, which
are in partial conflict. The dominating practical requirement is
that the means for securing monochromatic light shall not be
prohibitively wasteful of light. This practically means that a
compromise must be made between the purity of the monochro-
matic light and the working illumination.
A second point, governed in part by the one just emphasized,
is that different parts of the spectrum are differently suited for
securing monochromatic light with maximum quantity. Thus,
the hue of the spectrum changes very rapidly in the yellow, so
that there a very narrow band must be chosen in order to elimi-
nate color differences. On the other hand, in the green region
hue change is slow, and a comparatively wide band of the spec-
trum may be used, with consequent increase of light. Finally
comes, of course, the restriction that the true representative or
Crova wave-length has no connection with the luminosity or hue
considerations. It actually happens that the Crova wave-length
lies in the yellow, where hue change is rapid. Thus there is as one
alternative working for the most complete elimination of color
difference, using a wave-length in the green, and determining its
• Ives and Kingsbury, Experiments with Colored Absorbing Solutions for Use in
Heterochromatic Photometry i Trans. I. E. S., p. 795, 1914.
718 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
calibration ; and as another alternative working for perfection of
color difference elimination in favor of the convenience of the
true Crova wave-length. Actually, as will be seen, still other
considerations have had a say in our particular problem.
To obtain monochromatic light Crova used a solution of nickel
nitrate and ferric chloride, placed between the eye and the photo-
meter. After some study of colored glasses we have decided in
favor of the use of a solution, similar in properties to the one
used by Crova, as being more definitely reproducible and as being
more nearly monochromatic. Our first work was done upon a
monochromatic green solution, which had been developed for
another purpose,5 our idea being that its excellent monochromatic
quality would outweigh its non-agreement with the Crova wave-
length. The transmission of this solution, whose composition is :
CuCl 265.0 grams
K2Cr207 2.5 grams
HN03(i.o5 gr.) 26.5 c.c.
Water to 1 liter of solution at 200 C.
was measured in a thickness of one centimeter, against a clear
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Fig. 1.— Transmission of monochromatic green solution with various illuminants, in
times of its transmission of the light of a "4-watt" carbon lamp.
water solution, by means of our physical photometer,6 which
incorporates the characteristics of our average eye. The results
with various illuminants, all expressed in terms of the standard
6 Ives and Kingsbury, Flicker Photometer Measurements by a Large Group of Ob-
servers on a Monochromatic Green Solution ; Physical Review, March, 1915, p. 230.
6 Ives and Kingsbury, Physical Photometry with a Thermopile Artificial Eye ;
Physical Review, 1915.
IVES AND KINGSBURY: COLORED LIGHT PHOTOMETRY 719
"4-watt" carbon lamp, are shown in Fig. 1. The abscissae are
watts per mean spherical candle, in the case of the electric lamps,
and proportion of ceria, in the case of the mantles, the mantles •
used being of a representative weave and weight.
For our purposes this solution was decided not to be suitable,
the chief reason being that the mantle values lie on a line which
is altogether too steep. While the values are given in terms of
mantle composition, the color is as well a matter of weight and
weave and of burner adjustment. Variations of any of these
factors, such as are to be expected in miscellaneous testing, were
found to be equivalent to running up and down on the curve by
an amount of several per cent.
Our experience with this solution led us to formulate a new
criterion for our own work in mantle photometry, namely, that
the monochromatic solution to use is one which has as nearly as
possible the same transmission for all the ordinary gas mantles,
irrespective of what it might be for other illuminants. We would
then be as free as possible from the effects of the variables
peculiar to that kind of photometry.
Using the physical photometer a process of trial and error was
gone through with the relative proportions of the two coloring
constituents of the solution being gradually changed so that the
equivalent wave-length moved toward the yellow. A solution was
finally obtained which answered to the requirements, whose com-
position is as follows :
CuCl2 90.0 grams
KjCrj07 30.0 grams
HNO3 (x-°5 Sr-) 4°° c-c-
Water to 1 liter of solution at 200 C.
This solution is to be used in a thickness of 25 millimeters.
A calibration of this solution was carried through with the
physical photometer, not only for the mantles but for all the
common electric and flame illuminants. This calibration is shown
in Fig. 2, by the crosses.
Supplementary to this a partial calibration was made by the
visual methods developed by us ; for while we have established
the agreement of the visual and physical methods with great care
it was thought worth while to take this opportunity to make a
further check. We first made a set of observations by the flicker
720 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
method, under the standard conditions, selecting our observers
according to the scheme recently described before the Society.7
The procedure was to have each observer make a set of readings
with an ordinary Lummer-Brodhun head, interposing the Crova
solution between eye and eye-piece. The eye-piece was then
1.10
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Fig. 2.— Transmission of Crova solutions in times of transmission with "4-watt'
lamp. Upper— gas solution ; lower— electric solution.
removed and the nicker photometer attachment8 put in its place,
and another set of readings made. Both sets were made against
a "4-watt" lamp. Under these conditions all questions of the
slight change of transmission of the solution with temperature,
etc., are ruled out. The flicker photometer points are shown by
dots.
In addition to the flicker settings a check was made upon the
electric illuminants by the use of the Fabry yellow solution
recently described,9 whose calibration was done by the same flicker
method, but by a different group of observers. The values
1 Ives and Kingsbury, On the Choice of a Group of Observers for Heterochromatic
Measurements; Trans. I. E. S., No. 3, p. 203, 1915.
8 Kingsbury, E. F., A Flicker Photometer Attachment for the Lummer-Brodhun
Photometer Head; Journal of the Franklin Institute, August, 1915.
9 Ives and Kingsbury, Experiments with Colored Absorbing Solutions for Use in
Heterochromatic Photometry, Trans. I. E. S., p. 795, 1914.
IVES AND KINGSBURY: COLORED EIGHT PHOTOMETRY J2I
assigned to the Crova solution by the Fabry solution are shown by
the circles.
It is evident that our various means of calibration are in excel-
lent agreement, and that we have a solution meeting our criterion,
that the incandescent gas mantles should measure alike.
Upon the completion of the work on the mantle solution, it
seemed worth while to determine what solution would answer the
same purpose for the incandescent electric illuminants. By a
slight change of the relative proportions of the constituents such
a solution was found, as follows :
CuCl2 86 grains
K2Cr207 60 grams
HNO3 ( 1.05 gr.) 40 c.c.
Water to 1 liter of solution at 200 C.
The calibration of this solution was carried out entirely with
THREADED RINGn^
GLASS-
Fig. 3. — Cell for holding Crova solution.
the aid of the Fabry yellow solution. It is shown in Fig. 2
(lower diagram). The transmission is practically the same over
the whole range of lamp colors from the color of the pentane
flame to that of the high efficiency nitrogen-filled tungsten.
For the practical use of these solutions we have devised a small
absorption cell which slips into the eye-piece of the Lummer-
Brodhun photometer head. It is shown in section in Fig. 3. The
solution is held in a glass cell consisting of a section of glass
tubing on which plane glass ends are fastened with paraffin. This
cell is then imbedded in the brass casing with plaster of Paris,
the excess being squeezed out when the threaded ring is screwed
into place. We have thus far had no trouble with any leakage
from these cells.
The procedure in using the solutions is quite simple. In our
laboratory the gas solution is of course used, except in special
work. Every photometer head is permanently equipped with its
722 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
solution cell. All the standard lamps have their efficiencies tabu-
lated on a card near the photometer, beside which is a blue-print
of Fig. 2. The operations are exactly as in ordinary photometry,
but the resultant values are to be reduced in accordance with the
ratio indicated by the chart. We have, however, introduced a
still further simplification by tabulating the "Crova solution
value" of each standard, which is simply the value to be assigned
to it in order that the readings on the mantles shall be in their
correct values as obtained. The Crova value of a 4.85 w. p. s. c. p.
carbon standard, for instance, is — — X its true value.
1.065
In the case of the electric solution no correcting values are
necessary; observations are made and recorded as though no
solution were present. Its use is, however, restricted to incan-
descent electric illuminants.
Our experience thus far with this method has been very satis-
factory. The very slight color difference which remains we find
to give no trouble, while the loss of light (the transmission is
about 10 per cent.) is taken care of by more careful shielding of
the observer's eye, and taking greater care to avoid looking at
the light source. The precision of setting is practically the same
as in ordinary photometry of lights of the same color. The
greater convenience of this method over those requiring a change
of absorbing medium with each change of illuminant makes it by
far the most practical laboratory means for eliminating color
differences.
The calibrations here given are in terms of the luminosity scale
developed and used in our laboratory. Should any other con-
sistent scale be ultimately adopted, slight changes in the relative
proportions of the constituents of these solutions would fit them
to perform the same function in conformity with such scale.
Fig. 4 shows the spectral transmission of the two solutions, and
in Fig. 5 these same transmissions are shown multiplied by the
energy distribution of a tungsten lamp and by the luminosity
curve of the eye. The resultant curves show (by calculations of
their centers of gravity) that the equivalent wave-lengths are
approximately 0.573/* for the mantle, and 0.577/i for the elec-
tric solution.
IVES AND KINGSBURY: COLORED LIGHT PHOTOMETRY 723
While we. have obtained our monochromatic light by the use
of absorbing media it is worthy of note that a very elegant method
would be by the use of a spectroscopic eye-piece, similar in prin-
ciple to Lord Rayleigh's monochromatic telescope, to take the
place of the ordinary photometer eye-piece. Such a device would
permit the variation of the wave-length used and also, by vary-
ing the width of the slit, of the amount of light, to suit the con-
I
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Fig. 5.— Spectral transmission of Crova solutions, multiplied by typical illuminant
energy distribution and visual luminosity curve.
ditions. The calibration of this kind of instrument could not be
done at present with the physical photometer, which would not be
sensitive enough, but the alternation of the flicker attachment and
a spectroscopic attachment in the manner described in connection
with the Crova solution, furnishes an excellent means for cali-
brating such an eye-piece. It, of course, involves the use of a
group of observers, but with the equivalent wave-length closely
determined by the present work, the labor of finding this exactly
should not be great.
724 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
DISCUSSION.
Dr. P. G. Nutting : If it is in order, I would like to ask a few
questions about the method rather than the matter presented here.
Do I understand, Dr. Ives, that you are entirely independent of
the observer? Are your intensities read as deflections of a gal-
vanometer needle ? I should also like to ask what the sensibility
of the method is, the amount of probable error, etc ; what is the
range over which it is applicable under the conditions described?
Dr. C. E. K. MeES : I should like to ask Dr. Ives what the sta-
bility of the solution is, and what means he takes to check it. It
strikes one who has been trained as a chemist, off hand, that a bi-
chromate and nitric acid would form a powerfully oxidizing solu-
tion, and if there is any possibility of its oxidizing anything it will
do it ; so it would be necessary to obtain some analytical check on
the solution.
M. Luckiesh : I should like to ask Dr. Ives if he has had an
opportunity to test the permanency of this solution over a period
of a few months or more. If it is permanent it will be of consid-
erable advantage.
Dr. H. E. Ives: Regarding stability, — strictly speaking, the
answer depends upon the time more than upon any definite evi-
dence we can offer. We simply say this, that the constituents
were the same as ones used in a previously developed solution,
on which many tests for permanency were made, and that during
the time that this work was continued, we watched very carefully
and made photometric checks of one sort and another which
would, we believe, have revealed any change in composition or
behavior. Now if you will note, from the figure showing the con-
struction of the containing cell, the solution is in contact with
nothing except glass, with the possibility of a very thin edge of
paraffin, so that the possibility of its doing any oxidizing is
negligible. The cells have not shown any leakage. I think
now it is about four or five months since our set of tanks was put
in use. We very recently made a check of the results obtained by
their use, against our physical photometer, and the check was ab-
solute. We have noticed some temperature coefficient of change
of transmission, and thought we noticed some reversible photo-
chemical change. For instance, we did part of the work with
COLORED LIGHT PHOTOMETRY 725
large tanks which were exposed directly to radiation from the
light source. We obtained some results which seemed to indi-
cate that if this solution were exposed to light continuously for a
long time, its transmission would alter somewhat. On being let
alone in the dark for a few hours, the solution returned to its
original state. In all the later work the solution was used ex-
clusively in the eyepiece, where the intensity of incident radiation
is very small, and any change would effect both sides of the field
practically the same.
Mr. Mees : Does it get yellower ?
Dr. Ives: Yes, it probably did. I do not remember exactly,
but all these changes which we have suspected are minimized in
their action by the method of use. If there is a change in the
total transmission without a shift, both illuminants are affected
equally. If there were a very large shift, that would be serious,
but we have not found any. I realize that this is not an adequate
answer to the general question of stability. If we had had these
in use for two or three years, we could, of course, give more
definite information, but I will say that we have found them
satisfactory and perfectly consistent with such checks as we have
made by going around the complete circle at various periods.
In regard to Dr. Nutting's question, whether the method is in-
dependent of the observer — of course, if we had an absolutely
monochromatic solution or used a spectroscopic attachment with
a sufficiently narrow band of transmission, we would be quite in-
dependent of the observer. (The transmission of a solution
much more monochromatic than the one described would prob-
ably be prohibitively low.) On a recent test of some incandescent
lamps which I mentioned a minute ago, in abstracting the paper,
we deliberately chose two observers from our laboratory, one of
whom I think is the most blue sensitive of any we have, and a
rather red sensitive one. These two observers made the observa-
tion and there were no systematic differences of any sort. I think
I am justified in saying that unless a very abnormal observer is
used, the method is independent of the observer.
Dr. P. G. Nutting : You do measure light rather than energy.
Dr. Ives : Yes ; this is a visual method. Now as to precision :
using the photometer as we do writh laboratory voltmeters, and
726 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
as a common battery we are working to probably less precision
than that of a laboratory such as the Bureau of Standards, where
they may have a whole storage battery for one particular investi-
gation, and it is very probable that the effect of even the slight
color difference still present would show itself on a long series of
tests in somewhat lower precision. But for our purposes, the
precision is all that could be desired. The range of applicability
is just so far as shown on these curves. It may be further, but we
do not so state.
SHARP AND LITTLE: COMPENSATED TEST-PLATE 727
COMPENSATED TEST-PLATE FOR ILLUMINATION
PHOTOMETERS.*
BY CLAYTON H. SHARP AND W. F. LITTLE.
Synopsis: The errors of illumination test-plates due to their devia-
tion from the theoretical cosine law have been studied experimentally
(Tables I, II, III, IV, Figs. 1 and 2). The most important cause for the
deviation of test-plates from the cosine law is shown to be the increasing
reflection with increasing incidence according to Fresnel's law (Fig. 3).
Test-plates may be compensated for the deficiency in brightness with
light at large angles of incidence by admitting light to the posterior side
of the plate in sufficient quantities. Transmitting test-plates are mounted
on flashed opal rings of suitable width and light at 900 is cut off by
a metal screen (Figs. 4 and 5). Reflecting test-plates are constructed as
in Fig. 6. The results of this method of compensating plates are shown
in Tables V and VI and are summarized in Fig. 7. The results of a
test of illumination with compensated and uncompensated test-plates are
given in Table VII. The possible application to the integrating sphere is
noted.
The only essential difference between a photometer for the
measurement of illumination and a photometer for the measure-
ment of candlepower is that the illumination photometer is pro-
vided with a photometric surface or test-plate which should vary-
in brightness as the cosine of the angle of incident light. The
test-plate, which serves as a device for integrating the luminous
flux falling upon it, is the distinguishing feature of the illumin-
ation photometer. Any failure on the part of the test-plate to
integrate correctly is reflected in corresponding errors in the re-
sults of the illumination measurements. This paper contains a
discussion of errors encountered in existing forms of test-plates
due to departure from Lambert's cosine law, and a description
of a method of compensating the test-plates in order to avoid
such error.
Classification of Test-plates. — Test-plates may be divided into
two general classes according to the method of their use :
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, I9I5-
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
728 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
(a) Transmitting (usually attached to the photometer).
(b) Reflecting (usually detached from the photometer).
Transmitting plates are made of diffusing glass usually de-
polished on the exposed surface. Reflecting plates may be of
opaque material having a diffusing surface, or they also may be
of depolished white glass.
Historical. — Unfortunately there is no known substance nor
method of constructing a surface which obeys the theoretical
cosine law of Lambert. Wright, some fifteen years ago, suc-
ceeded in making surfaces of compressed powders which came
very near it; but evidently this form of construction would not
lend itself to the practical requirements of photometry. There-
fore photometrists in measuring illumination have been obliged
to content themselves with test-plates which were known to give
erroneous results under conditions of high angle of incidence.
The comforting thought, however, was always present that prob-
ably in the great majority of cases the light flux incident at high
angles represented so small a percentage of the total flux that an
error in measuring it was relatively of little consequence. Never-
theless, the test-plate error has been by all means the largest in-
trinsic or unavoidable error in illumination measurements, and
the knowledge of its existence has been a thorn in the flesh of
photometrists. Therefore no little study has been given to the
question of a practical method of its avoidance.
The idea of replacing a material surface by an imaginary one,
such as a clear aperture in an opaque body, undoubtedly has
occurred to more than one worker in this field. Such an aperture
would evidently transmit light in accordance with the cosine law,
but unfortunately it would require some auxiliary arrangement
to diffuse this light. A small aperture in the surface of an in-
tegrating sphere would admit flux of light proportional to the
cosine of the angle of incidence, and the flux density at a point
in the interior of the sphere, which is shielded from the aperture,
would measure the flux admitted. Evidently such an arrange-
ment must have its limitations in practise, because of the prac-
tical limits of the size of the sphere and because the loss of light
involved in the multiple reflections required in diffusing the light,
will be so great that the field viewed in the photometer will be of
SHARP AND LITTLE: COMPENSATED TEST-PLATE 729
relatively feeble intensity. A construction along these lines, the
details of which however are not entirely clear from the meager
account at hand, has been described by Bechstein1 before the
German Illuminating Engineering Society. He states that with
the aperture in the sphere one forty-sixth as large as the surface
of the sphere itself, the cos i error at 70 ° incidence is —6 per.
cent., and the brightness of the field is one third as great as that of
a plaster of Paris plate with the same illumination. Evidently if
the advantages so noted are not over-borne by disadvantages
which are not mentioned, this style of test-plate marks a decided
improvement.
W. D'A Ryan patented a form of test-plate some five years
ago which was intended to obviate the cos i error. This test-
plate consisted of a block of diffusing glass with a dome-shaped
upper surface for the reception of the illumination. Surround-
ing this surface was a low circular screen notched at the top in
such a way that the shadow cast by it on the surface was suffi-
cient to maintain the diffused flux of light in the interior of the
block at its right value with i approaching 900. The dome-shaped
upper surface evidently tended to correct the deficiency of bright-
ness at high angles by presenting a larger surface to illumination
at those angles. This, of course, gave a lopsided distribution of
light on the test-plate, but the thickness of the plate was such
that the flux was undoubtedly fully diffused before it reached the
photometric field. It would seem that there must have been a
very serious loss of light in passing through this thick diffusing
test-plate. The device was incorporated by Mr. Ryan in an
illumination photometer.
Study of Test-plate Errors.— It may be advisable next to study
the errors2 of existing test-plates such as are commonly used in
1 Zeitschriftfur Beleuchtungswesen, March 15, 1915, p. 31.
2 The apparatus used in the study of test-plates was as follows: The telescope was
removed from a spectrometer and to the arm of the spectrometer a light tubular sup-
port was attached, carrying at its outer end an incandescent lamp enclosed except for a
slit in front, by a metal screen. The radius of the circle in which the lamp moved was
about one meter. Transmitting test-plates to be studied were fixed to a portable photo-
meter and adjusted at the center of rotation. Reflecting test-plates were entirely de-
tached from the photometer which then was set up at such a distance that the arm carry-
ing the lamp could be moved in front of it. The angles were accurately read on the
divided ^circle of the spectrometer. With high angles of incidence it is necessary that the
angle shall be measured quite accurately inasmuch as the values of the cosine are chan*-
mg rapidly. 5
730 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
order to inform ourselves as to how serious they are. In Table I
are given variations from the theoretical values shown by two
transmitting test-plates of white glass with the surfaces de-
polished. It will be seen that while the error is of relatively
small magnitude up to about 400, yet beyond that point it becomes
quite serious.
TABLE I.— Errors of Transmitting Test-Plate with
Depolished Surface.
Plate numbers 5 220
Thickness (inches) 0.0718 (1.82 mm.) 0.055 (1.4 mm.)
Angle of Errors, per cent.
incidence , ' »
O0 OO
IO° +0.5 , + 0.5
20° O O
30° — 1-5 — 2-5
40° — 5 — 4-5
500 - 8 - 7
6o° — 8 —10
700 —13 —13
8o° — 24 — 29
85° -33 -37
In the use of reflecting test-plates a complication enters which
is not present with transmitting test-plates, and which arises
from the fact that the reflecting test-plates are usually detached
from the photometer, and the angle at which the photometer
views the plate is not fixed ; nor is the position of the photometer
with respect to the direction of the principal flux of light reach-
ing the test-plates ; i. e., the angle of azimuth. Hence a double
dissymmetry. A transmitting test-plate attached to the pho-
tometer is viewed normally ; hence the brightness of the plate
must be independent of the azimuth of the incident light. The
same thing is true of the reflecting test-plate, provided the grains
of its upper diffusing surface are indifferently arranged and
provided the plate is viewed normally. Ordinarily such test-
plates are viewed with the photometer held in the hand, and the
angle of view may differ from the normal by a considerable
amount, while the azimuth is determined by the convenience of
the operator. The arrangement therefore is not symmetrical
with respect to the photometer.
SHARP AND LITTLE: COMPENSATED TEST-PLATE 731
The data on reflecting test-plates here presented do not repre-
sent a complete investigation but are sufficient for the purpose of
showing some of the peculiarities encountered. Table II shows
TABLE II.— Errors of Reflecting Test-plate of Depolished
White Glass.
In plane of incidence
Vngle of view
. . 0°
30°
45°
Angle of
Incidence
Same
side
Opposite
side
Same
side
Opposite
side
Errors per cent.
o°
0
O
O
0
O
io0
—0.5
+0.5
0
-0.5
O
20°
— I
0
+ 1
0
+ I
30°
— 2
0
0
+0.5
+ 8.5
40°
— 2
0
+ 1
— I
+ 9
50°
— 2
-0-5
+0.5
— c-5
+ 12
6o°
—4-5
— I
+ 2
0
4-20
700
—7-5
+ 0.5
+ 1
—0.5
+29
8o°
—9
—6
+7
— 12
+44
850
— 11
—7
+19
—15
+59
the errors of a depolished white glass reflecting test-plate when
viewed at o°, that is normally, at 300 and at 450 all in the plane
of incidence of the light. It will be noted that at o°, which is the
symmetrical position, the error at 70 ° is — 7.5 per cent. When the
angle of view is changed to 300, a surprising thing is seen;
namely that in the plane of incidence the errors of such a plate
are small all the way to 8o°. And this is true irrespective of
whether the source of light illuminating the plate is on the side
toward the photometer or on the side away from it. When the
angle of view is increased to 45 °, this symmetry vanishes. As in
the former case, from o° incidence to 900 incidence on the side
toward the photometer, the errors are negligibly small. On the
opposite side, however, the errors mount rapidly after 200 is
passed until at 700 the error is -f2§ Per cent- (see Fig. 1).
This indicates a condition of specular reflection, which enters
when the angle of view is as large as 45 ° , which is necessarily
no factor when the light is on the side of the plate toward the
photometer. In order to investigate this effect of the angle of
view more closely, the readings shown in Table III and in Fig. 2
were taken. Here the angle of incidence of the light was main-
tained at 6o° and the angle of view of the photometer was varied,
o
732 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
il
/
-D
/
/
r
>
/
-jp
r<
....
'
1? "^
A.
"^r*5^
-
KA
(
r
i
j
I
j
3
It
4
0
s
a
i
;>
70
80
90
angle: of incidence:
Fig. i.— Reflecting test-plate, viewed in plane of incidence. A. Viewed at 450; lamp on
side toward photometer. B. Viewed at 450; lamp on side away from photometer.
C. Viewed at 300; lamp on side toward photometer. D. Viewed at 300; lamp on
side away from photometer.
20 30
ANGLE OF VIEW
Fig. 2.— Reflecting test-plate viewed in plane of incidence. Angle of incidence = 6o°. The
upper branch of the curve beyond 300 shows the errors when the lamp is on the side
opposite to the photometer. On the same side as the photometer the errors are prac-
tically zero.
SHARP AND LITTLE: COMPENSATED TEST-PLATE 733
It will be seen that the arrangement shows symmetry up to 300
angle of view and that at 25 ° and 300 angle of view, the error
is zero. Above this point the errors increase when the lamp is on
the side opposite to the photometer, whereas when the lamp
is on the same side the errors remain negligibly small.
TABLE III.— Errors of Reflecting Test-Plate of Depolished
White Glass with Constant Angle of Incidence and
Varying Angle of View.
Angle of incidence = 6o°.
Angle of view • • o° 150 250 300 32. 50 350 450
Errors
Same side — 4.5 — 0.5 o — 1 —0.5 o o
Opposite side .. — 4.5 o o +2 +5-° — II +24
TABLE IV.— Errors of Reflecting Test-Plates.
In plane of incidence At right
angles
Angle of view o° 150 300 3oc
Same Opposite
side side
Angle of Errors, per cent,
incidence
0
0
0
0
0
— 2.5
0
— 0.5
— 0.5
+ 0.5
— 3-5
0
+ 0.5
0
0
— 3
0
0
0
0
- 6.5
- 0.5
— 1
— 1
+ 0.5
— 9
— 2
— 1
— 0.5
— 1
— 11
— 2.5
0
0
— 6
—15
— 7
— 7
0
— 7
—23
—13
— 14
3
— S
oa
IO°
2O0
30°
40°
50°
6o°
700
8o°
850 —25 —20 —24 - 3 —18
Data on tests of a commercial test-plate of other manufacture
than the one given above are shown in Table IV. Here again
the errors are smaller with an angle of view of 300 than they are
at o° or 1 50. In a further study of this plate the photometer
was placed so that its angle of view should be 300 to the plate
at right angles to the plane of incidence to the light. The errors
under this condition are given in the last column of Table IV.
In these data as well as in the data of the preceding two columns,
one finds a very good argument for the proposition that a test-
plate of this character should be viewed at an angle of about 300.
A certain amount of dissymmetry is evident but it occurs at such
high angles that it may not be a very important factor.
734 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Causes of Deviations from Cosine Law. — It will be noted from
the foregoing that in all cases where the test-plate is viewed from
a symmetrical position, that is, along the normal, the test-plate
errors are negative at the higher angles. The light incident at
higher angles does not bring the brightness of the plate up to its
theoretical value. More light is needed for this. It is interesting
to inquire into the cause for it.
o°
20
30 40 50 60
ANGLE OF INCIDENCE
70
80"
Fig. 3.— A. Reflection from polished glass, n = 1.5, reduced to zero reflection at normal.
B. Errors of polished white glass test-plate. C. Errors of polished white glass test-
plate. D. Errors of depolished white glass test-plate.
All the light incident on a test-plate is either reflected, absorbed
or transmitted. In the case of a transmitting test-plate the bright-
ness evidently cannot obey the cosine law, even if the glass itself
is a perfect diffuser, unless the loss by reflection is constant for
all angles. The endeavor is made by depolishing the glass to
attain this condition. The reflection of a polished glass surface
at various angles of incidence is shown in Fig. 3, curve A, in
such a way that the values are comparable with test-plate errors
in the tables ; that is, all values are diminished by the percentage
reflected at normal incidence, 4 per cent. If we were to use
as a transmitting test-plate a disk of polished white glass, there
would evidently be an error of 30 per cent, at 8o° due to surface
SHARP AND LITTLE: COMPENSATED TEST-PLATE 735
reflection, quite apart from any failure of the glass to diffuse the
light penetrating it. The actual errors of test-plates made of
polished instead of depolished glass are shown for comparison
in Fig. 3, curves B and C. These curves are evidently what
would be expected if an imperfectly diffusing surface were over-
laid with a smooth glass surface. The lack of diffusion is
evidently less important as a source of error, than the variable
loss by reflection.
In curve D of Fig. 3 are shown graphically the errors of de-
polished plate No. 220. It will be seen that the effect of rough-
ening the surface of the glass is to diminish the loss of light at
the higher angles and hence to improve the plate at these angles.
That a variable loss by reflection still plays a part, however, is
demonstrated by the fact that the light reflected at about the
polarizing angle (560) still shows, when examined through an
analyzer, a considerable percentage of polarization.3 It would
appear therefore that the loss by reflection, following the theoret-
ical law of Fresnel, may be considered as the chief cause for the
deficiency of test-plate brightness at high angles.
PRINCIPLE OF COMPENSATION.
If additional light could be introduced to the plate, so pro-
portioned as to be zero at normal incidence and to increase rapidly
from 500 on, this deficiency might be overcome and the test-plate
caused to give a correct result. It is this idea which underlies
the compensated test-plate, forming the subject of this paper.
The construction is a very simple one. In the transmitting test-
plate the ordinary glass plate instead of being mounted on the
end of a metal tube is mounted on a little diffusing (opal) glass
ring. The brightness of the test-plate with o° incidence is not
altered by the presence of the opal ring except by internal reflec-
tions, but as the incidence increases, a larger and larger amount
of light falls upon the ring, and by it is diffused in such a way as
to add a certain illumination to the under surface of the test-plate.
8 It is clear that in measuring partially polarized light (e. g., skylight) the error of the
test-plate will depend on the relation of the plane of polarization to the plane of inci-
dence. This may be important in the case of reflecting test-plates. Furthermore, pho-
tometers operating on the polarization principle may give erroneous results with a reflect-
ing test-plate of depolished glass or similar material such as celluloid. Such an error
may be eliminated by taking settings with the polarizing apparatus in two positions at
right angles to each other.
736 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
By properly proportioning the transmission of the test-plate and
the transmission and diffusion of the ring, together with the width
of the latter, a compensation for the deficiency in brightness of
the test-plate at high angles may be obtained.
It is evident that if the arrangement as described were used,
light coming at 900 of incidence, which would produce no illumin-
ation whatever on the upper side of the plate, would pass through
the opal glass ring and illuminate the under side of the plate.
Light coming from angles even greater than 90 ° might have the
same effect. Evidently this light must be cut off and this is done
by the interposition of a saucer-shaped screen with the edge of the
saucer in line with the top of the aperture in the opal ring. The
construction used is shown in half -section in Fig. 4, and the
actual test-plate as attached to a photometer is shown in Fig. 5.
Fig. 4.— Compensated transmitting test-plate. P. Test-plate of polished white glass. R.
Ring of opal glass. C. Opaque shield. A. Clear aperture in ring for admission
of light. S. Screen to cut off light at 900 incidence.
It has been found that if the light is admitted to the opal ring
close to the test-plate, the compensating illumination is not uni-
formly distributed over the test-plate, so that at high angles of
incidence the field is irregular. On this account the aperture in
the ring is placed well below the test-plate. The portion of the
opal ring through which light should not pass is covered up by a
metal band, the width of which determines the width of the
aperture in the compensating ring and hence the amount of com-
pensating light.
SHARP AND LITTLE: COMPENSATED TEST-PLATE
737
Evidently the amount of compensating light has to be accur-
ately proportioned to fit the peculiarities of the test-plate. If the
test-plate is quite thin and transparent, a larger amount of com-
pensating light is required than if it is relatively dense. The
more perfect the diffusing qualities of the test-plate, the less
compensating light is required. It has been found in practise that
the opal ring may be optically quite thin ; that is it may be clear
glass with a light flashing of opal. A ring of this character asso-
ciated with a polished test-plate gives a combination which is quite
Fig. 5.— Compensated test-plate in practical form.
readily adjusted by varying the width of the annular aperture in
the ring to conform with the cosine law even at very high angles
of incidence.
Polished Versus Depolished Plates. — There are very consider-
able advantages accruing from the use of polished test-plates
rather than depolished ones. In the first place a polished plate is
more uniform in its characteristics than the depolished one and
hence is more easily compensated for its error. The depolished
plate varies according to the means used in removing the polished
surface whereas the polished plate is not subject to this source of
738 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
irregularity, provided the polish is made sufficiently good.
Furthermore depolished plates are very difficult to clean ; minute
quantities of dirt become embedded in the irregular surface and
cannot be removed, while polished plates offer no difficulties
whatever in this respect.
Results of Compensation. — In Table V are given the results
TABLE V. — Transmitting Test-phase of Polished Glass without
and with Compensating Ring of Flashed Opal.
Plate B
uncom-
pensated
Plate B un-
dercompen-
sated W32 in.
^4.0 mm.)
aperture
Plate B
com-
pensated
3/ie in-
(4.8 mm.)
aperture
Plate A
uncom-
pensated
Plate A
com-
pensated
Plate A
compen-
sated in
permanent
mounting
Angle of
Error, per cent.
Lncidencc
o°
0
O
O
O
O
O
IO°
+ 0.5
— 0.3
+ 0.5
O
O
O
2O0
+ 0.5
O
O
O
O
O
30°
+ 0.5
— 0.5
—0.5
— 1-5
—0.5
+ 0.5
40°
+ 0.5
— 0.5
+0.5
— 4
+0.5
+ 1.5
50°
— 3-5
+ 0.5
—0.5
- 6.5
—0.5
+ I.O
6o°
— 11
O
O
— 13-5
—0.5
+ 1.5
700
—20.5
— 2.5
+ 1
— 15
— I
O
8o°
-44
—13
+ 1
-48
—1-5
— O.5
85°
—72
— II
+6
—
—4
— II
obtained in compensating two different plates. In the first column
are shown the errors of an uncompensated polished plate ; in the
second column are shown the errors when this plate is under-
compensated, the aperture in the opal ring being too narrow. In
the next column are shown the results of a perfect compensation
with the opening in the aperture of the ring only 1/32 in. (0.8
mm.) wider than in the preceding case. In the next column an-
other uncompensated plate is shown followed by results of the
same plate compensated. In the last column are shown the errors
of a compensated test-plate in practical form for using on the
photometer. Remembering that measurements made at 85 ° of
incidence are subject to large errors due to the great effect of
small inaccuracies in the measurement of the angle and to the
relative darkness of the field, it may be said that in all cases the
outstanding errors are within the errors of observation.
Compensated Reflecting Test-Plate. — The construction where-
by reflecting test-plates may be compensated in accordance with
the above-mentioned principles is quite as simple as that of the
SHARP AND LITTLE: COMPENSATED TEST-PLATE
739
transmitting test-plate. The reflecting test-plate proper is made
of a disk of depolished white glass; parallel with this disk is
placed another similar disk. A similar opaque screen is used for
shielding the upper disk from light coming at angles of 900 and
TABLE VI.— Compensated Reflecting Test-Plate.
Viewed Normally.
Angle of incidence Error, per cent
o° o
lo° _ 0.5
2°° - 1-5
30° - 1.5
40° — 2.0
5°° — 0.5
60° _ 0.5
7°° + 4
8o° + 2
85° -12
greater. Compensation is affected by the light reflected from the
lower disk which passes through the upper disk and adds a suf-
ficient amount to the brightness of the test surface. This con-
struction is shown in section in Fig. 6. Table VI shows the re-
.•11 • in 1 1 111,, — 1 r0 — r
1 bmbjmJimm .*-">'
Fig. 6.— Half section of compensated reflecting test-plate. P. Test-plate of depolished
white glass. C Compensating diffuser of depolished white glass. S. Screen for cut-
ting off light at go°.
suits obtained with this form of construction. The angle of view
of the photometer was normal to the plate. Here again the re-
sults of the compensation, while not quite so good as in the case
of the reflecting plate, are, for practical purposes, about as
good as could be desired. It should be noted, however, that the
reflecting plate suffers under the disadvantage that in order to
give these results, the angle of view must be normal to the plate.
There does not seem to be any way of obviating this disadvantage.
Also, the reflecting plate is considerably more cumbersome than
the transmitting plate on account of its dimensions. Evidently,
740 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
the plate itself must be of sufficient size to cover the entire
field of the photometer when the photometer is placed at the de-
sired distance from it. The shading ring surrounding it must be
large enough so that it does not begin to cast a shadow on the
lower plate at too small an angle of incidence, for otherwise the
compensation at high angles of incidence will be incomplete. In
the construction investigated the test-plate had a diameter of
5 in. (12.7 cm.) and the entire apparatus a diameter of 10 in.
(25.4 cm.).
The results of a number of the above tests are for convenience
summarized in the curves of Fig. 7.
RESULTS OF ILLUMINATION TEST.
In order to form an idea of the magnitude of the errors which
may be introduced into the results of illumination measurements
►IU
. 4
► .
U
'
^
-
_ —
^
L- --
---i
—A
VI
D
•10
s
E
\
\ i
20
V
\
30
\
A
\
\
\
B
\
- — -
1
y
1
u
i
0
3
0
1
4
0
or T
0
NCI
b
JEN
0
ce:
7
0
B
0
H
0
11
0
Fig. 7. — Errors of various test-plates viewed normally. A. Depolished transmitting plate.
B. Polished transmitting plate. C Depolished glass reflecting plate. D. Compen-
sated transmitting plate. E. Compensated transmitting plate.
through test-plate deficiencies, an actual test of the illumination
in a room at the Electrical Testing Laboratories was made. The
results with a compensating test-plate were taken as standard and
the others compared with them. The system of illumination was
semi-indirect and may be taken as fairly typical of good modern
practise.
The results as given in Table VII show a deficiency of 5.5 per
cent, in the values yielded by the uncompensated transmitting
test-plate and of 13.5 per cent, in the values of the reflecting test-
SHARP AND LITTLE: COMPENSATED TEST-PLATE
741
plate, which was viewed normally. The value 13.5 for the error
of the reflecting test-plate is much larger than would be expected
from the test results of such plates given above. The discrepancy
may properly be ascribed to the light cut off from the plate by
the photometer and the operator. However, this source of error
is rarely, if ever, absent in using reflecting test-plates in interiors
where the light is well diffused, and constitutes a serious disad-
vantage of the reflecting test-plate as compared with the trans-
mitting type.
TABLE VII.— Comparison of Test-Plates in Measuring Illumina
tion in a Room.
Uncompensated transmitting
Uncompensated reflecting
test-plate viewed normally*
Test
transmitting
Per cent, of
Per cent, of
station
Foot-candles
Foot-candles
compensated
Foot-candles
compensated
I
12. 1
11. 7
97
10.9
90
Check after test
12.2
11. 7
96
II. O
91
2
9-1
9-°5
99
8.15
89
3
5-05
4.69
93
4-03
80
4
2.6l
2-53
97
2.25
86
5
6-35
5-85
92
5-5
87
6
4.50
4.04
90
3-69
82
7
2.64
2-57
97
2.18
83
8
9-35
9-i
98
8.6
92
9
4.68
4.90
95
4.24
86
10
2.68
2.48
93
2.38
89
11
12.9
12.5
97
12. 1
94
12
8-95
8.55
95
8.05
90
13
4.90
4-45
9i
4.27
88
14
2.71
2.58
95
2.26
83
15
5-95
5.65
95
5-4
9i
16
4-33
4.02
93
3-58
83
17
2-59
2-34
90
2. 11
82
18
9.8
9-15
94
8.25
84
19
4.83
4.70
97
4.16
86
20
2.76
2-55
93
2.15
78
21
12.9
12.8
99
11. 8
92
Mean
illumination •
• 5.21
4-95
4-5i
Percentage
of
compensated .
94-4
85.5
* Errors due in part to shadow of observer and of photometer.
If the 5 per cent, error as shown by the uncompensated trans-
mitting plate be taken as typical, it will be seen that in all prob-
742 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
ability test-plate errors have not been a very serious matter from
a practical standpoint, but it must likev/ise be conceded that to
eliminate them entirely is very 'desirable.
Application to the Integrating Sphere. — In the theory of the
integrating sphere the assumption is made that the window, the
brightness of which is observed, is a perfect diffuser. Experi-
mental work is now in progress looking to the adaptation of the
compensation idea to these plates with a view to attaining a higher
accuracy in sphere work.
APPENDIX.
Brightness of Test-plates as Seen in the Photometer when
Measuring an Illumination of One Lumen Per
Square Foot.
Apparent lumens
Cp. per sq. in. emitted per sq. ft.
Depolished, transmitting 0.00049 0.22
Polished, transmitting 0.00056 0.25
Thick white flashed opal 0.00048 0.22
Thin greenish, flashed opal 0.00123 0.56
Depolished glass, reflecting 0.0180 0.81
The above-given figures represent the results of test of one
plate only of each kind and are to be taken only as approximately
indicative of the performance of the various classes. In the
measurement of feeble illumination particularly, the plates having
a relatively large brightness permit photometric settings to be
made more easily.
DISCUSSION.
Ward Harrison : One redeeming feature of the test-plate er-
ror is that if the photometer measures 3 foot-candles it can be
confidently asserted that more than that is being obtained rather
than less. Its worst characteristic is that it usually tends to
magnify variations in intensity of illumination. For example, in
a photometric survey, the measurements taken near the side walls
of a room will indicate a much lower intensity than in the cen-
tral portion. The illumination is generally somewhat lower any-
way, but since most of the light falls obliquely on the test plane at
these stations, the test-plate error becomes a considerable factor
and the photometer reading is still further reduced. The illumina-
tion on a desk in this portion of an office is often much more
satisfactory than would be indicated by a foot-candle reading.
COMPENSATED TEST-PLATE 743
Again, in the case of industrial plants the fact has just been
emphasized that illumination measurements should be made with
at least one lamp shaded. A man working at his machine will
often shade his work from the lamp placed directly above him, or
nearly so, and if the residue of the illumination is measured, one
may be unnecessarily startled at the low values obtained. It is
simply another case of oblique lighting and the actual intensity
may be easily 20 per cent, greater than the quantity measured.
Perhaps the most glaring of all cases of this error is that en-
countered when one attempts to measure horizontal illumination
in a street lighting installation. Five and one-half per cent, has
been given as the average error due to the use of an ordinary test-
plate as determined in an illumination survey of a room equipped
with a semi-indirect system. We have made several investiga-
tions where the error of the old type of plate appeared to be con-
siderably greater than this. The magnitude of the error depends
of course upon the character of distribution from the light
sources ; units which emit most of their light at angles near the
vertical will give rise to a much less error in an illumination test
than will units having a wide distribution of light. In the case of
a semi-indirect installation the portion of the light which is re-
flected from the ceiling has a circular or concentrated distribu-
tion and the same is also often true of the portion of the light
which is supplied by the bowl itself. With a system of direct
lighting units having an extensive distribution, it has been found
that the error in mean intensity runs as high as 10 or 12 per cent.
In conclusion I wish to express my appreciation of the work of
Dr. Sharp and Mr. Little in producing this new test-plate. It will
certainly afford a great degree of mental satisfaction to all who
have occasion to make illumination surveys ; from a practical
standpoint the satisfaction is much increased by the fact that the
test-plate has a polished surface. It is therefore not so liable to
the very common error due to dust which is especially serious
where an instrument is calibrated in one place and at a later date
operated in another.
G. H. Stickney: This paper apparently confirms the distrust
which I have held for many tests made with the reflecting type of
test-plate. I have never used such test-plates to any extent, but
744 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
I have noted the very optimistic use of them by others. How-
ever, it must be recognized that such test-plates are exceedingly
valuable for certain classes of measurements and when properly
used give very useful results.
At the Boston Convention in 1907 (see Transactions 1907,
pages 559, 562 and 571) some mention was made of an illumina-
tion photometer developed under the direction of Mr. W. D'A.
Ryan, with which I had something to do. As Dr. Sharp says, this
photometer was not particularly suitable for very low intensity
measurements. It, however, met quite well the requirements
in the class of problems which we were then meeting. It was
never claimed for this photometer that it was suitable for all sorts
of illumination measurements. It had the advantage over all
other existing photometers in giving the proper value of light fall-
ing at all angles. In view of the fact that the discrepancy was
then realized, it is somewhat surprising that up to the present no
device has been in common use to effect a similar correction.
The arrangement described in the present paper seems to me to
be an exceedingly important one, which should be applied as far
as possible in all measurements taken in interiors where there is a
large component of side light, either from reflecting walls or
otherwise. The new device seems to embody some of the same
fundamental principles of Mr. Ryan's photometer, although the
method of mixing the light is of course quite different.
I believe we frequently encounter serious error in illumination
measurements in undervaluating the diagonal light which often is
most valuable in securing good illumination. For example, in this
room at the present time, with the daylight coming in at the side
windows, an ordinary photometer plate would not properly meas-
ure the light on the chairman's table, although it would more cor-
rectly measure the artificial illumination. I do not think this
would be a happy instance to illustrate the excellence of the meas-
uring qualities of an ordinary plate as commonly used in illumina-
tion photometers.
Mr. P. S. Milear: There have been two conditions surround-
ing the use of erroneous test-plates which have tended to reduce
the ill effects of such errors. First, most surfaces which have
been viewed in practise depart from the cosine law in the same di-
COMPENSATED TEST-PLATE 745
rection as do inaccurate test-plates. Second, the error has been
more or less a systematic one applying in a general way to all
photometric results and therefore less misleading than it might
have been if applied to comparative results.
In spite of these conditions users of portable photometers have
been uneasy regarding the test-plate error which has affected
much of their work. It is accordingly very gratifying to know
that we are in a fair way to eliminate such errors and I want to
express my appreciation of the work of Dr. Sharp and Mr. Little
in making available a practical device with which this last remain-
ing systematic error can be removed from illuminating photo-
meters.
Dr. C. H. Sharp (In reply) : One speaker quite properly call-
ed attention to the fact that the reflecting test-plate, when prop-
erly used, apparently is inherently less in error than the trans-
mitting plate. I believe, however, that because it can be viewed at
pretty much any angle and is liable to be so placed that the body
of the observer or instrument will cut off some of the light which
it ought to get, it has disadvantages as compared with the test-plate
rigidly attached to the photometer, which in practise renders it
less reliable. I think Mr. Stickney has answered very well the
question of the value of the light at 80 degrees. Very often it is
not very important, and then again it may be very important, and
when it is important, we surely want to be able to measure it. As
to the area of the field in the apparatus illustrated, the diameter
of the field is only about half the diameter of the transmitting
test-plate. In a reflecting test-plate, the area of the field depends
upon the distance of the photometer away. There has, however,
been no practical difficulty due to an irregular field caused by an
irregular distribution of the compensating light; the field is
regular to a satisfactory degree. I perhaps should have said
more in presenting the paper regarding Mr. Ryan's instrument.
Ryan's compensated test-plate, for that is what it was, was a very
ingenious thing. It was an endeavor to meet a difficulty which,
even at that relatively early day, was well recognized, and it is
probably a misfortune that it was not followed up.
746 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
PRESENT PRACTISE IN THE LIGHTING OF
ARMORIES AND GYMNASIUMS WITH
TUNGSTEN FILAMENT LAMPS.*
BY A. E. POWELE AND A. B. ODAY.
Synopsis: The general requirements for lighting are here discussed
from a practical viewpoint. Typical installations are pictured and briefly
described; and data covering a considerable number of buildings are pre-
sented in tabular form, giving dimensions, spacing, hanging height and
size of lamps, type of reflector, equipment, etc. From this data average
values of power consumption per unit of area (watts per square foot) are
obtained.
INTRODUCTION.
A careful search through the Transactions of the society and
of technical literature reveals but little data on this field of light-
ing. It is true that the lighting of these buildings is a relatively-
simple proposition, yet the engineer who is about to design a new
system usually desires to have available data with which to check
his calculations. The authors of the paper were in a position to
examine a considerable number of typical installations and cor-
relate the material. They make no pretense of originality of
design as the lighting of but comparatively few of the buildings
inspected was planned by them.
The method of procedure in preparing the paper was to visit
representative armories and gymnasiums located within a con-
venient radius of New York City, and note the facts as enumer-
ated in the text; and, next, from observation and experience, to
outline the principles involved in the lighting, as far as possible
include these with the data.
Illumination tests were conducted in only a few instances as
the time and expense, which would have been involved, would
not have been warranted, for the illuminating efficiency of
standard equipments is now fairly well known or can be estimated
quite closely from similar cases. For checking calculations, the
watts per square foot of floor area, with the proper modifications
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
POWELL AND ODAY: ARMORY AND GYMNASIUM LIGHTING 747
deduced from experience, proves very useful. In each case the
actual watts per square foot are given, but since the efficiency of
the lamps found in service varies from 0.6 to 1.05 watts per hori-
zontal candlepower, a table headed "Comparative watts per square
foot" based on i watt per candle or approximately 10 lumens per
watt is also included.
ARMORIES.
When one thinks of an armory, the drill shed alone is usually
pictured; yet some of these structures are very elaborate indeed,
having also a gymnasium, theatre, rifle ranges, bowling alleys,
billiard room and the like. The subject therefore may be sub-
divided as given below.
Drill Shed. — This is, of course, the most important part of the
armory and should receive the most attention. As a general
proposition the usual form is a large open space with an arched
roof. The size of those investigated varied from 600 ft. x 300 ft.
(182.88 x 91.44 m.) (180,000 sq. ft.) x 100 ft. (30.48 m.) high,
to 76 x 92 (23.16 x 28.04 m0 (7,ooo sq. ft.) (n.58 m.) 38 ft.
high. The roof is often partly glass to admit daylight and
usually the iron work is exposed.
Many drill sheds have balconies for the seating of spectators,
necessitating special lighting below to prevent dense shadows
which would result if only the general lighting was provided.
The floor varies considerably depending on the branch of service,
cavalry having a very dark brown tanbark; infantry, light hard
wood. Naturally the character of the floor has a marked effect
on the quantity of light which must be supplied.
On account of the simplicity of operation and maintenance, the
high efficiency of light production, the pleasing color of light, the
steadiness and adaptability to reflectors giving any desired distri-
bution of light, the gas-filled, tungsten filament lamp has
become practically the standard illuminant for lighting drill sheds
in the territory investigated. The large areas permit the use of
high candlepower units and the lofty ceilings give hanging heights
such that lamps are always well out of the ordinary angle of
vision, overcoming any objection which might be raised on the
question of intrinsic brightness. The wide range of sizes avail-
able make it possible to select a unit fitting any chosen spacing
748 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
giving the desired watts per square foot or foot-candles. In-
expensive fixtures, holders, sockets and reflecting devices are
all standardized, thus avoiding the added cost of special designs
which are sometimes attendant on propositions of these mag-
nitudes.
The uses to which the drill hall is put are somewhat varied.
The drilling of raw recruits takes place on only a portion of the
floor and does not require the entire area to be lighted ; battalion
and regimental drills and reviews necessitate full illumination
for ease of manoeuvres and inspection; gun drills in the coast
defense and artillery sometimes need all lights out ; or the armory
is often rented to charitable organizations and the like for fairs
and bazaars, which demand brilliant lighting as well as special
decorative or spectacular effects. In any event sufficient light
must be provided in all parts of the room to meet the most ex-
acting conditions.
Type of Unit. — Appearance is one of the factors which must
be given consideration, as the general effect of the room must be
attractive, particularly if used for other than regimental purposes.
Efficiency must also be considered as there are large areas to
be illuminated and an extravagant fixture would make the cost of
proper lighting prohibitive.
Eye protection must be assured as glare in such work as gun
training would materially reduce the effectiveness of the unit.
Since the ceilings are usually broken by trusses and often quite
dark, as a general proposition direct lighting is essential.
In most cases it is advisable to use either a translucent re-
flector or a unit which permits some of the light to escape above
the horizontal, for if the ceiling is totally dark ones attention is
involuntarily attracted and the room seems unpleasant. Occas-
ionally, however, the floor is light enough to reflect sufficient
light back to the ceiling even if opaque bowl reflectors are
employed.
The type of distribution will vary with conditions. If the side
walls are quite dark a unit giving a wide curve is inadvisable as
far too much flux will be wasted by wall absorption. With light
walls, however, the diffuse reflection will assist in the general
illumination and concentration of the light is not as necessary.
Fig. I. — Night photograph 7th Regiment Armory X. G. X. Y., lighted by 1,000-watt gas-
filled tungsten lamps in two-piece prismatic enclosing globes ; average illumination
3.3 feet candles.
F'g- 2.— Xight photograph 71st Regiment Armory X. G. X. Y., lighted by soo-watt gas-
filled tungsten lamps in bowl prismatic reflectors.
Fig. 3.— Night photograph Troop C Armory N. G. N. Y., lighted by 750-watt gas-filled tung-
sten lamps in deep bowl dense opal reflectors, average illumination 3.24 foot-candles.
Fig. 4.— Night photograph 22nd Regiment Armory N. G. N. Y., lighted by 1000-watt
gas-filled tungsten lamps with deep bowl enameled steel reflectors.
POWELL AND ODAY I ARMORY AND GYMNASIUM LIGHTING 749
Ease of Cleaning and Renewals. — On account of the high
hangings employed, some sort of a lowering device should be
provided. Most of the single unit fixtures weigh so little that a
simple steel cable will safely support them ; a cut-out hanger with
lowering rope or wire simplifies this phase of building main-
tenance. In some cases the cut-out is omitted and the cable
passes through a pulley, then down the sides of the room, the
current-carrying wires hanging in loops.
Convenience of Control. — Although often not considered, this
is an important point ; for instance, in the coast defense armories
when practising with the guns it is often desirable to hurriedly
turn off any group of lamps. In the Brooklyn armories remote
control is employed. The man in charge of the entire floor has
a board with pilot lights and switches. At each gun are a num-
ber of push buttons, so that when the squads are firing the officer
in charge of the firing can at once signal for any group of lamps
to be extinguished. The whole armory can be thrown in dark-
ness in an extremely short time. With the system of lighting
formerly employed it required twelve men for this work with
the attendant delay.
Intensity of Illumination Desirable. — From general consider-
ation the cavalry and field artillery armories would require less
light than those of the other branches of service, as they are
not likely to be used for social purposes. This is counteracted,
however, by the fact that the tanbark or loam floor absorbs a
great deal of light and makes the place appear abnormally dark.
Average Figures. — The actual average watts per square foot
for 15 drill halls with wood floors was 0.39; comparative 0.58 ;x
for the 6 armories with loam and tanbark, actual 0.34 ; compara-
tive 0.52.
Rifle Range. — The satisfactory illumination of this part of the
building is too large a subject to be treated with any degree of
completeness in a paper of this nature. In fact the British Il-
luminating Engineering Society devoted their entire May meeting
to this phase of the art. A very valuable paper, by Mr. A. P.
Trotter, and interesting discussion is reported in their June
Transactions.2
1 i. e. with lamps at 10 lumens per watt.
2 See Illuminating Engineer, (L,ondon) June, 1915.
750 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
So many facts enter into the problem, such as glare, contrast,
intensity, uniformity, surface brightness, type of sight employed
and so on, that it seems advisable to avoid all attempts at out-
lining the proper practise. Those interested can study the above
reference.
However as an indication of the American practise a descrip-
tion is given of two indoor ranges, the first rather elaborate and
the second simple.
There are two rifle ranges at the 69th Regiment N. G. N. Y.
Armory, each 120 yards (109.72 m.) in length: in brief, they
consist of two tunnels approximately 10 ft. (3.04 m.) high and
14 ft. (4.26 m.) wide, walls of brick and the ceiling of concrete.
General illumination is provided in the firing room by small lamps
and diffusing glassware. Across the tunnel at both the 50 and
75-yard (45.72 and 68.58 m.) points are placed mirrored trough
reflectors12 pointing downward, with 16 25-watt clear lamps
each. A short distance above and in front of the targets (which
are 2 ft. x 3 ft. 0.60 x 0.91 m. in size) is placed a third mirrored
trough12 reflector giving an asymmetrical distribution. In this
25-watt lamps are placed on 8 in. (20.32 cm.) centers. Heavy
crystal glass plates are set in the floor in front of each target and
the direct light from the reflectors passes through these and serves
to illuminate the telephones and enables the scorers in the butts
to prepare fresh targets. The night view in Fig. 6 was taken
at the 60-yard mark or approximately midway between the two
sets of lights in the gallery.
Princeton University has a short range with four targets which
are controlled from the shooting position by means of a con-
tinuous wire and hand wheel. Above each target position is
located a 60-watt clear lamp in a 45 ° angle aluminum finish steel
reflector13 12 in. (30.48 cm.) in front of and 18 in. (45.72 cm.)
above. The average illumination on the targets is approximately
12 foot-candles and is quite even.
Offices, Board and Company Rooms. — These are in fact club
rooms with uses similar to those of the residential living room.
Decorative yet comfortable lighting should be provided; the in-
tensity must be fairly high and illumination even, owing to the
diversified requirements ; for cards, reading or writing in any
POWELL AND ODAY: ARMORY AND GYMNASIUM LIGHTING 75 1
part of the room, piano playing and singing. There seems to be a
tendency to decorate the rooms with dark finishes which, of
course, detract from the apparent brightness of the room. The fur-
nishings of some of these rooms are very elaborate ; for instance,
over $8,000 was expended on the quarters shown in Fig. 9.
Yet in many such cases but little attention has been paid to the
lighting system and its decorative qualities have been neglected.
The fixtures used are often quite commercial, whereas an ex-
cellent field is offered for special designs in etched and colored
glassware and appropriate metal work. One can conceive how
the artist could work into the glass decoration, the company
letter, U. S. A. monogram, or the eagle in a similar manner to
those emblem bowls designed for lodge rooms with the elk's head,
square and compases, etc. Diffused semi-indirect lighting with
appropriate fixtures seems to be one logical method of treating
this part of the building.
A view of the quarters of Company K, 71st Regiment N. G.
N. Y., 20 x 45 ft., lighted by 36 25-watt tungsten filament lamps
in prismatic enclosing globes '* and *s on "shower" fixtures and
three arm brackets, is shown in Fig. 8. This rather high wattage
is necessitated by the finish of walls and ceiling.
Company Locker Rooms.— Utility of equipment is essential
here with lamps located between rows of lockers and fitted with
efficient reflectors. Somewhat higher illumination should be pro-
vided in the neighborhood of the mirrors to facilitate dressing.
Company Store Rooms.— The accoutrements and spare supplies
are placed on racks or shelves and must be fairly well illuminated
for inspection and ease of locating a given article. Efficient
equipment, so placed that an even intensity will be produced over
the shelves, should be used. The work bench, which is often lo-
cated in this room, should have one or two well shaded localized
lamps; for minor repairs and cleaning of arms and other ap-
paratus are carried on here.
Offices.— The lighting requirements of the private office have
already been discussed before the society, and the practise is
fairly well established. The regimental officers' rooms present no
especial problem.
Corridors.— A low intensity of light is sufficient here; in the
752 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
less frequented parts of the building there should be sufficient
light to prevent stumbling; but the main corridors should have
enough illumination to readily distinguish a passerby, and to avoid
any danger of accident in the event of a crowded condition.
The band room, quartermasters' and armorers' departments
offer no especial problems beyond that of the average interior.
Stables. — The stables for the cavalry horses are often located
in the basement of the armories ; comparatively little light is re-
quired and the lamps should be of low candlepower, so that they
can be placed at fairly frequent intervals without excessive energy
being consumed. The ceilings are usually low and if too wide
spacing is used some of the stalls will be in deep shadow. A
fairly satisfactory arrangement is that of Squadron A, New
York City. There is an aisle approximately 15 ft. (4.57 m.) wide
between rows and stalls. Two rows of 25-watt clear lamps are
used in each aisle without reflectors close to the whitewashed
ceiling, one in front of every second stall. This gives plenty of
light for harnessing, cleaning and feeding the horses, and the
passageway is well illuminated.
GYMNASIUMS.
As in the case of the armory, the subject must be divided into
several sections the first of which is the
Main Exercising Floor. — This is usually rectangular in shape
with a moderate height of ceiling. The arrangement most fre-
quently used has the running track as a balcony 6 to 8 ft. wide
around all four sides of the room. In the center of the main
floor are the principal pieces of apparatus, horses, bucks, jump-
ing standards and parallel bars, while the flying rings and hor-
izontal bars hang from the main ceiling. These can usually be
pushed aside or drawn up out of the way for basketball, indoor
baseball and wrestling, matches or practise. Below the balcony
are found the exercisers of the various types and racks for wands,
dumb-bells and Indian clubs.
The center part of the space requires even illumination of a
moderate intensity with lamps so located that the hanging appar-
atus will not cause dense shadows. Particular attention should
be paid to the shielding of the eye from the lamp filament, for one
is forced to look upward a great deal when playing basketball.
75-2-
* I F r Hi r ,
J ^J ^ : ■ IBB
lair rrKOL
Fig. 5.— Night photograph U. S. Naval Academy, Annapolis,[lighted by 1000-watt gas-
filled tungsten lamps with enameled steel reflectors^andjdiffusing globes.
Fig. 6.— Night photograph rifle range
69th Regiment N. G. N. Y.
Fig. 7. — Night photograph rifle range
Princeton University.
Fig. 8.— Night photograph, Club Room Company K, 71st Regiment N. G. N. Y.
Fig. 9. — Night photograph main exercising room Princeton University gymnasium
lighted by 250-watt bowl-frosted tungsten lamps in dome
shaped enameled steel reflectors.
powell and oday: armory and gymnasium lighting 753
If possible a slightly higher intensity should be provided in the
neighborhood of the basket to facilitate shooting.
The illumination on the apparatus attached to the side wall
below the track need not be as high as in the open space, yet in
many cases it is necessary to provide a few outlets here with
small lamps properly shaded to prevent dense shadows.
The general discussion on choice of a unit given under armories
applies here also.
It is a regretable fact that in over 50 per cent, of the gymnas-
iums examined an old type of equipment was employed. This
consisted of a 3, 4, 6 or 12-lamp cluster body with a white glass
or enameled steel flat reflector about 12 or 15 in. (30.48 or 38.1
cm.) in diameter; in most every instance these were placed close
against the ceiling and surrounded by wire cages or guards. This
device is unsightly, gives a poor distribution of light, is inefficient,
as light from one lamp must pass through the adjacent bulbs, and
finally the whole of the filament is exposed to the eye. It would
require too much space to tabulate the detailed data on all of these
installations so the average figures are alone presented.
TABLE I. — Average Data on Gymnasiums Lighted by Tungsten
Filament Lamps in Clusters.
High Schools
Colleges
Y
. M. C A.
Number examined, 19
Number examined, 6
Number examined, 5
Min.
Max.
Avg.
Min.
Max.
Avg.
Min.
Max.
Avg.
Area in sq. ft •
640
8,200
3.56o
800
7,600
3,340
1,650
5,600
3,IOO
Ceiling height
9
31
17
12
30
19
15
25
23
No. outlets • • •
3
43
15
3
5
4
4
18
9
No. lamps ....
12
252
73
20
32
30
16
108
54
Total watts. ..
300
5,800
1,635
500
3,000
1,200
960
2,700
1,880
Watts per sq. ft,
Actual
O.26
1. 1
0.65
O. IO*
I. OO
0.63
0.48
0.85
0.62
Comparative
O.25
1.05
0.63
O.O95
0.95
0.60
0.46
O.90
o.59
* It seems unfortunate that the minimum watts per sq. ft. was found in a university
of first rank.
As examples of more modern practise the following table is
given, classified as to the type of reflecting device employed. (See
Appendix No. 2.)
Space is not available for photographs showing all the dif-
ferent types of equipment in use. Fig. 9 illustrates the use of
the dome shaped steel reflector16 in the Princeton University
gymnasium. An illumination test conducted on this floor showed
the following results. The lamps are spaced closer to the center
than ordinarily, as it was desirable to have the basketball court of
754 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
a higher intensity than the sides of the room. The minimum read-
ing on a 30-in. (76.2 cm.) horizontal plane in the court was 2.7
foot-candles, the maximum 3.25 with an average of 2.95. Read-
ings close to the wall apparatus indicated an illumination of about
1 foot-candle on the horizontal plane.
Fig. 10 shows the Union College gymnasium as it appears by
night; a rather large white enameled reflector with concentric
corrugations to break up striations is used above the lamps and
a medium density opal deep bowl hangs below, shielding the eye
and diffusing the light. Detailed data is given in Appendix No. 2.
Two other installations of those described should have slight
additional explanation. In the Columbia University's main gym-
nasium the ceiling above the basketball court is largely openwork
for ventilation. There are fifteen sections, each of which is
further divided into nine squares. The metal work of the center
square in each section was removed and 250-watt lamps in deep
mirrored glass reflectors19 are set with the mouth flush with the
ceiling. This directs a strong light downward and the lamps are
not visible unless one looks directly upward.
Below the running track or balcony, the under side of which is
23 ft. (7.01 m.) from the floor, are placed 14 150-watt lamps in
deep bowl medium density opal glass reflectors.28 These provide
good illumination on the side wall apparatus and at the same
time give some light in the horizontal direction, overcoming the
"dead" effect which would result if only the strongly directional
light was employed.
In the Northwestern University gymnasium deep bowl mir-
rored reflectors1" are also used for direct lighting, but to prevent
the ceiling being dark these units are placed on sheet iron cases
and two small mirrored reflectors29 with 25-watt lamps are used
at each outlet for indirect illumination. The sides of the casing
are cut away and art glass inserts reveal the monograms of the
university in color.
For the twenty-two buildings, the data regarding which are
given in Appendix No. 2, the average watts per sq. ft. is actual
0.78, comparative 0.90.
Swimming Pool. — These rooms are usually rectangular in
shape with white tile walls and ceiling, in fact from a lighting
Fig. 10.— Xight photograph main floor Union College gymnasium lighted by 400-watt
tungsten lamps with enameled steel reflectors and diffusing bowls.
Fig. 1 1. —Night photograph swimming pool Princeton University, lighted by 250-watt
bowl-frosted tungsten lamps and dome shapped enameled steel reflectors.
Fig. 12. — Xight photograph swimming pool Union College, lighted by 150-watt bowl-
frosted, tungsten lamps and bowl shaped light density opalescent glass re-
flectors.
Fig. 13.— Night photograph gymnasium locker room, lighted by 60-watt tungsten
lamps and flared prismatic glass reflectors.
POWELL AND ODAY: ARMORY AND GYMNASIUM LIGHTING 755
standpoint they are practically modified Ulbrich spheres. The
type of reflecting device employed makes but very little difference
in the illumination.
The following data were obtained from examination of eight
pools with various reflecting devices; viz., prismatic glass bowl,
opalescent glass bowl, mirrored glass bowl, cluster body, flat
white glass shade and enameled steel flat dome.
TABLE II.— Illumination Data Indoor Swimming Pool.
Min. Max. Avg.
Area in sq. ft. 760 4,600 2,400
Ceiling height 9 24 13.5
Total watts 400 3,150 1,140
Watts per sq. ft.:
Actual 0.31 0.70 0.47
Comparative 0.30 0.78 0.50
The swimming pool at Princeton University is approximately
35 x 130 ft. (9.14 x 39.62 m.) and is lighted by seven 250-watt
bowl- frosted lamps in enameled steel dome-shaped reflectors16
located in a row down the center of the room between girders. By
means of a temporary bridge illumination readings were taken
on the surface of the water, giving an average of 1.7 foot-candles.
It is to be noted how clearly visible is the floor of the pool al-
though containing from 4 to 10 ft. of water. (See Fig. 11.)
The pool at Union College, Schenectady, as it appears by night
is pictured in Fig. 12; 150 watt bowl-frosted lamps are used in
light density opalescent glass reflectors, bowl shaped 10 in. in
diameter,30 placed in three rows, on equal spacings. The dimen-
sions are 45 x 100 ft. (13.71 x 30.48 m.) giving 0.70 watt per
sq. ft. Here also the lanes marked on the bottom of the pool are
clearly visible.
Shower Room. — These present no especial problem in regard
to the lighting, but on account of the high percentage of vapor
present in the air it is advisable that moisture-proof electric fit-
tings be employed.
Locker Rooms. — Double rows of lockers, with aisles between
in most cases, extend to the ceiling. The athletes dress in these
aisles. Mirrors are ordinarily placed at the ends of rows on the
main aisle. Low ceilings of light color make practical the use of
low candlepower, all-frosted lamps without reflectors, with sock-
756 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
ets set flush. In a number of the installations examined 25-watt
lamps are used on 8 ft. centers. Larger lamps with suitable re-
flectors localized near the mirrors on the main aisle are essential.
A 60-watt lamp with bowl-shaped dense opal reflector between
pairs of mirrors proves satisfactory.
The night view in Fig. 13 shows a locker room with single tier
lockers in which general illumination is provided. The finish is
dull gray throughout. Sixty-watt clear tungsten filament lamps
in flared prismatic reflectors22 are placed close to the 11 ft.
3.35 m.) ceiling on 8 x 14 ft. (2.43 x 4.26 m.) centers, giving one
half watt per sq. ft.
Running Track. — In most cases this extends around the main
exercising room, but the one at Columbia University is some-
what longer than the average and the major portion is in the
form of a rather low tunnel 10 ft. high by 11 ft. wide. Glaring
light sources would prove very objectionable here so 60-watt
clear tungsten filament lamps are used in 12 in. opalescent glass
semi-indirect dishes31 on 28- ft. (8.53 m.) centers.
Wrestling, Boxing and Fencing Rooms. — The finish is fre-
quently light and the ceiling smooth ; the room is often decorated
with prizes, pennants, etc., so the decorative element of the light-
ing becomes of more importance. The indirect systems are quite
applicable.
A description of the fencing room at Columbia University will
illustrate a typical case; the dimensions are 26 x 38 ft. with a
14 ft. white ceiling; two outlets are provided and 400 watt gas-
filled tungsten filament lamps in leaded white glass semi-indirect
dishes32 20 in. in diameter furnish very satisfactory illumination.
The energy consumption is 0.8 watt per sq. ft. actual compara-
tive 1. 14.
Medical Director's Office. — This room has the ordinary require-
ments for office lighting, providing plenty of light in all parts of
the room for physical examinations. Totally indirect lighting
is employed in quite a number of the installations visited, averag-
ing approximately one watt per square foot.
Squash Court. — These are usually rectangular in shape and ap-
proximately 15 x 30 ft. (4.57 x 9.14 m.) in size. Many have
white ceilings which will permit the use of totally indirect or
POWELL AND ODAY: ARMORY AND GYMNASIUM LIGHTING 757
semi-indirect lighting. Since the walls are finished in dark red,
an imitation of mahogany, quite a high wattage will be required
with either of the above systems. The Squash Club of New
York is experimenting, at the present time, with semi-indirect
bowls and gas filled tungsten filament lamps. The courts at the
Yale Club are equipped with porcelain enameled totally indirect
fixtures. It is quite important to avoid glare and reflections from
the varnished surfaces.
Handball Court. — The board must be well lighted, and a rather
high component of illumination on imaginary vertical planes cov-
ering the whole area of play should be provided, as it is necessary
to see the ball in its travel. The angle type reflector meets these
conditions excellently, completely shielding the eye, for the player
is always looking forward. The courts at Columbia University
are 24 x 21 ft. (7.31 x 6.40 m.) with a 13 ft. white ceiling. Two
250-watt lamps are placed on each court close to the ceiling in
angle type porcelain enameled steel reflectors,33 giving slightly
over one watt per sq. ft. for the effective area.
In the Newark Y. M. C. A. the board is located below the
running track and is especially lighted by 25 watt lamps in half
hand metal shades on the under side of the track, spaced on 4-ft.
centers. The general illumination of the room is adequate when
one is playing back.
Trophy Room. — This is usually quite elaborate and decorative
lighting systems are desirable. On account of the variety of
decoration, it is inadvisable to present any average figures.
ACKNOWLEDGMENT.
The authors express their appreciation of the assistance in the
compilation of the paper rendered by the members of the De-
partment of Water Supply, Gas & Electricity of the City of New
York, Mr. G. B. Nichols, chief engineer of the New York State
Architect's Office and Messrs. G. H. Stickney, R. E. Harrington
and E. F. Carrington of the Edison Lamp Works.
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POWELL AND ODAY : ARMORY AND GYMNASIUM LIGHTING 759
APPENDIX III.
i. Holophane Realite 06260 V. S.
2. Holophane prismatic reflector XE-500.
3. Holophane prismatic reflector XL250.
4. Benjamin fixture 6158.
5. Holophane Sudan reflector 1224-16".
6. Holophane prismatic reflector XE-100.
7. Benjamin fixture 6124.
8. G. E. Novalux form 1 157078.
9. Benjamin fixture 6179.
10. Benjamin fixture 6199.
11. Wheeler multiple Mazda fixture 2702.
12. Frink mirrored reflectors, marketed by the H. W. Johns-Manville Co.
13. Ivanhoe metal reflector AL-60.
14. Holophane pendant ball 3063.
15. Holophane Stalactite 3354.
16. Ivanhoe metal DED-250.
17. Benjamin flat cone 5503.
18. Ivanhoe metal DED-150.
19. National X-Ray Beehive 765.
20. Ivanhoe metal BEI-500.
21. Luna reflector 14, made by the H. Northwood Glass Co.
22. Holophane distributing reflector 6072.
23. Doric hemisphere 1234, marketed by the Lighting Studios Co.
24. Ivanhoe promotion fixture 758.
25. Holophane prismatic reflector XE-150.
26. Holophane glass reflector 2633.
27. Mazda Monolux diffuser unit 1329.
28. Holophane Sudan glass reflector 01225-10".
29. National X-Ray reflector E-60.
30. Holophane Druid glass reflector 3024-10".
31. Camia dish, marketed by the Opalux Co.
32. Mazda Monolux fixture 3320.
33. Ivanhoe metal REL-250.
760 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
DISCUSSION.
Mr. G. B. Nichols : Mr. Powell's paper on armory and gym-
nasium lighting appears to have come before this Society at a
very opportune time, in that probably within the next year there
will be a large number of armories started throughout the coun-
try, following up the movement of increasing the facilities of the
armories, which has been advocated since the European War.
This paper I believe to be very complete in obtaining the latest
data on the armories throughout the East, in which the latest
equipment has been installed. The paper will also be of consid-
erable interest in designing the equipment for the new Eighth
Regiment Coast Artillery, referred to in the paper as being the
armory with 180,000 square feet of floor area in the drill shed,
which is probably the largest armory that will be constructed in
this country for a considerable period. The size of this armory
can be conceived, when we say it is three and one half times the
size of Madison Square Garden.
In the lighting of armories, as brought out in the paper, con-
siderable attention should be paid to the character of the floor,
for in armories designed for calvary use, generally some form
of tan bark is installed and, on account of the absorbing qual-
ities of this material, double the foot-candle intensity will be re-
quired to obtain the same lighting effect. Up to four years ago
the majority of armories of New York State were lighted by
incandescent and gas lamps and, in a few cases, by arc lights. At
this time considerable study was carried on, particularly in New
York City, to determine the advisability of installing flame arcs
and a number of installations were made at that time. It is to
be regretted that these installations, which have been in use such
a short period, should now be supplanted with incandescent
lamps of the gas-filled type.
One of the armories mentioned in the paper, namely, Troop C
Armory in Brooklyn, which is one of the newer armories in New
York, during the last four years has had three different types of
lighting units installed in the riding ring. Originally there were
114 enclosed arc lamps. Three years ago this installation was
changed to flaming arcs, 14 having a total wattage of approxi-
mately 18,000 watts being installed. In this installation the
ARMORY AND GYMNASIUM LIGHTING 761
average foot-candle intensity for the entire room was 3.6; the
maximum was 5.5, and the minimum 1.2. The 1.2 readings,
however, were at the very outer edge of the riding ring and are
of slight importance. The watts per square foot figure was 0.093.
The estimated cost of lighting for this armory for one year, in-
cluding maintenance for this installation was $1,348.55.
A year ago this installation of flame arcs was removed and
gas-filled, incandescent lamps were installed, which installation
is the one mentioned in Mr. Powell's paper as having a total
wattage of 22,500 watts. Photometric readings showed the fol-
lowing intensities: average 3.24, maximum 4, minimum 1.82.
Watts per square foot 0.129. The estimated total cost of lighting,
including maintenance per year and lamps replaced, is $1,235.23,
being a slight decrease from that of the flame arc installation.
On comparing the two systems, the slight difference in annual
cost is very little importance, the main feature being to decide
the relative merits of the two installations. The consensus of
opinion was that the gas-filled lamps are preferable to flame arcs
for the following reasons :
1. Colors are not distorted to such an extent under the gas-
filled lamps. This is particularly objectionable where the arm-
ories are used for dress occasions, where there is considerable
objection to having the colors of the uniforms very much dis-
torted.
To add to the information given in the schedule, I would state
that photometric tests have been made on the following armories :
Troop C, 3.24 foot-candles; 10th Regiment Armory, Albany,
2.32 foot-candles; 47th Regiment, small shed, 1.46 foot-candles.
It appears that the 47th Regiment lighting should be increased, as
this installation was not designed for the equipment now in-
stalled.
I would also call to your attention the State Armory at Albany,
mentioned in the paper, which is typical of what might be done
in an armory already lighted by incandescent lamps. At this
armory, two gas-filled lamps were installed in place of a lighting
fixture containing eight 250-watt tungsten lamps. The old fix-
tures were simply taken down and new ones installed in their
place, with two lamps at each outlet, the fixtures simply being
762 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
suspended by wire cables from the overhead trusses, making a
very inexpensive outfit. This change could be made at almost
any armory at a slight extra expense, which would probably be
saved during the first year.
Considerable improvement I believe is possible in the method
of trimming. At the present time the most practical way seems
to be to trim by extension ladders, which is done with consider-
able difficulty, the lamps being generally about 35 feet from the
floor. As yet no successful lowering device of moderate cost has
been developed.
In reference to gymnasium lighting, I would state that in my
judgment the values given in the paper are the minimum rather
than the average for good lighting. In discussing this form of
lighting with gymnasium instructors, it appears to be the con-
sensus of opinion that the illumination should be very high and
well distributed, on account of the vast work being carried on.
In some gymnasiums the foot-candle intensities run as high as
6, which is not excessive.
Would it not be possible to reach the lighting equipment in an
armory from a walk-way constructed in the trusses in the roof
and thus eliminate the necessity of lowering the lamps ? It would
seem that the girder construction and wide spacing of a few
large units would make this not only possible, but probably most
advisable. I believe the Colesium in Chicago has such an ar-
rangement, with a main walk-way lengthwise of the building,
protected by a pipe hand-rail on either side and branch walk-
ways crosswise the building.
Mr. L. C. Porter : Reference has been made in this paper to
the lighting of rifle ranges. This is a subject which warrants a
great deal more study than has been given to it. The ultimate
aim of this indoor practise is to teach a man to shoot out-of-
doors, to handle a rifle, to load, to pull the trigger, to properly
sight, etc. In most rifle ranges the conditions are vastly differ-
ent from what they are out-of-doors. It is very common to have
the target highly lighted and the space between the targets and
the shooter entirely dark; sometimes there is enough light to en-
able the shooter to load the gun. Experiments which have been
undertaken seem to indicate that it may be better practise to have
ARMORY AND GYMNASIUM LIGHTING 763
some illumination between the man and the target, thus at least
approximating a little more closely outdoor conditions.
One method that has been successfully tried to accomplish this
is by the use of flood lighting, by projecting a beam of light from
behind the shooter onto the target. There will be enough stray
light to give some illumination the entire length of the gallery. Of
course, in this case care must be taken that the target does not
reflect the light specularly back to the shooter.
Mention has been made of the Yale gymnasium ; being a Yale
man myself I have done some work in that gymnasium and I
think that one word of caution should be given to those who are
working on gymnasium lighting. It seems to me that it is neces-
sary to have light of high intensity in gymnasiums, especially in
ring work and bar work. However, it is of extreme importance
to have it well diffused ; under no circumstances should a glaring
light source be used. There are many times when a man is fac-
ing the ceiling and the light source, and in tumbling and ring
work, as has been mentioned, it is necessary for him to see very
quickly, to catch the flying ring. In such cases glaring light
sources may result in serious accidents.
Mr. R. B. Ely : I should like to ask Mr. Powell as to his ex-
perience with lamps used over swimming pools, whether he ever
uses enclosing globes. I think enclosing globes would take care
of and eliminate the danger of exploding and broken lamps. The
broken glass may be the cause of accidents.
I know of a case where a man brought suit for having one of
his patrons cut by a piece of glass in the bottom of the swimming
pool, and another instance where a young man started to fool
with a lamp and accidentally touched the base and was killed.
Mr. A. L. Powell : One of the gentlemen, who has discussed
the paper, mentioned that the intensity of illumination in the 23rd
Regiment Armory, Brooklyn, was somewhat low. An examina-
tion of the data presented shows this to be undoubtedly true, for
there is but 0.25 watt per sq. ft., whereas the average value is
approximately 0.5 watt per sq. ft. using the gas-filled tungsten
lamps. This average value, we believe, will give satisfactory
results under ordinary conditions.
It was suggested that a platform or run-way be built among the
764 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
roof trusses, from lamp to lamp, instead of providing lowering
devices. One speaker pointed out the greatly increased invest-
ment necessary to build a platform strong enough, and the safety
factor must also be very carefully considered, for in most in-
stances the iron work is from 50 to 100 ft. above the ground.
Floodlighting may be of use for those rifle ranges with no ob-
structions, but in some galleries the construction is such that this
type of lighting would be impracticable. These particular cases
are arranged so that but one target can be seen from the gun posi-
tion. This is done by placing partitions or shields at points along
the gallery, with apertures in the line of the target acting in the
same manner as the light screens on a standard photometer bar.
One has to be directly in line with these series of holes in order
to see the target, else all that is visible is the black shield (see
Fig. 6.) A projector unit would not serve in this case unless
there were one for each target.
Other speakers called attention to the fact that data were pre-
sented on a number of gymnasiums which were far from very
well illuminated, as indicated in the minimum values given. This
is indeed too true, particularly in reference to those exercising
rooms listed in Table 1, and as is stated in the paragraph above
this table, it is to be hoped that these conditions will be remedied.
There is a large field open for improvement in this class of light-
ing. It can be seen that quite a number of gymnasiums were
visited and those described under Appendix 2 represent the best
conditions met as far as proper equipment and suitable intensity
of light are concerned. Even in this table there are but few ex-
amples of what might be termed the best lighting.
The authors' attention has never been called to the danger of
broken glass from the lamps about swimming pools and in locker
and wash rooms. In none of the gymnasiums visited was there
any special provision made to protect the lamp from water
and to prevent glass falling to the floor. It does not seem that
there should be any more appreciable danger in walking about
these rooms in one's bare feet than in walking about the bath
room in the home which is ordinarily lighted by a standard type
of fixture and incandescent lamp.
Mr. G. B. Nichols: In reference to the breakage of lamps
ARMORY AND GYMNASIUM LIGHTING 765
and globes in swimming pools, this breakage has not been of any
great importance, unless in swimming pools where games are
carried on, which are likely to break the globes. In these in-
stances, it seems preferable to install some form of wire cage
over the fixture. I believe, however, that these conditions can
be met to a considerable extent by using some form of metal re-
flector; the breakage of the lamps is not a serious matter.
766 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
PRACTICAL HINTS ON THE USE OF PORTABLE
PHOTOMETERS.*
BY W. F. LITTLE.
Synopsis: This paper outlines a desirable procedure in the conduct
of photometric tests with portable apparatus. It discusses the planning
of a survey; a description of the condition of the installation and pre-
cautions which should be taken to make the results useful; a method of
testing candlepower, illumination intensity and brightness; good practise
in the maintenance of photometric apparatus ; photometric errors inhering
in photometers and accessories, together with means of avoiding them;
photometric accuracy and test results.
In the use of portable photometers the same photometric prin-
ciples prevail as in the operation of stationary or laboratory types
of photometers ; indeed, a portable photometer is no more than
a stationary photometer reduced in size and with a test-plate sub-
stituted for one of the photometric surfaces. The only principle
peculiar to the use of portable photometers is, therefore, that of
the cosine law as applied to the test-plate.
The practise of photometry as applied to portable photometers
differs radically from that followed with stationary photometers,
in that the conditions of use are not standardized, the purpose
and the method of test are usually not so definitely indicated, and
the practitioner is often less experienced. Also, the auxiliary
instruments used in connection with portable photometers are
frequently less accurate than those used with stationary pho-
tometers.
These differences, in combination, contribute to surround the
use of portable photometers with a liability to error which is
greater than that experienced in the use of stationary photometers.
The successful use of portable photometers demands more exer-
cise of good judgment, and a more general knowledge of photo-
metric principles and practise than is usually required of the
photometrist in routine laboratory work. In view of these facts
it has been thought desirable to present the results of the writer's
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, I9I 5-
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
LITTLE: USE OF PORTABLE PHOTOMETERS 767
experience in the use of portable photometers, making it avail-
able to others who may engage in this class of testing.
AN ILLUMINATION SURVEY.
In the conduct of an illumination test the first fundamentally
important consideration is to arrive at a correct understanding
of the purpose of the lighting installation and of the purpose of
the test. It is then important to determine whether the installa-
tion tested is representative and whether the samples or sample,
if only a portion of the installation is tested, are typical of the
whole. The test should be so planned and described that there
shall be a minimum of danger that any incorrect conclusions will
be drawn. These statements, though generalities, may be applied
in specific cases and when applied will contribute to the useful-
ness of the data obtained through illumination tests.
DESCRIPTION OF INSTALLATION AND CONDITIONS.
The photometrist's note-book should contain a full description
of the important features of the installation including the con-
dition of pressure or voltage and consumption, the condition of
illuminants and other accessories with special references to their
suitability for the service, their cleanliness and age; variables
affecting the test as, for example, pressure fluctuations with arti-
ficial illuminants, change in sky brightness in daylight tests, etc. ;
description of the environment including dimensions, finish and
location of light sources in indoor, and corresponding descriptions
in outdoor tests. The refinement to which this description is
carried must, of course, depend upon the nature and purpose of
the survey. When the measurments are of illumination inten-
sity or brightness, the description should include a statement of
the total flux and of the distribution characteristic of the light
source.
The description should give very specifically the location of
the installation under test so that it may be readily identified and
conditions duplicated at any time. It should have in view the
purpose of affording a basis for intelligent discussion of results
after the tests are complete.
OPERATING DATA.
It is important to measure the pressure and consumption values
768 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
of the illuminants. From such data deviations from standard
initial operating conditions can be allowed for.
TESTS OF CANDLEPOWER.
Location of Photometer. — It is to be presumed that in measure-
ments of candlepower a certain angle or series of angles in a ver-
tical plane is stipulated for investigation. It is important to
know whether or not the source tested has symmetrical distribu-
tion at such angles. If not, care should be taken to select a di-
rection in which the intensity is the mean for the angle investi-
gated. If this is not feasible the tests should be made in a num-
ber of directions. It is good practise where a second photometer
is available to make simultaneous tests on opposite sides of the
illuminant.
Stray Light. — An important step which should be taken in
preparing for measurements of candlepower is the proper screen-
ing of the photometer against stray light. A portable photometer
is likely to be used in the measurements of candlepower else-
where than in a well equipped laboratory where all proper ar-
rangements are provided. The conditions for the test are likely
to be improvised and the need for proper precaution against stray
light is, therefore, the greater. It is important to look from or
through the photometer toward the light source and make certain
that no other light source illuminates the test-plate, and that no
surface reflects an appreciable amount of light upon it. A sim-
ple procedure is to introduce a suitable lens between the pho-
tometer device and the light source which will enlarge the field of
view permitting the easy examination of the entire field. Most
portable photometers are equipped with one or more screens
near the test-plate which limit the area to which the test-plate
is exposed. Frequently, however, additional screens are neces-
sary to cut off all stray light.
Alignment of Photometer. — The tubes carrying the test-plate
of the photometer, and the screens, limit the light falling on the
test-plate, so that the photometer can be aimed directly at the
lamp. If the test-plate employed is placed across the angle of
the tube so that the rays fall upon it at 45 °, the position of the
test-plate is particularly important. Unless suitable facilities are
provided, much time may be consumed in properly aligning a
little: use; of portable photometers 769
photometer in candlepower measurements. A method which ex-
perience has shown to be convenient consists in the use of
the elbow tube of the photometer with a simple telescope and
cross hairs described elsewhere. With a protractor and plumb
bob attached to such a telescope a ready means of determining the
height of the lamps is at hand, also its distance from the photom-
eter may be determined. The protractor also affords a quick and
accurate measurement of the angle between the vertical and the
direction of light, without the necessity of accurately leveling the
photometer.
Test-plate. — Both reflecting and transmitting test-plates are
used in candlepower measurements. As the subject of test-plates
is to be discussed before this convention in another paper1 the dis-
cussion in this connection will be limited. The test-plate set at
45° to the rays of light suffers under the disadvantages of requir-
ing more accurate alignment, but has the advantage of being more
easily screened and of rendering a brighter field.
Calculations. — In the conduct of candlepower tests it is of
course necessary to know the angle of measurement and the dis-
tance between the lamp and the photometer.
Computations may be based upon the following :
C.P. =F.C.X</21
d2 = A2 + b2
d-
b \2 \ Fi§-
Vsina/ J
LAMP
PHOTOM
To determine h where the height cannot be measured directly,
a base may be laid off and from the angle determined, h can be
computed.
LAMP
h = a Tan. /? Fig. 2.
"* AT
The photometer may be located so as to measure any angle by
1 Sharp, C H., and Little, W. F., A compensated illumination test-plate.
770 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
first determining the height and then laying off the proper base.
Tan. a
b=— IT
In all computations it is to be remembered that the distances
are measured vertically, and horizontally, and they are determined
with respect to the test-plate and not the floor or street level.
Means of determining street grades and exact location of
lamps are discussed later.
The signs and tangents are used in the above formula as they
may be read directly from a slide rule.
ILLUMINATION MEASUREMENTS.
It is obvious that illumination measurements should be made
in a plane, the illumination of which is the principal purpose of
the installation. This refers to height of horizontal plane or to
inclination of other planes which may be studied. In some cases
it may be desirable to determine the flux density of the light
incident on a surface inclined to the horizontal. As in the case
of the study of the illumination of school desks, show windows,
machinery, etc.
During the test it is very essential to record service conditions
simultaneous with the photometer readings; for example, the
voltage should be noted for each reading or the averaging voltage
for a series of readings. With the data and the characteristic
curves of the illuminants the measurements may be corrected to
the standard condition (Fig. 3).
Selection of Test Stations. — Practise in the selection of test
stations falls into two general classes : in the one the purpose is
to determine the total flux of light on a given plane and to employ
this value to determine the illumination efficiency of the installa-
tion. In the other the purpose is to determine the flux density at
important points without the intention of making a compete study
of the installation. Each practise has its own field of usefulness.
If irregular or special locations for test stations are selected
it is usually impracticable to arrive at a figure for the illumination
efficiency.
In the writer's work it has usually been desirable to make the
more complete study of an installation from which the efficiency
may be determined, and the practise has been to select syste-
LITTLE : USE OF PORTABLE PHOTOMETERS
771
matically arranged test stations, and to supplement them by such
measurements as may be desired, at points of special significance.
In such practise it is customary to divide the floor space beneath
the illuminants into equal areas, the illuminants being over the
intersection of boundary lines of such areas rather than over the
centers of the areas. Fig. 4 illustrates such a layout for a bay
illuminated by four lamps). The numerical average of the hori-
zontal illumination intensities for test stations so disposed will be
the mean flux density for the entire plane if a sufficient number
of test stations are selected. For the construction of illumination
95 96 97 96 99 100 101 102 103 104- 105
curves, and for further information regarding the uniformity
of the lighting, it is usually desirable to supplement these regu-
larly spaced test stations by other measurements made perhaps
directly beneath lamps, at points where a minimum intensity is
anticipated, and at other points of special interest. Measure-
ments directly beneath the lamps also afford some indication as to
the rating and the uniformity of the lamps.
Photometer Test-Plate. — As has been indicated the test-plate
is the one elemental feature which differentiates the portable
photometer from the stationary photometer, or the illumination
photometer from the candlepower photometer. It is also the one
feature of a photometer in which a known systematic error has
existed. The reference is to the departure of the brightness char-
772 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
acteristic of the test-plate from Lambert's cosine law. This
error has been tolerated because no simple and adequate means
of avoiding it have been available. In the compensated test-
plate described in another paper1 this error is eliminated.
The error of the transmitting test-plate differs from that of
the reflecting test-plate in that for a given angle it is constant for
all directions of incident light because the surface is always
viewed normally. The error of the reflecting test-plate likewise
varies with the angle, and for any given angle may vary with the
azimuth or the direction of light. In the cases where the reflect-
ing test-plate is viewed normally one of these variables is
eliminated.
Fig. 6.— Plumb-bob suspended from center of an opaque ring.
With the transmitting test-plate the photometer and the ob-
server may be located below the plane of illumination and may,
therefore, avoid shadows upon the plane. When a reflecting test-
plate is employed it usually is difficult to avoid casting shadows
upon the plate. The obvious procedure is to choose the direction
of view which will minimize the obstruction of light on the plate,
by the photometer and observer, having due regard to the selection
of the angle of view which will avoid large errors due to the de-
parture from cosine law.
The reflecting test-plate may be used to good advantage in
inaccessible places, such as show cases, walls, ceilings, shelves,
packing cases, letter files, etc.
In the extended study of illumination on a given plane it is
i Trans. I. E- S., No. 8, vol. X, 1915.
•
^ "> <7
1
1' !
x» |
*?? '
x^ :
x-
y* :
x? :
;--
;
*■ ;
x»
<H
*}►>>•
Nei*>\^
Fig. 7.— A self-leveling test-plate.
"** ' Fig. 8.— Protractor, plumb-bob and level. Fig. 5.— Ammeter rheostat and dry cells.
LITTLE: USE OF PORTABLE PHOTOMETERS 773
necessary to establish a level for the test-plate and maintain it.
This is a simple matter in interiors where a level floor may be
relied upon. In other cases, such as street lighting where the
level has to be re-established at each station, and a reflecting
test-plate is employed, a self -leveling test-plate is a great con-
venience.
Associated Candlepower Measurements. — Where a complete
knowledge of the facts is desired, an intelligent discussion of
results is impracticable if the light flux produced by the sources
is unknown.
BRIGHTNESS.
Many installations may prove thoroughly satisfactory in that
the intensity is all that is required, and the uniformity good,
but there may be objects reflecting specularly or brightly il-
luminated areas within the immediate line of vision, which
make the result objectionable and fatiguing to the eyes. It
is frequently found of considerable aid in studying an installation
to measure the brightness of the various objects within the ordi-
nary line of vision. It is sometimes advisable to measure the
same object in the plane of incident light, and in a direction
900 removed from the plane of incident light; in other words,
measure the brightness in the direction of highest intensity
and lowest intensity. The percentage difference will afford some
indication of the potentialities for glare due to specular reflection
from objects, such as a polished top desk, glossy paper, etc.
The brightness of the glassware surrounding the illuminant
and ceiling or wall against which it is viewed can be measured,
and the data obtained may represent the characteristics of the
installation from the standpoint of great and annoying contrasts.
The approximate reflecting qualities or any mat surface can
be ascertained by comparing the brightness of the surface with
the brightness of a reflecting test-plate. The reflection coefficient
of the test-plate is known, therefore, the reflection coefficient of
the surface may be computed.
Brightness Measurements. — To make brightness measurements
with a portable photometer the plate is eliminated and the surface
to be measured is viewed directly. In other words, the surface
to be measured is one of the photometric surfaces to be compared
with the standard surface in the photometer. The brightness of
774 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
a uniformly illuminated surface as indicated by the photometer
scale is independent of the distance between the photometer and
the surface. This is obvious as the brightness of a surface does
not vary with distance. Also as the distance between the photom-
eter and the surface increased so does the area viewed in the
photometer increase.
Brightness may be expressed in Lamberts.2
L = Lamberts
F = Flux
S = Area in sq. cm.
MAINTENANCE OF PHOTOMETER.
The photometrist should satisfy himself as to the correctness
of the constants of the photometer before employing it in serious
work. The adjustment of the comparison lamp, the transmis-
sion of the absorbing screens, and the accuracy of the scale
throughout its entire range should command his particular atten-
tion. This cannot be done unless there is available an adequate
equipment for verifying the instrument. Such an equipment is
essential not only for a first check of the instrument but must
be on hand if maintained accuracy is to be had throughout the
life of the instrument. Comparison lamps will change and the
optical parts of an instrument may become dusty through inatten-
tion. The only efficient safeguard is to provide independent
means of verifying the photometer.
Among means for verifying photometers are small standard-
izing attachments for the simple check of the instrument in ser-
vice at one point on the scale. Such a check is, however, quite
incomplete unless an independent means is employed for the
electrical measurements. To use the same electrical instruments
for the photometer lamp is not good practise. For a verification
of the other constants of the instrument more elaborate means
must be provided.
The absorbing screens may be checked approximately at any
one time during a test by finding some point where a fairly con-
stant illumination can be had of such intensity that it may be
2 See 1915 report of the Committee on Nomenclature and Standards of the I. E. S.
UTTLE: USE OF PORTABLE PHOTOMETERS 775
read both with and without the screen. In case of the use of
two or more screens a darker screen can be verified by securing
some other illumination which may be read with first the light
screen and then the dark, thus securing the values for one screen
in terms of the other.
ACCESSORIES.
There are a number of accessories to a portable photometer
some of which are necessary, others simply convenient or con-
ducive to greater accuracy. A few of these accessories are cited
below, divided into two groups, essentials, and those conducive
to greater accuracy.
Essentials Aids to convenience or accuracy
Note-book Standardizing equipment
Batteries or other supply Self leveling test-plate
Electrical instrument Color screens
Tripod Telescope and cross-hairs
Plumb-bob Protractor, plumb-bob and level
Tape Slide rule
Chalk
Note-Book. — The keeping of a photometrist's note-book is very
important, as in many cases the small details which are often
overlooked are of vital importance in the discussion of results.
An aid to this end is a blank form divided into numerous head-
ings and to be filled in during the test. The following is a sheet
from a photometrist's note-book (see Fig. 4). The note-book
page should be ruled in cross section as an aid in making maps.
Electrical Instrument. — All modern portable photometers em-
ploy electric comparison lamps. They must be kept at the stand-
ardization values if the work is to be accurate. It is a character-
istic of the tungsten filament lamp that 1 per cent, variation in the
impressed voltage occasions a change in candlepower of about
5 per cent., and 1 per cent, change in the current occasions a
change in candlepower of about 10 per cent. Errors in indicating
electrical instruments used with photometers are therefore mul-
tiplied by large factors in the resultant photometric values. Thus
precision in the electrical instrument becomes very important.
Unfortunately, it is the current practise to employ with portable
photometers electrical instruments which in themselves are either
of insufficient precision or which in their use are not handled with
776 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
sufficient care to obtain proper precision. It is to be feared that
many illumination measurements suffer in consequence of this.
It is conservative to say that an accuracy of 0.2 per cent, ought
to be attained in voltmeters or ammeters used in portable work.
Most portable voltmeters and ammeters are not compensated
for temperature changes sufficiently for work where extremes of
temperature prevail. If photometric equipment is to be used in
such cases the temperature of the indicating electrical instrument
should be determined and the corrections should be applied. An-
other source of error encountered through the use of electrical
instruments is that due to the influence of stray fields or the
shunting of the instrument field. Care should therefore be taken
to avoid placing the instrument on or near magnetic metals, such
as resting the meter on the floor or sidewalk over iron beams.
With the usual portable voltmeter and ammeters 0.2 per cent,
accuracy can be obtained only if the error of the instrument is
known and the instrument is handled and read most carefully.
Different portable photometers require different potentials for
their operation, but the majority use a low volt comparison lamp
(3-6 volts) which may be operated on either a small storage bat-
tery or on dry cells. If the lamp does not require more than 0.2
to 0.3 ampere dry cells will be found very satisfactory, and for
convenience the screw top cell is preferable. As a measuring
instrument a well compensated ammeter is preferable to a volt-
meter as the photometer leads can be as long or as short as con-
venience requires without changing the electrical values in the
lamp, Fig. 5. In some photometers the regulation of a compari-
son lamp is accomplished by means of a Wheatstone bridge. The
resistance of a tungsten filament varies with the temperature.
With three fixed arms in the bridge and the lamp for the fourth,
the bridge will balance only when the lamp is at the proper resis-
tance or the proper current is passing through the lamp. This
device may be used as an accessory or part of the instrument. If
as an accessory it must be attached to the photometer so that there
is a minimum of wire of low resistance between the device and the
lamp, thus obviating errors due to change in temperature of the
leads. A low resistance galvanometer or low resistance high
sensibility telephone may be used with excellent results as an in-
LITTLE: USE OF PORTABLE PHOTOMETERS JJJ
dicator for securing a balance. With sensitive galvonometer
changes in current may be detected to less than 0.01 of I per cent.
Tripod. — A great deal of the work in which a portable photo-
meter is required is done with the photometer mounted on a
tripod, the measurements being made in a given plane. As the
photometer is moved from station to station it is not convenient
to re-level each time. Therefore a tripod with rigid legs is most
convenient. For street work with uneven surfaces, however, it
is essential that the legs be adjustable.
Plumb-bob. — In any photometric measurements where it is
essential to establish test stations having a definite location with
reference to the light source, it is necessary to establish accurately
a point immediately beneath the source. A quick method is the
use of a plumb-bob suspended from the center of an opaque ring.
To determine the point directly beneath the light source the plumb-
bob must fall in the center of the illuminated area of light falling
through the ring or at the center of the shadow of the ring (see
Fig. 6).
Tape. — For computations a tape divided in tenths and hun-
dredths of feet is found very helpful.
AIDS TO CONVENIENCE AND ACCURACY.
Standardising Equipment. — As previously stated photometers
must be frequently verified, and a small standardizing equipment
for portable photometers furnishes a verification during test.
This equipment, of course, must be verified itself, but as it is used
for only a small fraction of the time that the photometer is used,
it should remain constant for a long period. These standardizing
equipments may be either self-contained, using the Wheatstone
bridge principle, or may make use of the energy supply and meter
used for the photometer. This later method has the disadvantage
of rendering inaccurate results, if there is any change in the in-
dicating instrument.
Self -Leveling Test-Plate. — For horizontal illumination values
where a level floor or street are not available the self -leveling test-
plate proves a great time saver. In case of high winds this de-
vice is equipped with a lock, but when the lock is used care should
be taken to relevel the test-plate at each station. Fig. 7.
Color Filters. — Photometric accuracy depends largely upon a
778 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
close color match between the test and comparison field and an
aid in promoting accuracy in measuring illuminants of a different
color than the comparison lamp is a set of color filters. While it
is difficult to match every light source, an approximate match
can be secured with a few filters. The transmission values of
these filters should be determined by comparison with standard-
ized filters, and wherever practicable the filters should be placed
between the comparison lamp and the photometer head. Thus
a known flux of light is allowed to pass regardless of the color
components of the test source. The objection to the use of color
filters on the test side of a photometer however is more theoreti-
cal than practical.
Telescope. — Cross Hairs. — A simple short focus telescope with
cross hairs forms a convenient apparatus for aligning the photom-
eter. This can be made either a part of the photometer optical
system or be mounted adjacent and parallel to the optical system.
Protractor and Plumb-Bob and Level. — The convenience of
this device has been discussed in the determination of angles for
candlepower measurements. It is also an aid in establishing
street levels and street grades as well as securing building heights,
tree heights, etc. (Fig. 8).
DISCUSSION OF RESULTS.
When a survey has been completed and the time comes to draw
conclusions from the test data there are a number of consider-
ations which it is well to remember. In the first place the purpose
of the survey should be kept clearly in mind and the photometrist
should be satisfied that the measurements are such in number and
time as will accomplish this purpose. It is important to be sure
that the measurements have been made in the plane or planes
whose illumination is important; that the installation is typical
of any installations which the conclusions may affect; that the
operating conditions are typical and, in general, that there is
no reason why the indications of the test should not be taken at
their face value.
Test results invariably are subject to errors or to deviation
from absolute accuracy. Each element which contributes to the
final result possess liability to error. The photometer, the elec-
trical instrument, the observer, each departs from absolute ac-
LITTLE: USE OF PORTABLE PHOTOMETERS 779
curacy, and the individual errors combine to constitute the error
of the final result. The procedure, therefore, is to ascertain or
estimate the extent of such individual errors, and to make certain
that no errors are present in the final results which are large
enough to vitiate the conclusions. Before results are accepted
the accuracy of the indication of the photometer with the instru-
ment with which it has been used should be determined to a
certainty, and it is good practise to recalibrate the photometer
with its electrical instruments after as well as before the test,
in order to obtain assurance on this score.
In work of this class there are so many possibilities of error
that all reasonable means ought to be availed of to check the
results. No opportunity should be neglected to compare measure-
ments with those obtained with another equipment. Experience
with tests in similar installations should be brought to bear to
ascertain if the results appear reasonable. Where the flux pro-
duced by the lamps has been ascertained, and illumination meas-
urements have been made on a particular plane, the ratio of
flux delivered to flux produced should be computed in order to
determine if the ''efficiency of utilization" appears to be reason-
able.
Finally when accuracy has been assured and conclusions are
drawn from a test, it is important to confine such conclusions to
the particular test under discussion. All that can be said without
qualification is that the result and the conclusions as obtained
apply to a particular installation, a particular set of operating
conditions, and a particular time. Before the conclusions may be
assumed to be applicable to any other installation, any other set
of operating conditions or any other time, assurance must be had
that no differences exist which would alter the results in any
particular capable of changing the conclusions.
DISCUSSION.
Mr. W. A. Durgin : Those of us who are more or less in the
business of selling illumination which shall be permanently satis-
factory are very glad to have this sort of paper published. Illum-
ination questions are much befogged by assertions and discussions
based on readings made by some inexperienced person with a
portable photometer borrowed over night from a central station
780 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
company or other unwilling accomplice. It is to be hoped that
this paper will give much publicity to the need of specialized ex-
perience and skill, if data of any real value is to be secured.
A few accessories not mentioned in the paper have been found
helpful.
First in importance is a small truck similar to that shown in
Fig. 3 in Messrs. Harrison and Anderson's paper1 which is to be
read at this convention. We have used such a truck with
smaller casters for some time in all interior and side walk tests
and recommend it especially for the ease with which cross wires
on the base can be used to quickly fix the location at stations.
The arrangement is much more convenient than the usual swing-
ing plumb-bob.
Improved absorption screens offer another convenience. These
are available in sets having definite coefficients of 0.1, 0.0 1 and
0.001 transmission accurate to x/i per cent.; a notable advance
over the haphazard coefficients generally in use.
In standardizing the photometer, we obtain more consistent
results by leaving the current adjustment unchanged and deter-
mining from time to time the constant factor to be applied to the
foot-candle readings. The use of a factor presents another ad-
vantage since in important work we find it necessary to use
duplicate equipment with two sets of observers and, with cor-
rection factor standardization, the two sets of uncorrected ob-
servations are sufficiently different to prevent bias in reading.
Some discussion of the means of checking brightness co-
efficient perhaps would add to the great value of the paper.
There is considerable doubt in many testers' minds as to just
what brightness constant means at the photometer screen and as
to whether the same calibration correction constant applies to it
as to the foot-candle reading.
Mr. L. C. Porter: Mr. Little calls attention to the necessity
of accurate measurement of the current in standard lamps, and
I think that that should be emphasized a little more. We find
in our work that one of the great sources of error is in not getting
the standard lamp in our photometer to operate at exactly the
proper current value. Some tests which I have made indicate
1 Trans. I. E. S., No. 9, vol. X, 1915.
USE OF PORTABLE PHOTOMETERS
78l
that a change of about one one-hundredth of an ampere through
the standard lamp will result in something like a 20 per cent,
change in foot-candles read on our photometer. The accompany-
ing curve shows a calibration test run on one lamp.
"92 94 96 98 100 I0Z 104 106 108
PERCENT. NORMAL AMPERES ON PHOTOMETER LAMP
Calibration curve of a portable photometer.
We have found that it is hardly practicable to hold the voltage
on the photometer lamp. The voltmeter leads are soldered to
the lamp socket and even with correct voltage there the lamp may
not be operating correctly, due to contact resistance between the
lamp base and the socket. It is more accurate to read amperes,
and in order to do that we use a mirrored needle milli-voltmeter
with a scale divided into 150 divisions, and a six-tenths ampere
shunt. In that way we can obtain a very accurate current value,
and changing the leads used does not entail a voltage drop, con-
tact resistance, etc.
Speaking of the use of dry batteries— we use dry batteries a
great deal for working portable photometers, but find that almost
every time the batteries are moved we have to re-set the milli-
voltmeter. After the lamp has burned a short time, the batteries
seem to hold fairly steady for a considerable length of time, if
not moved, but if the batteries are moved, it seems to affect the
current and we have to make readjustments.
782 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Another field in which portable photometers are being used to
a considerable extent is the measuring of searchlights, floodlights,
stereopticons, motion picture machines, etc. ; in fact, any pro-
jected light. That is very easily accomplished by two methods:
a searchlight may be set on a table which can be rotated ac-
curately; and the photometer held in one position or one may
draw an arc of a circle and measure off stations about a foot
apart across the beam of the searchlight and move the photom-
eter across the beam. In doing that, it is well to make sure that
the tube of the photometer points directly at the searchlight. It
can be easily located by taking off the diffusion plate on the end
of the tube and centering the searchlight in the photometer (one
can see it in the center of the mirror very clearly and can center
it in that way) then replace the diffusing glass and read the foot-
candle value. Multiplying that by the square of the distance
from the light source to the photometer, one obtains the beam
candlepower of the searchlight.
Mr. Earl A. Anderson : The discussion of the precautions
necessary in performing illumination tests with a portable pho-
tometer as given in this paper is of special value for, as Mr. Dur-
gin has suggested, very often portable photometers have been
used by individuals unacquainted with the necessary precautions.
Perhaps the first essential in reliable photometric work is careful
and frequent standardization of the comparison lamp. Where
stationary photometers are used, means for accomplishing this
are provided as a matter of course and for portable photometers
repeated calibration is even more necessary on account of the
more delicate nature of the apparatus and lamp, and the un-
avoidable jars and disturbances in carrying the instrument about.
Recognizing the importance of facilitating checks of the port-
able instruments the engineering department of the National
Lamp Works of the General Electric Company at Nela Park has
found it desirable to fit up a special photometric bench for this
purpose. A standard 125 in. bar is arranged with a device for
readily clamping into a fixed position at one end the illuminom-
eter which is to be checked. Standard lamps of high and low
candlepower are provided and the illumination can be conven-
iently varied over a wide range by altering the position of the
USE OP PORTABLE PHOTOMETERS 783
standard lamp carriage. Calculations are simplified by the use
of a distance scale calibrated to read directly in foot-candles upon
the test-plate.
A bench of this kind with the proper indicating instruments
in place enables the operator to take the number of observations
necessary for complete standardization of his instrument in a
very short period of time. In addition to the large saving in time
introduced, a permanent routine method for checking the port-
able photometer eliminates the doubt existent in test results
where standardization must be made with a temporary set-up.
Mr. S. L. E. Rose: It seems to me that one of the most im-
portant things here is the note-book and data taken during the
test. It is easy enough to watch the operator while he is in the
laboratory calibrating his instruments, and I don't think Mr.
Little's paper probably intended to cover the work done in the
laboratory; but when the operator gets outside, it has been our
experience that he will often come back with insufficient data to
properly interpret the results, and it is very advisable to have a
data sheet calling for what is wanted, and then all the operator
has to do is to fill in these blanks and when he gets back it is easy
enough to interpret the results. Another thing Mr. Little has
called attention to, which is important, is the experience neces-
sary to pick out the proper representative sections in the lighting
installation under test. Anyone with ordinary intelligence and
some instruction can take readings on a portable photometer;
but to go out and get the data properly noted down so that one
can have all the required conditions has been the greatest fault
we have found with the operator. Another great aid which we
have often used and which we have found advisable is, where
possible, to take a photograph of the installation. This will often
give a lot of data possibly not called for, and the operator has not
thought to jot down.
Mr. G. H. Stickney: From my experience and observation
of tests made with illumination photometers, I believe much data
is gathered, and some is published, in which indeterminate errors
exist. Such errors may render data worse than valueless, in
making it misleading.
I am somewhat apprehensive of tests made in interiors, especi-
784 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
ally with reflecting side walls, when the opaque test-plate is used,
since such plates must be observed from above. Even though the
observer may not cast a direct shadow on the test-plate, it is often
impracticable to tell whether or not an appreciable amount of
light, reflected from side walls or other objects, is being inter-
cepted.
Another source of error which, though small, may under some
conditions be sufficient to give misleading results, is the failure of
most test-plates to adequately evaluate light falling at angles ap-
proaching the horizontal. It has sometimes seemed to me that
this error has been responsible in the past for the tendency of il-
lumination tests to favor lighting units in which a large part of
the flux is delivered at steep angles.
Illumination tests made by amateurs are often of little value
because conditions are not made definite or are not properly re-
corded. For example, the observers may be careless as to
whether all the lamps in the installation are of the designated
rating, whether they are old or new, clean or dirty, or are oper-
ated at the correct voltage.
I quite agree that, on account of convenience and simplicity,
too much weight has been given to the intensity in a horizontal
reference plane. Often the intensity in some particular oblique
plane, or rather a number of such planes, is a more correct meas-
ure of the value of the illumination. To take care of such con-
ditions we have sometimes supplemented readings in the refer-
ence planes by a measurement of the illumination falling on par-
ticular surfaces where strong illumination is especially required.
In a way brightness measurements, which are becoming more
and more common, carry out the same idea, with the additional
value of including the effect of the surface.
The importance of illumination and brightness measurements
in connection with certain problems is so great that every effort
should be made to avoid any discrediting of such measurements
due to careless or imperfect work.
In measuring the beam candlepower of projected light — say,
from a parabolic reflector — it is important that the observing
stations should be far enough away from the reflector to insure
homogeneity of the beam. In this connection it is well to specify
use of portable; photometers 785
the distances at which measurements are made in giving the data.
Where practicable it is preferable to measure it at a distance cor-
responding approximately to the principal use of the light.
Norman Macbeth : It hardly seems possible that among all
the papers presented before this Society, that this is the first
paper on this most important subject. I know of no one better
qualified by experience than Mr. Little, and I only regret that
these results were not on record several years ago. I am not alto-
gether in agreement with Mr. Little on some of the points
brought up in discussions of this kind from time to time, and
particularly on what I feel is an over-capitalization of the il-
lumination measurements taken to secure the so-called utiliza-
tion efficiencies. That this consideration is uppermost is due very
largely to the general use in the past of the transmitting test-plate
and very largely also because in the investigations which Mr.
Little has been required to make these values were desired. I
have always felt that the largest field, by far, for the portable
photometer or illuminometer is in investigations of the bright-
ness of the various surfaces with which we have to deal in all
lighting installations.
The apparatus which he has perfected should be considered as
part of the regular equipment as it is all very valuable and neces-
sary. The manufacturers of photometers should include some
such devices with every instrument sold.
The telescope plum-bob and protractor illustrated in Fig. 8 is
especially interesting. A couple of years ago in the development
of an illuminometer I designed somewhat similar parts, but be-
fore the construction was completed we found that a clinometer
made by an English concern would do all we hoped for and cer-
tainly at a cost much less considering the greater number of clino-
meters made as compared with the more limited market for a
special instrument to be made for use with an illuminometer. This
instrument was a beautiful piece of work and required but a
slight addition to adapt it to our work. Furthermore, its cost —
twenty to twenty-five dollars — is considerably less than it could
be produced for in limited quantities.
Mention is made of a standardizing equipment. I believe that
a device for this purpose is most important ; and in my experience
786 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
I know of no other device as comforting and tending to save time
and generally facilitate illumination measurements and without
the incident worry as to whether the working standard lamp is
in an unknown condition.
This paper will be especially valuable in the Transactions. The
matter is of the greatest importance and has been covered in an
authoratative detailed manner which can only result in a better
understanding of this subject. Now that we have received full
sanction of that necessary brightness unit, the lambert, I hope to
see papers before this association having to do with illumination
measurements on the surfaces which are of the greatest im-
portance— those surfaces encountered by the eye in an interior —
and with data on their brightness range we will have more real
information as to what constitutes good illumination than is pos-
sible with our present data where only test-plate measurements
have been taken. The test-plate values help in working back-
wards to repeat a given result where all other conditions of
installation are similar. As this is an almost impossible combina-
tion, we should look forward to the day of more general recogni-
tion for illumination measurements of surfaces as they are in
daily use.
Mr. Little says that "It is obvious that illumination measure-
ments should be made in a plane, the illumination of which is the
principle purpose of the installation. This refers to height of
horizontal plane or to inclination of other planes which may be
studied. In some cases it may be desirable to determine the flux
density of the light incident on a surface inclined to the hori-
zontal. As in the case of the study of the illumination of school
desks, show windows, machinery, etc." I should like to ask, inas-
much as Mr. Little has stated the necessity of measurements
taken with the operator below the test-plate, if he would also con-
sider, that in all cases of school desks, etc. that the observer
should occupy the same position as a pupil at a desk or a man
working at machinery. We do not live in unfurnished rooms, and
most of the illumination measurements here described were in-
vestigations tending to bring out the utilization efficiency of
lamps, not the effectiveness of the lighting installation with
people in the rooms. It is particularly in measurements of
this kind that the body of the operator should occupy the same
USE OF PORTABLE PHOTOMETERS 787
position as an average occupant of a room or operator at a
machine.
Mr. P. S. Millar: The novice in photometry rarely, if ever,
considers himself capable of undertaking a photometric test util-
izing well designed set-up laboratory apparatus. It is one of the
unfortunate things about portable photometers that this same
novice approaches their use with all kinds of confidence in his
ability to make a photometric test and in the reliability of the
results which he obtains. Because the instrument is smaller and
less elaborate in appearance than laboratory apparatus, and be-
cause it is a simple matter to go through certain perfunctory
motions and to get an indication on a scale, there is a tendency to
assume that such process constitutes a photometric test. Those
of us who are familiar with the facts appreciate, as the author
has stated, that the requirements for care and the exercise of
common sense in the use of these instruments probably surpass
that which the ordinary practising photometrist is called upon to
exercise in routine work under established conditions.
This paper and discussion have made it evident that there are
two points of view regarding the use of portable photometers.
The author's viewpoint is that of one who is engaged in testing
work; his principal aim is to obtain accurate results from an
engineering survey, the report of which is rendered to a client.
He therefore avails himself of every practisable means of verify-
ing the test and the results. When practicable he prefers to as-
certain the total flux of light on some plane because the exper-
ienced photometrist or illuminating engineer can usually estimate
fairly well what the average intensity of light on a given plane
should be in any particular installation; and if the result is not
in accord with such estimate, the reason for the difference must
be ascertained. He makes it a point to obtain a measure of the
light produced by the illuminants as a part of his attempt to tie
together all the data of the installation into one consistent whole.
When a test of this kind is completed the photometrist feels
fairly certain that his results are reasonably correct, and this
certainty arises not only from his knowledge that he has exercised
care and intelligence in the conduct of the test but also from his
knowledge that the various data of the installation are in a
proper and consistent relation with one another.
788 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
This point of view by no means eliminates interest in and need
for measurements at arbitrarily selected points both of illumina-
tion intensity and brightness. It, however, requires that these
measurements be supplemented by the other measurements, which
ought not to be eliminated if a definite engineering report is to
be had on an installation.
The other point of view is that of a man who is doing illum-
ination work. With a minimum of bother and in the shortest
possible time he wants to know in general what the lighting con-
ditions are. He wants to know the high and low extremes of
intensity and brightness and gets a few values of the light here
and there where he is particularly concerned with the conditions.
The difficulty with such a survey is that the photometrist has no
adequate means of verifying his determinations and conclusions.
His results may be and often are quite erroneous, while there is
nothing to indicate that such is the case. In such a survey the
photometer may be wrongly calibrated, lamps which are pro-
viding the light may be operating at the wrong voltage and
various features of the installation may be improper. The
photometrist will not know the facts and his conclusions based
on his results may be unwarranted.
If we could only compel every man who uses a portable
photometer to go through the more extensive testing routine as
well as to make the occasional haphazard measurements at points
of special interest, photometric errors would be reduced and per-
haps eliminated, because that man would soon learn the real
fundamentals of photometric testing. It was not long ago that
we had occasion to use a photometer whose absorption screens
were erroneously calibrated by 10 to 20 per cent. Unless some
of the precautions advocated in this paper had been taken, we
would not have known that the instrument was erroneously cali-
brated.
Another reason favoring a systematic study of illumination in-
stallations is that only in that way can strict comparison be made
between different lamps, different lighting equipments, etc.
Where matters of commercial importance hinge on the results,
it is very important that photometric tests reveal the facts, and a
systematic study of the installation along the lines laid down in
this paper is essential to correct conclusions in such cases.
USE OF PORTABLE PHOTOMETERS 789
One speaker has suggested that the photometrist may be sub-
stituted for a workman in respect to the shadow cast upon the
work during a photometric test. In testing work it is a funda-
mental principle to separate as many variables as possible and to
examine each from the influence of the other. Shadows consti-
tute a very important variable and ought to be studied as shadows.
The distribution of light in a room and its intensity should be
measured, and then to determine the influence of shadows one
should study those shadows with respect to direction and density
under actual working conditions. It would be the simplest thing
in the world for a photometrist either to draw improper conclu-
sions regarding shadows while turning to arrive at the correct
ones, or to purposely create improper conditions if the shadows
were created by himself during the course of his testing.
Mr. A. H. Taylor: I would like to call attention to a few
things which we have found in practise at the Bureau of Stand-
ards to be very fertile sources of error. One of these is in setting
the voltage or current to its proper value. In practise it is best
to use a meter with which you have practically full scale de-
flection for the proper setting of the lamp in the photometer.
Some small meters, as you know, have no mirror backing, and
it is possible with these to make a very appreciable error due to
parallax. Another source of error is in estimating a fractional
scale division. Instead of trying to get the setting of the needle
to give the proper balance of photometer, it would be better to
set the needle on the nearest even scale division, making necessary
the application of a small correction factor to the results. This
factor could be incorporated in the calculations in the laboratory
after measurements have been made, and would eliminate this
source of error. A method which we have used with success, one
which does away with the necessity for application of a correction
factor to results, is the use of a temporary scale line. When the
photometer is standardized in the laboratory, and proper meter
setting has been determined, a piece of gummed paper, having
two fine ink lines ruled on opposite sides, so that one line is
directly opposite the other, is pasted on the glass of the meter. It
is so placed that the line on the paper, the needle, and the mir-
rored images of the needle and line on under side of paper are
790 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
in line. If the lines are ruled fine, meter adjustments can be made
quickly and very accurately, and difference between observers in
estimating fractional divisions are entirely eliminated. In using
this method, however, it is evidently necessary to be certain that
the meter casing is rigidly fastened so that there can be no rela-
tive movement between casing and scale. Additional ease of
setting may be obtained by the use of a reading glass fixed in
position over the scale.
In the initial standardisation of the photometer it is desirable
to make not less than ten to twenty photometer settings at the
determined voltage, since the average of that number may be
quite different from the average of only three or four readings.
The additional readings are so easily made that the increased
accuracy amply justifies the trouble.
In many portable photometers the field is far from uniform in
intensity. Some observers say that they balance the whole field,
and really do get very consistent results, even when the field is
not uniform. However, with the same photometer, observers
who confine their attention to a small portion of the field get
differences in their readings by making balances at different parts
of the field. Sometimes there is as much difference as 5 to 10
per cent, in settings taken at opposite sides of the photometer
field. The observer who is to read the photometer should have
this definitely in mind, and if he is reading only a small part of
the field, as is sometimes the case, that is the part of the field
which should be observed in standardizing the instrument.
Mr. W. F. Little (In reply) : Mr. Durgin has referred to
the caster truck for the photometer tripod. If a rigid tripod is
used the test-plate may be located over one of the legs at the be-
ginning of the test. Thus the photometer may be quickly and
accurately located over the test station without a plumb-bob and,
as the equipment is light, little time is lost in lifting it from station
to station.
A sufficient number of check readings will under ordinary con-
ditions prove sufficient to establish the representative values with-
out a duplication of apparatus.
Applying a factor to the scale reading instead of changing the
current on the photometer lamp to secure true values makes un-
USE OF PORTABLE PHOTOMETERS
791
necessary computation work. If the photometer is standardized
and found to read incorrectly, the characteristic curve of the
comparison lamp may be consulted and the current changed. A
second series of readings at the new current value will produce
a double check, and the calibration should be that much more
accurate.
Calibration for brightness is quite difficult outside of a well-
equipped photometric laboratory; therefore, it was not discussed
in detail in this paper. It is, however, done as follows :
Standardize the photometer in foot-candles using a reflecting test-
plate, then illuminate the test-plate (preferably from the rear to eliminate
stray light) to a definite intensity (probably 50 foot-candles) and measure
the illumination produced by it at a given distance (at least five times
the plate diameter distance). From the distance and the illumination,
compute brightness per unit area.
Once having standardized the photometer, a transmitting test-plate
may be used as a secondary standard by measuring the brightness of its
under surface with a known illumination produced on the outer surface.
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792 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Mr. Porter speaks of the necessity of accurately holding the
current of the photometer lamp. An examination of the char-
acteristic curve of the lamp will further emphasize this point.
The measuring instrument used for this purpose should have a
long mirrored scale, and a shunt such that the meter indication
is well toward the top of the scale. Long leads to the batteries
obviate the necessity of frequent changes in their location.
Mr. Anderson refers to the process of standardization of the
photometer. A quick and accurate method which has proved
very satisfactory is to use a standard lamp of sufficient candle-
power to produce 16 foot-candles on the transmitting test-plate
at a distance of at least two feet and with the use of rotating
sector disks the complete range of scale can be covered, includ-
ing the absorption glasses.
Mr. Taylor has spoken of errors caused by an insufficient
number of readings and inaccuracies in reading the electrical
instrument. These and many other errors (as mentioned in the
paper) creep into portable photometry. Experience alone will
suffice to place them in their order of importance, and the pho-
tometer operator should use judgment and discretion in the per-
formance of the work.
SPAULDING AND POTTER : GAS AND ELECTRIC COMPANIES 793
HOW CAN GAS AND ELECTRIC COMPANIES UNDER
ONE MANAGEMENT RENDER THE
BEST LIGHT SERVICE?*
BY A. B. SPAULDING AND N. H. POTTER.
Synopsis: This paper treats from the commercial standpoint only
the subject of service to the customer by gas and electric companies
under one management. It emphasizes the importance of service to the
customer, and outlines the question of service from a practical standpoint.
In discussing the selling force necessary for the proper handling of
lighting business, the authors recommend the employment of specialists
on gas illumination and specialists on electric illumination. The educa-
tion of the salesmen is considered and a successful local educational
course outlined. The education of the customer is discussed from the
standpoints of the manufacturer of appliances and the lighting company.
The relation between the representative and the customer is of special
importance and particular stress is laid on the matter of maintenance of
lighting units, which maintenance is in reality the "keynote of service."
One of the important subjects to-day among gas and electric
companies is "How can the best service be given ?" The engineer-
ing phases of this question have received marked attention, and
the improvement in design and operation of gas and electric
plants has increased the confidence of the public in the efficiency
of these plants.
This paper deals with the rendering of service after the product
is delivered, or beyond the meter. There are differences of
opinion as to how this can best be done.
Among the trio of products of gas and electric companies —
light, heat and power — light has always received the first place.
Upon the selling of this product depended the initial success of
all gas and electric companies ; and the early history of both in-
dustries is bound up inseparably with the development of their
lighting business.
There has been a radical change in the methods and personnel
of the selling force. Heretofore gas and electric energy were the
points of discussion with the consumer; but now illumination is
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
794 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
the topic. Instead of so many cubic feet of gas or watts of
energy, illumination is being sold.
On account of this advancement the illuminating engineer has
developed, and the Illuminating Engineering Society is an out-
come of the desire of gas and electric companies and manufac-
turers to render the public a service by united effort toward im-
proved illumination.
The present estimate of the work of any man must be, "How
much does he produce,"? and if any representative, no matter
what his printed title may be, does not produce, he is not efficient.
Selling and service should be synonymous, and service has
various phases. In order to render it intelligently it is essential,
first, that the representative be capable of laying out and super-
vising a lighting installation; second, that the consumer be edu-
cated to appreciate the difference between proper and improper
lighting, insofar as the value of proper lighting to his business is
concerned.
Service does not necessarily mean the reduction of bills ; it may
and often does result in an increase in the amount of business
with customers. Proper illumination is desired and must be the
primary factor in the discussion of cost, not only of electricity
and gas supplied, but of fixtures and first installation. Service,
therefore, means the providing of the illumination best suited
to each customer at minimum cost.
Both the representative of lighting companies and the public
must be educated to the value, use and maintenance of a lighting
installation.
GAS AND ELECTRIC SPECIALISTS ON THE SALE OF
ILLUMINATION.
The writers believe that with gas and electric companies under
one management specialists on gas illumination and specialists on
electric illumination are productive of the best results, particularly
as regards service to the customer. This method is in reality
intensive selling and each man becomes an expert in either gas or
electric illumination. Both men are selling the same thing, viz.,
illumination ; and unconsciously perhaps, each man picks out the
most likely prospects.
It would seem that there is no good reason for a gas or electric
company under one management adopting a policy which en-
SPAULDING AND POTTER: GAS AND ELECTRIC COMPANIES 795
courages only one source of supply. The duty of such a company
is not to pre-determine what source to sell, but to give the
customer the benefit of the best advice and leave to him the
decision.
That two sources are better than one is certain where gas and
electric units are installed for general illumination. The units
should harmonize with each other and with their sur-
roundings. The only question, which might influence the in-
stallation of a single source, would be its adaptability.
The argument has been advanced that by having one man sell
both gas and electric illumination, the selling force could be cut
in half. This is not true if the business is to be taken care of
properly.
It has been contended that the consumer is confused by having
two men advising different sources of supply. This may be true
where companies are under separate management and competition
dictates a policy of "Get business anyway, — but get it," rather
than a policy of real service to the consumer. With a company
under one management the consumer is not confused by having
information on both gas and electric illumination from different
men.
The customer should be credited with common sense and have
the privilege of choice. By having both sides advanced to him by
experts he is able to consider economy, convenience, safety, etc.,
and in the end be sure that he is getting that method of illumina-
tion best suited to his needs.
Summing up we find that separate gas and electric
lighting representatives are in the end no more expensive than
combination representatives. There is absolutely no question
that this separation does stimulate the trade in a healthy manner.
Each salesman becomes more proficient in the art of gas or elec-
tric illumination as the case may be. He has cooperative com-
petition and will necessarily have to watch his installations more
closely. He is also forced to make proper installations and to
render proper service after installation is made ; otherwise he is
likely to have "lost business" charged up against him, and he
keeps in closer touch with improvements in his particular line.
A man selling both gas and electricity is too prone to follow
the path of least resistance and to think, "If I don't sell gas, I will
13
796 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
sell electricity," with the result that a desire for better illumin-
ation is not created and therefore the best service is not given.
EDUCATION OF SALESMEN.
Lighting representatives should have good appearance, per-
sonality, and selling ability, together with a knowledge of the
principles of illumination. The salesman should make a general
survey of his territory and become familiar with its conditions.
He should make periodic tours after dark in the store section.
He can then pick out the improperly lighted stores and by one
night's work of this sort obtain sufficient leads to keep him busy
for several days. The writers know of several instances where
salesmen living out of town had never seen their territory illum-
inated. After making night inspections and following up leads
thus obtained, the volume of store business from their particular
sections showed a marked increase, and improved installations
also resulted.
The representative should visit other districts than his own
and, where possible, other cities and towns, thus acquainting him-
self with conditions, perhaps different than those in his territory,
which will enable him to handle more successfully new and similar
problems as they arise.
The lighting representative should, if he expects to become
more valuable to his company, do everything in his power to
increase his knowledge of illumination and other branches of the
business. This can be brought about by his becoming a member
of the Illuminating Engineering Society, National Electric Light
Association and National Commercial Gas Association, through
which he obtains at first hand, knowledge of all advancements in
the art of illumination as well as other subjects, particularly so
if he take advantage of the correspondence courses now offered
by the last two societies. If he be fortunate enough to have a
local section of any of these associations in his vicinity, he will
derive great benefits by attending all its meetings and taking an
active part in the discussions. In addition he will become ac-
quainted with other men in the same line, receive the benefits of
their personal knowledge and experience, and be able to recipro-
cate.
There are other means at hand of increasing one's knowledge
and keeping abreast of the times, viz., reading periodicals dealing
SPAULDING AND POTTER \ GAS AND ELECTRIC COMPANIES 797
with all branches of illumination and theadvertisingliteraturesent
out by manufacturers, which contains an education in itself. This
literature should be studied, not merely read ; for here is a fruit-
ful field of knowledge. Up-to-date data can be obtained by
having one's name placed on the mailing lists of manufacturers.
The sales manager in charge of these men should hold regular
meetings for the discussion of illuminating problems. Arrange-
ments should be made for visits to places like the testing labora-
tories and various fixture and lamp works. When some particu-
larly fine installation has been made in the vicinity, a party should
be made up to inspect and discuss it when it is lighted.
The company itself has a duty to perform in the education of
its representatives. It should encourage the men to study and
show that their efforts are appreciated.
The Public Service Gas Company and the Public Service Elec-
tric Company of New Jersey have given courses to develop the
desire for further knowledge on the part of the men.
The following course has been given by the Public Service
Electric Company.
( i ) "The Central Station Salesman ; His Duties, Troubles
and Needs."
(2) "Lamps; Their Manufacture and Characteristics."
(Lecture by representative of a lamp company,
and visit to factory.)
(3) "Light: Its Production; Its Properties. Some Laws
of Light."
(4) "Measurement of Light and Illumination." (Visit
to testing laboratories.)
(5) "Reflectors, Shades and Diffusing Globes; Their Use
and Abuse."
(6) "Direct and Semi-indirect Illumination."
(7) "Location of Units: General Consideration."
(8) "Residence Lighting."
(9) "Store Lighting."
(10) "Industrial Lighting."
(11) "Electrical Advertising."
(12) "Kw-h. Sales and New Business."
(13) "Wiring." (By a contractor.)
(14) "Review."
798 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
EDUCATION OF THE CUSTOMER.
The main object of a storekeeper for instance is to sell mer-
chandise; he has no desire to become an illuminating engineer;
but he is desirous of having his store and windows properly il-
luminated, provided of course, he is an up-to-date merchant. In
the event of his being behind the times — and there are many of
that kind — in fact, they are the ones who make up the best list of
prospects — he should be taught that a properly lighted store and
window are absolutely necessary for success in selling merchan-
dise.
The desire to have a properly lighted window, store, factory
or home lies dormant in every man, and under stimulus he wilL
unconsciously start a course of self -education by asking questions
and observing other installations and perhaps reading.
The company should send advertising literature acquainting
him with the proper method of using lighting units. For ob-
vious reasons this literature should be absolutely non-technical.
It should be attractive in appearance and so written that it will
hold the attention from cover to cover.
The manufacturer's representative should present the subject
of illumination first, and, secondly, the wares he is selling. The
architect, builder, electrician and gas fitter should be educated by
both the company and the manufacturer in order that they may
in turn do their part toward the education of the prospective
customer.
With these three different sources of information for the cus-
tomer properly co-ordinated, there would be little or no reason
for the absence of good lighting installations.
RELATION OF REPRESENTATIVE AND CUSTOMER.
As has been stated, the first consideration in this relation is the
impressing upon the consumer the value of proper illumination.
Poor installations have been made in every town and one of the
present difficulties is to have the customer realize the importance
of a good installation.
If the manufacturers of lamps and accessories were to deal en-
tirely through the gas and electric company whose sole idea is
proper illumination, or at least submit for the approval of these
companies the unit or accessory which is to be installed for a
customer, relations with the consumer would be much improved-
SPAULDING AND POTTER : GAS AND ELECTRIC COMPANIES 799
Cheap and inefficient gas and electric units have caused the
gas and electric companies much trouble. Such units are often
sold with an argument to the effect that the gas or electric com-
pany is robbing the consumer and will not sell such units because
they reduce the company's revenue. On account of such con-
flicting suggestions to the customer it has been found advisable to
demonstrate the correctness of recommendations made. The
Public Service Electric Company has been using for some time
very successfully window demonstration sets. These are made
up in portable form and consist of 4- ft. (1.23 m.) sections of pipe
with five outlets. Twenty-five, 40, or 60 watt lamps with proper
reflectors may be connected and in the case of large windows
several sets may be hung in line. The sets are hung by the repre-
sentatives in a few minutes by the use of screw eyes and
picture wire, and connections made by lamp cord to any available
lamp socket. As may be seen the outfit is very flexible and may
be made to fit almost any window condition. It may be advisable
to change these outfits to accommodate the gas-filled lamp on ac-
count of its better color value and increased efficiency.
The demonstration not only shows the display to better ad-
vantage, but the merchant gives more attention to the dressing of
his windows, which, combined with good lighting, results in in-
creased sales of his merchandise, thereby bringing the company
and customer closer together, the latter realizing that the com-
pany has rendered real service. By advising customers both as
to lighting and dressing of their windows, it has been possible to
have more light used not only for illumination, but as part of
merchandise displays. For instance, a customer who operates a
piano store desired a special dressing for his window and the dis-
play installed was a reproduction of a painting entitled "Just a
Song at Twilight." A reproduction of the original painting was
placed in the window and properly lighted. In one corner of
the window was a woman playing a baby grand piano and on the
other side a fireplace, in front of which the husband sat holding
a child in his arms. At one side of the room was a window
through which was projected light approximating moonlight.
From the fireplace was projected light of a ruddy hue. Alter-
nately the lighting of the window itself was flashed on, then the
effect as noted.
800 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Since the installation of this window the Public Service Electric
Company has been requested many times to dress other windows,
and in every case where this has been done, the number of ob-
servers of the window has been more than doubled, and in the
case of the window mentioned the observers were increasd 1,200
per cent, between 5 and 11 o'clock at night.
These installations, which are allowed to remain about a week,
usually convince customers of their value and lead to the in-
stallation of permanent outfits.
Factory lighting may be handled in the same way. Demon-
strations of either gas or electric lighting have been in many cases
the closing arguments for the sale of better lighting.
After the installation is laid out, it is necessary that the repre-
sentative should closely follow the development in the work to see
that the suggestions of the electrician or plumber are not such
as to spoil the desired results. It often occurs that the customer
accepting advice on changes in position of outlets and accessories
secures an incorrect installation and blames the representative for
whatever unsatisfactory result may ensue.
The representative's responsibility does not end with the demon-
stration. It is his duty to lay out the proper units, supervising
their installation and see that prompt service is rendered.
At this point the real service in lighting installations begins.
Once connected to the company's supply, service to the customer
never ends, and that all important question of maintenance begins.
In the case of electric lighting, maintenance is more or less a
matter of education. The customer should be taught first that
electric lamps have a useful life and that after a certain period it
is economy to throw away old and purchase new lamps. Sec-
ondly, reflectors decrease in efficiency with the accumulation of
dust, and like the plate glass window in the store must be cleaned
periodically.
The customer usually promises to attend to these details which
are in reality a part of his regular house cleaning, but the drop
in efficiency of the loss in illumination is by such small steps, that
it is never noticeable from day to day, and the customer being
intent on selling goods, gives little or no attention to the import-
ance of maintenance.
SPAULDING AND POTTER : GAS AND ELECTRIC COMPANIES 801
The lighting salesman may continue rendering service by calling
attention to any blackened lamps, dirty reflectors, etc. By stating
to the customer that this is his (the salesmen's) installation, that
he is proud of it, but that it cannot come up to his guarantee
unless properly cared for, the customer is usually awakened to
his responsibility in the matter and the habit of periodic inspection
and cleaning is formed.
In the case of a gas installation, maintenance is also a very
important matter. Thoughtlessness or carelessness is the reason
for depreciation in lighting value. Again the daily change or
drop in efficiency is so small as to be unnoticeable. Many cus-
tomers through not having time or not appreciating this drop in
efficiency continue using old or broken mantles with the result
that very poor service is obtained from the unit.
Gas companies have been trying for years to educate cus-
tomers to give proper attention to their lighting units, but in many
cases it is almost a hopeless task, with the result that in many
instances companies have launched maintenance departments to
do for the customer what he does not seem to care to do for him-
self. Probably the day is not far off when all gas companies will
have to maintain all customer's lighting installations in order to
insure proper illumination.
At this point the writers desire to mention a system of resi-
dence maintenance service by which customers receive periodic
inspections of all lighting units. This service includes cleaning of
glassware and adjustment of burners without any charge. The
men engaged in this work also carry samples of the latest types
of lamps and a full line of repair parts and accessories. If new
material is sold to replace that which is broken, no charge is made
other than the regular selling price of such material. By this plan
the company is enabled to attend to all complaints received before
3 p. m. the same day. This plan is being tried out by the Public
Service Gas Company in one city in New Jersey with such good
results that in a very short time it is expected that the sale of re-
pair parts and additional units will alone make this department
self sustaining, not to mention the increased satisfaction on the
part of the consumer nor the added consumption derived by hav-
ing more units in good working order. This department is
productive of many sales and materially strengthens the selling
802 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
organization of the company. The aforementioned plan is similar
to the so-called Toronto Plan with which many of you are no
doubt familiar.
It is the opinion of the writers that in order that a gas and
electric company under one management may give the best light-
ing service, separate representatives who are specialists in the
application of each lighting source should be employed. These
representatives should be encouraged to keep in touch with the
science of illuminating engineering and the most advanced thought
in modern salesmanship. The company should lead the customer
to an intelligent appreciation of proper illumination and by the
adoption of a maintenance service should make him feel that the
company is genuinely interested in his continued satisfaction.
DISCUSSION.
Mr. Preston S. Millar: I think the work of electric and gas
supply companies, their engineering and operation up to the
meter, is likely to be much better standardized in the several com-
munities than are the conditions in the consumers' premises be-
yond the meter ; all sorts of policies obtain among such compan-
ies in regard to the treatment of the consumer in his own in-
stallation. The service, whether gas or electricity, is translated
into illumination by lamps and fixtures.
Gas lamps are in general not what they ought to be in residence
lighting. Open flame burners are still used very largely and the
possibilities of gas for illuminating purposes are not being real-
ized.
I have recently had the privilege of conducting a survey to
obtain what condition the electric lamps are in when they are
offered to central station customers. A great many tungsten
filament lamps are distinctly inferior to the standard. The con-
dition of some lamps that are offered to the consumer by repu-
table dealers and contractors, and by other selling agencies rang-
ing down to the five and ten cent store, is such as ought to com-
mand the attention of every central station. Unless care is taken
by the central station as to the quality of lamps that are sold to
their consumers, electric lighting is likely to get into some of the
difficulties that gas lighting is laboring under.
GAS AND ELECTRIC COMPANIES 803
In the matter of fixtures I have often wondered if gas and
electric supply companies could not do a great deal in the way of
cultivating good public opinion, pleasing the customer and pro-
moting the sale of gas and electricity by making pleasing fixtures
available on attractive terms. I think that men should be em-
ployed to select and design artistic fixtures which will give pleas-
ing effects, fixtures that will bring out the decorations of the
room to the best advantage, diffuse and tint the light so that it
will be pleasing to the eye and comfortable. In so doing there
may be an increase in the customer's bill, but this will not be
objectionable to the customer if the lighting pleases him. The
experience I have had indicates that once the lighting is im-
proved in a house in the manner I have indicated, the customer
is willing to pay a larger monthly bill because he has more pleas-
ing lighting and he would not go back to the lower bill and the
inferior lighting for anything. I know of very little that is
being done in the way of cultivating in this way the opportunities
which are offered.
Finally I want to compliment the authors of the paper ; it seems
to me that it is just the kind of a paper that the Illuminating
Engineering Society wants to see brought to the attention of the
gas and electric supply companies throughout the country and I
would like to recommend that the paper be printed for general
distribution among gas and electric companies ; I think it would
do a great deal of good.
Mr. R. B. Ely: I believe the lighting companies are more
inclined to the belief of selling a service rather than gas or
wattage and with that in view they are trying to furnish all, that
their advertising departments are talking about, such as proper
illumination and upkeep of system to obtain the maximum re-
sults at a minimum cost. I would like to inquire as to how far
the Public Service Company has gone in checking up the recom-
mendations of their representatives, whether they follow the
recommendations up with any tests, and to what extent they are
going in the matter of demonstration, the demonstration of fix-
tures for the interior of stores, both gas and electric, and the
period of time of such demonstrations. I would also like to in-
quire whether the men on this particular end of the work, the
804 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
lighting service work look after the commercial conditions, such
as contracts, to see that their consumers are receiving the best
possible rate and whether the small repairs that may be necessary
are noted and taken care of by this department.
Mr. H. T. Owens : The illuminating engineers of the United
States are the fixture salesmen ; they have more to do with light-
ing than all the rest of the illuminating people put together. The
salesmen in retail fixture stores never come to the meetings of the
Society and they don't use the title, but they have more to do with
lighting than the members of this Society. The paper by Mr.
Spaulding and Mr. Potter tells how things could be done and not
how they are done. I know of no company that has two illumin-
ating engineers. In the eastern part of this country there is more
good gas than electric lighting for the reason that the gas com-
panies handle fixtures and sell them and the type of fixture they
sell on the average furnishes better lighting than the kind of fix-
ture that the small electrical contractor sells.
Mr. W. R. Moulton : In Baltimore it has been found advis-
able for the central station to not only give advice regarding il-
lumination, but also sell and install the proper fixtures at a fair
price to the consumer. By so doing it is possible to actually give
better service to customers and at the same time increase the in-
come. I do not believe there is another large central station work-
ing on this basis.
Referring to the paragraph where the authors suggest that the
salesman handling a prospect be allowed to lay out the entire in-
stallation. This is no doubt advisable for simple installations, but
when the problem is completed it should be referred to the de-
partment head, or someone else who is capable of giving special
advice.
It is true one can often increase the energy consumption
of a customer's installation and at the same time have that cus-
tomer pleased. For example, he may be spending $6.00 a month
for electricity or gas, and may be receiving poor illumination,
poor service, poor return for his money. With proper equipment
installed to give him the correct result, his energy bill or gas bill
may increase to $10.00 per month, but if at the same time the ser-
vice and lighting is thoroughly satisfactory, the customer will not
object to the increase in operating cost.
GAS AND ELECTRIC COMPANIES 805
It would certainly be inadvisable to leave the selection of the il-
luminant to the customer, as in few cases would he be capable of
selecting what is most suitable to his conditions. By studying his
present conditions and service and being familiar with results
possible with the different methods of lighting, one can definitely
recommend a form of lighting that would be best for the cus-
tomer's special case. The gas salesmen and the electric salesmen
should not be allowed to compete for his business, as they are
only liable to confuse him as to the best method of lighting his
establishment.
It would be well for lighting salesmen to study the results of
different types of installations at night. There is a broad educa-
tion to be obtained by studying and analyzing different lighting
installations, both as to a judgment of the present results and a
possible change that would result in improved lighting conditions,
necessitating only a slight expenditure in revising the installation.
As the central station and its representatives give recommenda-
tions for lighting, why should they not also follow these with the
actual sale and installation of the necessary equipment. They can
then be absolutely certain that the result will be satisfactory and
forestall the possibility of unsatisfactory results that often come
about when the instructions are turned over to some other con-
cern to carry out. Such a method of handling business keeps the
entire responsibility just exactly where it belongs, namely with
the central station, who has not only recommended, but installed
the equipment to give best results.
Chairman, C. A. LittlEField: A great deal has been said
this morning about education. A special man or a man holding a
managerial position is highly developed, not alone in his particu-
lar field, but in the general line of his business. But it is not so
much of him I wish to speak as of the man who is out on the
street — the average salesman. It is not an over-easy matter to
get a good salesmen; some people are naturally salesmen, they
are born — not made. But it is sometimes possible to improve
even this man by giving him a broader educational foundation
upon which he may base his selling problems. Some people can
sell anything from a domino to a dynamo. But as we study this
paper by Messrs. Spaulding and Potter, we cannot help but be
impressed with the fact that even these successful salesmen have
806 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
something to learn. I presume there is not a manager of a single
corporation — large or small — who is not constantly striving to
improve the calibre of his men, and it is this fact that is causing
such a widespread interest in the general subject of the education
of salesmen. We see this in the National Commercial Gas As-
sociation, the National Electric Light Association, and other as-
sociations of larger and smaller sizes that are conducting courses
of education. It is really astonishing to see the results that are
being achieved by these several organizations and the eager re-
sponses that are being made to the advertised courses, not only
by the companies for their men, but by the men themselves, who
are paying for these courses out of their own pockets, with the
sole object of making themselves better and broader men. Men
themselves are beginning to realize that their positions are much
more secure the higher they are developed, and in the proportion
as they themselves strive to improve their mental capacities do
they improve their position as employees of successful corpora-
tions. I think that altogether too little has been said on this most
important subject. Speaking personally, I am very glad indeed
that this paper has been brought before this convention. I should
like you to think this over seriously, and if you are in a man-
agerial position yourself to put into effect the many recommenda-
tions of this excellent paper. But whether your position is that
of a manager or otherwise, I trust that you will bring it to the at-
tention of the executives of your company on your return home.
Is there any further discussion?
Mr. Z. M. Hyer: I think a salesman can do better work
if he has ony one commodity to sell. For myself I doubt if I
could go out and conscientiously recommend gas, having sold
electricity for a number of years. I could not do this unless I
were employed by a gas company that was not handling electric
products and I feel that the gas salesman would be in the same
position : he could not conscientiously talk up electricity after
having sold gas. It is natural that a man would feel a certain
loyalty, have a certain feeling about the commodity that he is
selling; he has to have confidence in it, and faith in it, and if
he has that I do not see how he could offer another form of
illumination as a substitute. I think both illuminants have their
special uses, but for illuminating purposes I think electricity has
GAS AND ELECTRIC COMPANIES 807
many advantages over gas and I don't feel that I could go out
and recommend gas to a customer for all purposes ; I could not
go out and be unbiased in my judgment.
Mr. Norman Macbeth : The paper is valuable in calling at-
tention to a serious situation existing in many territories served
by combination companies. The lack of reasonably aggressive
sales methods and the policy of waiting, often results in letting in
the gasoline isolated plant. At the bottom of the second page
there is the following statement : "It would seem that there is no
good reason for a gas or electric company under one management
adopting a policy which encourages only one source of supply.
The duty of such a company is not to predetermine what service
to sell, but to give the customer the benefit of the best advice
and leave to him the decision." It is true that there are a great
many factors entering into an installation with which the cus-
tomer is more familiar than the representative of a utility com-
pany. Given the right information about rates, costs and load
factor conditions he quickly decides whether he will have gas
or electric service ; there is very little opportunity for argument,
provided, of course, that the information given the customer is
as unbiased as it should be.
Toward the end of the paper it is stated, "It is the opinion
of the writers that in order that a gas and electric company
under one management may give the best lighting service, sep-
arate representatives who are specialists in the application of
each lighting source should be employed." It has never appeared
to me that it is necessary to have separate representatives. The
extent of the information sought by the consumer is not
difficult to secure, nor should it be involved as to require
separate specialists. The average commercial installation to a
specialist presents nothing difficult ; the possibilities of the avail-
able gas and electric sources have been so thoroughly studied and
their limitations are so well known that many of the installations
required are simple problems. A plain presentation of the facts
regarding the gas or electric service available for a particular
purpose is sufficient to enable the consumer to reach a decision.
There is just one more question. How are the men paid ;
are they given a regular salary or do they work on a commission
8o8 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
basis ; and also how many hours a day do they work ? I have
known cases where men have worked on a commission basis
where they could not limit their work to the ordinary nine to
five day. Their interest in the work and the necessity of seeing
their customers at night required that they work until ten o'clock
at night. How do you arrange the day's period and compen-
sation ? What are your working hours ?
Mr. T. J. LiTLE, Jr. : Relative to the sale of both gas and elec-
tric units by combination companies, I would like to say that there
are certain corporations in this country, such as large department
stores, which are coming to believe that for their own protection
no one system of illumination should be entirely depended on.
They believe that for continuous illumination in their store it
is advisable to have both forms of lighting. Now I am not
speaking in a general way; I have in mind several instances
where these great corporations operate both systems continu-
ously, not just for an emergency to be used in case of accident,
but as a continuous system, operated simultaneously. Now the
combination company in serving a community has an advantage
that the separate company does not have, and it seems to me
that broad minded empolyees of such a company should bear
that in mind. I understand and feel myself that the illuminating
engineer is either in favor of electric or gas illumination, but
if he is connected with a combination company he should sell
both products and I don't think there should be a single large
department store in this country, nor any large building, in which
a great number of people assemble, in which the single system
should be installed ; some auxiliary system should be provided
and this should provide continuous illumination. Take, for in-
stance, the basements in the large department stores. If any-
thing happens to the lighting system, a general panic is likely
to occur and there will be a scramble for the exits and accidents
are sure to happen ; and I think that these stores should provide
an auxiliary system just to meet such emergencies. There are
local ordinances that provide for this in armories and other
large buildings where a number of people are gathered and I
think the lighting companies themselves should provide for the
use of some auxiliary system.
GAS AND ELECTRIC COMPANIES 809
Mr. Z. M. HyEr: I might give a little information that would
be of interest, relative to the dual lighting in New York City.
We have done away with dual lighting in large buildings to a
large extent. This is due to the fact that the city authorities
compelled the electric lighting companies to put in two distinct
services. Our company has developed an apparatus, an auto-
matic switch, by which it is possible to switch the current from
one service to the other automatically. If the service goes off
on one circuit the switch operates which immediately cuts in the
other circuit. We are the only company that I know of that
use a switch of this kind. I had an experience only a short time
ago: the electrical contractors of New York City has an outing
on Staten Island and were going to have a vaudeville entertain-
ment in the evening. We assembled in the hall and when the
first number was put on the electric lights all went out; in fact
they went out all over that section of the island. They had a
dual system of lighting installed in the building and the porter
came along with a step ladder and matches to light the gas
lamps. The first fixture he went to had four jets on it and
after about 15 minutes he succeeded in getting one of them
lighted ; the delay was due to the fact that he had to renew all the
mantles. We were an hour waiting for him to get all the gas
fixtures in proper shape and by the time he did the electric lamps
were in operation again, so the gas was not needed.
Mr. L. C. Porter : I would like to bring out the point that gas
when used as an emergency system usually consists of a few
open flame jets without any means of lighting them, unless some-
body goes down in his pocket and gets a match ; and then possibly
the key to the fixture can not be found, which is as bad as if there
were no fixture there. I do not call that a dual system at all.
The dual system that is built along lines as nearly identical as
possible and both controlled by the same switchboard is the only
kind of a system to install. The point was brought up about
glassware being developed for gas lighting that will give the same
appearance as the electric lighted glassware. I think the manu-
facturers of mantles can get the desired color in a measure by
using an amber light mantle and also I think the electric man
should do his part ; he should use a lamp with a very white light,
possibly a gas filled tungsten lamp, and I think it could be worked
8lO TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
and developed so that one could not detect the difference between
the sources either when lighted or unlighted.
Mr. T. J. Litle, Jr. : I would like to say one more word.
Some people argue that there is no necessity for a dual system as
they have never had occasion to use it, but you might as well say
that there is no necessity to have fire escapes on a certain build-
ing because you have never had a fire there. I think a dual
system is absolutely necessary in halls and buildings where a
large number of people are apt to congregate. Some of the
larger corporations have insisted that the illuminating company
themselves do this work and I know of several cases where an
illuminating company, supplying only one system, was compelled
even though they had to buy the gas, to put in the dual system.
In a combination company, of course, this would not be necessary.
Mr. G. B. Nichols: In reference to the question of dual
lighting systems, I believe that this is somewhat a question of
locality, depending on the class of service furnished. In first-
class cities generally, where the service is of such a nature that
interruptions are very seldom, if any, and particularly those
cities where all of the wires are underground and where on large
installations dual systems of electric feeders are extended into
the building, it appears unnecessary for two classes of service.
In cities, however, where the electric service is maintained by
overhead lines and particularly those fed from water power
plants at a considerable distance, a dual system undoubtedly
would be of some advantage.
Mr. F. A. Vaughn : I can see where the independent con-
sulting engineer has considerable advantage over some of you. I
think he can look at the problem without any bias from either
side. The remarks of a previous speaker remind me of a system
which has been installed in two department stores in Milwaukee
where it was felt decidedly necessary to have an emergency gas
installation. Instead of having the additional gas units out of
symmetry, the gas unit was made as nearly identical as possible
with the electric unit; its apearance was almost identical, even to
the extent of carrying out the chain effect. A rigid hollow chain
was made, which would allow the gas to flow to the mantle. To
the customer, the store appeared to be lighted by electricity — by
GAS AND ELECTRIC COMPANIES 8ll
only one form of illumination — and in case of accident to either
system there would be sufficient light available to illuminate the
counters. This installation was not only to guard against acci-
dent in case of panic, but also against theft, which is a large
factor at such a time. The details were carried out a little further
by providing push buttons for lighting the gas ; these were on the
same gang as the electric push buttons and the clerks did not
know which unit they were turning on, gas or electric. This
made a complete continuous auxiliary system as an emergency
equipment. The ordinary emergency equipment is sometimes
difficult to get on in time to prevent a panic.
Mr. N. H. Potter : Mr. Macbeth mentioned the combination
man versus the special man selling both kinds of energy. He
brought out the only strong argument in favor of one man selling
both kinds of energy, namely, gas and electricity. Naturally there
is a difference of opinion regarding which is the best plan to
adopt, but as stated in the paper, we think that special men are
better than the combination man. A combination man is too
prone to follow the lines of least resistance; he naturally thinks
that he will get the installation for either gas or electricity ; hence
he may not advise the best installation.
Regarding the number of men employed by our company, there
are four specialists on gas, and eight on electric lighting, besides
fourteen solicitors who sell gas lighting units throughout resi-
dential and business sections. These men are educated to such
an extent that they are competent to properly advise a customer
as to the best installation for his particular requirements.
Strictly speaking, they are not technical, but practical men, and
they are forced to meet conditions as they find them.
In a majority of cases their work consists principally of trying
to correct mistakes that were made in the layout of the original
installation, regarding location of outlets, etc. They come in
contact with many conditions of this character. If a customer
has insufficient or improperly placed outlets in a store, the only
thing to do is to extend the line, place an additional outlet or
change the location of the existing outlets and then install the
best fixture for his particular requirement.
Mr. Ely spoke of the men in the house lighting maintenance
14
8l2 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
department. I think this is a more important proposition in a
gas company than in the electric company. We furnish the
repairs and the lamps in good condition free, but charge for the
material used in putting the lamp in perfect condition. This,
however, is a new department and is in an experimental stage, but
promises to be a very good addition to our present organization.
Mr. Owens touched on the gas company advising a good type
of fixture, and installing them. I take it that he means the com-
pany would install the fixtures. We have tried to place some
semi-indirect lighting in homes and stores, but the main disad-
vantage we have to contend with is that the customer is inclined
to look at the unit itself, thereby considering the intensity of
the source instead of noting the effect and the utilization of
the light to a better advantage. This is due to a lack of edu-
cation on the part of the general public, a condition which will
take some time to entirely overcome, and accounts for the higher
intensity units meeting favor.
Mr. Moulton said that the representative should consult the
department head, that he should not be allowed to lay out the
installation, and that he should consult the engineer. This is
done in our company if the salesman is at all in doubt. The
sales manager also instructs the man regarding just what are
considered good installations for different cases and how to install
them. Of course the longer a man is with the company the more
proficient he becomes, but we cannot always have men with ex-
perience filling these positions. It is therefore necessary to
employ from time to time new men, who are instructed as soon
as possible. It is better that men should be competent to handle
the average case instead of bringing every installation to the
attention of the department head.
If the manufacturers of glassware would adopt some measures
by which they could make a bowl which when illuminated by gas
would give the same color as a bowl illuminated by elec-
tricity, such a scheme would be a great improvement toward
perfecting the appearance of dual installations. At present there
is a noticeable difference in the color of the glassware when
lighted by these two agents. The glassware lighted by gas retains
nearly the same color when lighted as when extinguished, while
electric light imparts an orange or pink tint to the glassware.
GAS AND ELECTRIC COMPANIES 813
The elimination of this condition can only be accomplished by
development of glassware by manufacturers of glassware.
Manufacturers of fixtures do not appear to give enough attention
to the design and construction of good combination fixtures.
All the electric solicitors are on a salary. The gas solicitors
are on a salary with an addition of a bonus system. Our solicitors
work from 8 a. m. until 5 p. m. unless the men wish to work
after hours in order to inspect lighting conditions after dark, or
keep appointments after hours. All solicitors do this more or
less, especially those who have a desire to get all the business
possible.
814 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
LIFE TESTING OF INCANDESCENT LAMPS AT THE
BUREAU OF STANDARDS.*
BY G. W. MIDDLEKAUEE, B. MULLIGAN AND J. E. SKOGLAND.
Synopsis: The method employed by the Bureau of Standards in the
inspection and life testing of incandescent lamps for the federal govern-
ment is outlined and a description of the power plant, the life racks, and
the photometer is given. Particular attention is directed to the special
equipment of the photometer. This includes a watts-per-candle computer
and a recording device by which observed values of candlepower, watts,
watts per candle, and actual life are recorded on a separate card for each
lamp. These records are made in such a way that life at forced efficiency
is corrected to life at normal without computation or reference to tables
of factors. The procedure in actual measurement and testing is described
with considerable detail.
CONTENTS.
Introduction 816
Purposes of a Life Test 817
1. General 818
2. Special Purposes of Bureau of Standards Tests 819
Selection of Life Test Lamps 820
Measurement of Life Test Lamps 821
1. The Life Test Photometer 821
a. General Construction 821
b. Instruments and Candlepower Scales 822
c. Wiring and Special Resistances 823
d. The Watts-per-candle Computer. 824
e. The Recording Device 825
f. Features of the Record 827
a. Detection and Compensation of Errors 827
p. Increased Accuracy in Life Values 828
2. Methods of Measuring and Recording Observed Values 829
a. Rating of Lamps for Life Test 829
b. Details of a Photometric Run 829
The Life Test 832
1 . Design of the Installation 832
a. Wiring and Voltage Adjustment 833
b. Voltage Regulation 834
c. Current Generator and Voltage Transformers • . • 835
d. The Life Test Racks 835
e. Measurement of Lite Test Periods 836
2. Records Taken During Life Test 836
Summaries of Life Values 836
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
MIDDLEKAUFF, MULLIGAN, SK0GLAND: TESTING OF LAMPS 815
INTRODUCTION.
The first edition of "Standard Specifications for the Purchase
of Incandescent Electric Lamps,"1 issued in 1907, was the result
of concerted action on the part of the federal government de-
partments, representative lamp manufacturers, the Electrical
Testing Laboratories, and the Bureau of Standards. The pur-
pose of these specifications was to establish such standard methods
of initial inspection and life testing as would permit their adoption
by the government and make them available to the general public ;
so that all purchasers of incandescent lamps, by including these
specifications in contracts, might realize the benefits of their use.
Application of these specifications necessitates careful initial
inspection and reliable life tests. The specified life test procedure
is so exacting and the quantity of lamps to be tested on any con-
siderable contract so large that the purchaser, unless his facili-
ties for testing are complete, must of necessity refer, at least, the
life test work to some reputable testing laboratory. It was, there-
fore, the natural outcome that the Bureau of Standards should
be sought and recognized by departments of the government as
the authority on life tests. Initial inspection is so closely related
to life test procedure and its efficiency so pronounced in the ef-
fect on the results of life test that the Bureau, almost of necessity,
undertook this part of the work as well.
The design of a life test installation was therefore begun early
in 1908. This was developed by Messrs. E. P. Hyde, F. E. Cady,
C. F. Sponsler, and H. B. Brooks, under the direction of Dr.
E. B. Rosa, chief of the Electrical Division which included the
photometric section. A lamp inspector was appointed in July and
the plant was put into operation in October of the same year
(1908). About this time Dr. Hyde and Mr. Cady left the service
of the Bureau and the work has since been carried on and de-
veloped mainly by the authors of the present paper, under the
direction of the chief of the electrical division.
The whole life test equipment was originally installed in the
mechanical building which houses the power plant of the Bureau.
In 191 3 the life racks, transformers, and photometric apparatus
were removed to two adjoining rooms on the third floor of the
1 These specifications are issued by the Bureau of Standards as Circular No. 13, which
has been revised from time to time and is now in the seventh edition.
8l6 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
new electrical building which was then nearing completion. Al-
though some parts of the equipment are differently arranged in
the new building, the general plan has remained the same as orig-
inally designed.
The introduction of new classes of lamps, however, rendered it
advisable to make considerable changes in the original photo-
metric equipment and in the details of the method of testing.
These changes have been made from time to time by those who
have been most intimately associated with the work. The equip-
ment as it now stands and the present method of the Bureau's
life testing procedure in all its details are, therefore, the result of
a gradual development in which various persons have been of
assistance.
From the beginning the magnitude of the work of inspection
and life testing has been constantly increasing year by year in
consequence of the natural growth of the government's pur-
chases of incandescent lamps. Fortunately, however, the quality
of the lamps supplied has, in most cases, been fairly uniform and
also above the requirements of the specifications, so that full and
reliable data on the lamps supplied by each manufacturer have
been obtained by submitting to life test a yearly total of not over
five thousand lamps which represent about one and a quarter mil-
lions of inspected lamps.
Since inspections and tests are made primarily for departments
of the government, outside tests are accepted only "when special
circumstances make the test of more than usual importance." A
specified fee is charged for work of this kind.2
In the following description of apparatus and methods of life
test, an attempt is made to indicate the essential features of this
work and the manner in which the testing is at present actually
conducted.
PURPOSES OF A LIFE TEST.
General. — A life test may be run for any one of several rea-
sons. For example, a manufacturer who desires quick results in
order to test the effect of some modified construction or change
in material may choose to burn the lamps selected at a voltage
2 Fees for Electric, Magnetic, and Photometric Testing; Bureau of Standards Circular
No. 6, p. 26, 1914.
MIDDLEKAUFF, MULLIGAN, SKOGLAND : TESTING OF LAMPS 817
greatly in excess of that employed in normal operation thus caus-
ing the lamps to fail in a few hours. Unwarranted confidence is
sometimes placed in tests of this kind for other purposes, and
attempts are made to evaluate life at normal voltage from the test
results, whereas no known constants for these life corrections
will apply in all cases. Although relative results may be of some
value, they often point to conclusions not at all in agreement with
those which might be drawn from a test at a voltage correspond-
ing more nearly to rated efficiency.
Comparative tests of greater value may be run at or near
normal operating efficiency, even on a line of uncertain voltage
regulation, by placing both tests side by side on the same circuit.
However, the voltage applied to the lamps of each test must be
such that the average efficiency of the two groups is the same, or,
if differently rated and burned at one voltage, correction factors
must be applied to reduce the test results of one group to their
equivalent life at the efficiency of the other group. In all cases
the initial (test) efficiency must be known, if test results are to
be correctly interpreted. It should be emphasized that relative
results only are obtained by such a test, unless the voltage regu-
lation is that indicated in the specifications under which the lamps
are tested.
In contradistinction to these rough tests are those in which
actual values of life at normal efficiency are obtained for any
group of lamps. This necessitates great care in initial rating and
constancy of voltage at which the lamps are operated on the life
test. By choosing test efficiencies within a range through which
factors for life correction have been fully established, the time
necessary to complete the tests may be materially shortened.
Life tests at the Bureau of Standards are of this kind.
2. Special Purposes of Bureau of Standards Tests. — Although
the chief concern of departments of the government in connec-
tion with tests under Standard Specifications is to secure reason-
ably prompt delivery of lamps which meet the specified require-
ments, a consideration almost equal in importance is the determin-
ation from the life tests of the relative standing of the various
manufactures as regards quality of output. The relative quality
8l8 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
thus determined is referred to and given due weight in deciding
upon future awards of contract.
The evaluation of a lamp life to as high a degree of accuracy
as is possible in testing a large quantity of lamps has no doubt
guided the manufacturers to some extent in their improvements
of efficiency ratings, notably in the tungsten lamp. Consequently
manufacturers and purchasers receive all available service and
assistance not only from the actual test results but from con-
clusions drawn therefrom.
SELECTION OF LIFE TEST LAMPS.
The Standard Specifications, in accordance with which all
Bureau tests of lamps for the government are made, recognize the
importance of a proper selection of samples for life test. It is
assumed that no lamp can accurately represent the life of a group
unless it accurately represents the group in other respects. Hence
great care is exercised in the selection of the samples for life
test, and no sample is taken unless the lamps have first passed
the prescribed initial tests.
These initial tests are made by Bureau inspectors3 at the factory
of the manufacturer, and regular factory apparatus is used. Such
testing equipment as is required in the work of inspection is usually
assembled in an inspection department, so that factory work is not
interfered with. In the larger factories, where initial tests under
specifications are made for a number of purchasers, certain opera-
tors are employed most or all of the time in the inspection de-
partment. It is their duty to render the inspectors such assistance
as may be required in making initial tests. Besides one or more
photometers this department contains vacuum test equipment,
special sockets supplied with current for lighting up the test lamps,
and, in factories manufacturing tungsten lamps, racks for sea-
soning or "aging" the lamps selected. This last-named equip-
ment has been introduced as required by Standard Specifications,
because of the new process of exhaust, which produces a ductile
filament, not, however, stable in its electrical characteristics ; so
that a certain amount of burning is necessary before the current
and candlepower reach values sufficiently steady for accurate
measurement.
3 One inspector is employed continuously and another is sent out to assist him when
necessary.
MIDDLEKAUFF, MULLIGAN, SKOGLAND : TESTING OF LAMPS 819
The quantity of lamps selected for initial tests is specified
as 5 per cent, of the total of a lot including only lamps of the
same size, class, and voltage range, and not less than ten lamps
from any one lot. The number of lamps to be included in a lot is
left to the judgment of the inspector.
The lamps must conform to certain specified requirements as
regards bulbs, bases, filaments, and vacuum. Lamps which pass
these requirements are then run on the photometer, and in de-
termining their acceptability, tables of allowable limits of watts
and candlepower or of watts per candle, as given in the specifica-
tions, are applied. In calibrating the photometer for these tests
the inspector uses standards which have been certified by the
Bureau for candlepower and current. A lot of lamps is accepted
if the number of defective lamps on either test is below the speci-
fied percentage of the total.
The next step is to compute from the records of the photom-
etric test the mean values of individual groups of test lamps
representing not more than 250 lamps from any one lot. The
lamp nearest the mean value of each group is selected, labeled,
and sent to the Bureau to represent the group on life test.
MEASUREMENT OF LIFE TEST LAMPS.
In order to facilitate the photometric measurement of the life
test lamps and still secure a permanent, accurate, and as nearly
as possible, automatic card record of each lamp tested, certain
modifications and additions have been made to the photometer
used in this work. As these features are decidely special and not
found elsewhere, their construction and use are fully explained
in what follows, not only that the method of measurement de-
scribed later may be better understood but also that the equip-
ment may be duplicated by anyone desiring to use it.
1. The Life Test Photometer. — (a) General Construction. —
The general construction of the life test photometer is shown in
Fig. 1. A Lummer-Brodhun contrast photometer head is mounted
upon a movable carriage between the test lamp and comparison
source, the distance between the last two mentioned being
250 cm. The comparison lamp, a 100-watt tungsten, is placed
in a mirror-backed box fronted by a ground glass window. This
window presents an approximately uniformly illuminated surface
820 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
to the photometer, so that the glass plate acts as the effective light
source and is so considered. The mirrors within the box are
employed to increase the illumination of the window to a practical
working value, the effective area of the window being adjusted by
means of a variable diaphragm or shutter,4 this adjustment
being used in calibrating the photometer. By the screening sys-
tem used, stray light is so effectively excluded from the photom-
eter screen that measurements are made in a curtained booth about
8 feet high under conditions which might be denned as approxi-
mately "semi-daylight."
The standard lamp socket may be rotated in a direction depend-
ing upon the position of a knee switch which reverses the current
in the armature of the motor; so that lamps may be rapidly turned
in or out of the socket and may be rotated during measurements.
Current and voltage leads are joined to the lamp rotator by
means of mercury cup connectors. Storage battery current is
used in all measurements and available line voltage is adjusted
by means of end-cell switches.
(b) Instruments and Candlepower Scales. — Current through
the standard or test lamp is read on a millivoltmeter connected
across a separate shunt. Standard or test lamp voltage is read
on a Brooks deflection potentiometer.5 On this instrument the
balanced portion of the e. m. f . is read from the dial which is
arranged in steps of two volts. The unbalanced portion produces
current in the galvanometer circuit with consequent motion of a
pointer over a scale calibrated in o.i volt divisions through a
range of 1.5 volts above and below the dial setting; so that 0.01
to 0.02 volt is the smallest readable deflection, and the pre-
cision of any setting is within these limits. In practise a null
method is used and voltages corresponding to dial settings are
chosen in the measurement of all test lamps. Certain modifica-
tions described later have been made in the connections of this
instrument to facilitate the convenient handling of large quantities
of lamps.
Several candlepower scales are mounted on a brass drum which
4 This arrangement of the comparison lamp and of a special resistance, described
later, were introduced by Ives and Woodhull, who, for a short time, were associated with
this work. See Bulletin of Bureau of Standards, vol. 5, p. 555.
5 Brooks, H. B., A New Potentiometer for the Measurement of Electromotive Force
and Current; Bulletin of the Bureau of Standards, vol. 2, p. 225, 1906.
MIDDLEKAUEF, MULLIGAN, SKOGLAND : TESTING OE LAMPS 821
fits within the front tube of the track. The normal scale is used
when the photometer receives unmodified light from both test and
comparison lamps. The choice of other scales depends upon the
opening of the sectored disk8 or the transmission of the glass
screen used and upon whether these auxiliaries are used on the
test or on the comparison side of the photometer. In routine work
these scales are used only in calibrating the photometer, because
the equipment installed eliminates all reference to actual values
on the scales.
(c) Wiring and Special Resistances. — As shown in Fig. 3, the
test and the comparison lamps are wired in separate circuits in
order to permit a wide voltage range on the former without af-
fecting the voltage on the latter. In the comparison lamp circuit,
besides the adjustable rheostat R2, there are two special resis-
tances designated by R3 and R4, respectively. The purpose of
these special resistances is to maintain the comparison lamp at
certain definite colors and still permit a precise calibration of the
photometer in terms of the group of standards used without
making tedious experimental adjustments of resistance.
With the resistance R3 all in circuit the comparison lamp
operates at the color of carbon test lamps. With a fixed amount
of R3 short-circuited by the switch SW, a color used in the
measurement of tungsten lamps is obtained. When the standards
are operated at the same color as the test lamps, a color match
with the comparison lamp is obtained by placing a blue glass
screen (the percentage transmission of which need not be known)
on the comparison side of the photometer. This is done in
order that the comparison lamp may be operated at a compara-
tively low efficiency and thus prolong its useful life. In case it is
desired to run test lamps at an efficiency higher than that which
would be safe for the standards, a glass screen of known trans-
mission must be used with the comparison lamp while measuring
the test lamps, but in calibrating the photometer the screen is
replaced by the sectored disk so set that the percentage opening
is equal to the coefficient of the screen. In this way the standards
are operated at the unmodified color of the comparison lamp
and the test lamps at any desired color for which a color screen of
* For all work on this photometer an adjustable sectored disk is used.
822 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
the proper density for color match with the comparison lamp is
selected.
The potentiometer button 2., to which the galvanometer is
switched in setting the comparison lamp, is connected to contact
P on the slide-wire resistance R4 which will be described pres-
ently. In the position shown it is evident that the drop from P
across the portion of R3 in circuit is measured. This drop is
proportional to the current in the comparison lamp circuit, and
hence by a proper choice of resistance R3 (which is large in
comparison with R4) the exact current in the comparison lamp
for carbon color is obtained. As the voltage on the standards or
test lamps is set with the switch lever on button I, a check can be
kept on the current in the comparison lamp without disturbing the
potentiometer setting by simply switching the lever to a button 2.
Any necessary adjustment in the current is made by means of
resistance R2 to bring the galvanometer pointer back to zero.
In calibrating the photometer the adjustment of the comparison
source is easily made to within 1 or 2 per cent, in candlepower
by means of the adjustable shutter on the ground glass window.
The final adjustment is made by moving contact P along the
slide-wire resistance R4 a distance corresponding to the desired
small change in candlepower as read from a scale of candlepower
differentials placed under the wire. The changes of current pro-
duced by moving P are small, so that the changes in color of
the comparison lamp thus produced are entirely negligible. Ives
and Woodhull7 made use of an adjustable resistance but the null
method made possible by the modified potentiometer connections
and the calibrated slide- wire resistance just described was in-
troduced later.
(d) The Watts- per-Candle Computer. — Two sets of special
scales are used in connection with this photometer. One set is
used in computing watts-per-candle from the observations while
the other set is used in connection with a recording device. The
w. p. c. computer, which operates on the principle of an ordinary
slide rule, consists of an ampere scale and a w. p. c. scale both
logarithmic and calculated on the same base.8 These are placed
7 .See note 5, p. 7.
8 The base of a common logarithmic scale is the distance from 1 to 10, 10 to 100, etc.,
on the scale.
MIDDLEKAUFF, MULLIGAN, SKOGLAND : TESTING OF LAMPS 823
parallel to the photometric axis between the photometer head
and the carriage, the w. p. c. scale (showing white in Fig. 1) being
attached to the carriage so as to move with it.
The design of the computer is based upon the fact that a
logarithmic scale may be constructed which practically coincides
with the candlepower scale over a range extending from one-half
to double the candlepower reading at the middle of the scale.
The base of such a logarithmic scale for a 250 cm. photometer is
71.25 cm. and the maximum differences of a scale so constructed
from the true candlepower scale, the middle division of which is
20 candlepower, are only 0.08 cm. corresponding to about 0.25
per cent, in candlepower and occurring at approximately the 14
and 28 candlepower divisions. These differences, even at the
points of maximum value, are entirely negligible for the purposes
of this photometer and the advantages gained by employing the
logarithmic scale fully offset the small errors introduced.
The two parts of the computer are logarithmic scales con-
structed in this manner, but the divisions are labeled amperes and
w. p. c. respectively, instead of candlepower.
Now, it is evident that, with the photometer set to a given can-
dlepower, the ampere scale may be moved horizontally to a point
where for a given voltage the corresponding w. p. c. will appear
under any chosen value of current (which then corresponds to the
wattage), and that after this setting the correct w. p. c. value will
appear under the corresponding current at all points of the scale.
Now if a lamp is run at this same voltage and the photometer is
moved to the point of balance the correct w. p. c. will still appear
under the observed current, because the w. p. c. scale attached to
the photometer carriage has been moved in its relation to the
ampere scale by a distance corresponding to the change in can-
dlepower. The ampere scale must be reset for every change of
voltage but by proper grouping of lamps a large number may be
run in succession at one voltage, so that these changes are infre-
quent during any single run.
(e) The Recording Device. — The recording device consists of
a stamping magnet, a cylinder carrying a number of scales, and a
car for holding the record cards. The magnet and cylinder are
attached to the photometer carriage and therefore move with it.
824 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
The cylinder is mounted normal to the photometric axis and
carries three lorarithmic scales running parallel to its length, one
being an hour scale, the other two being w. p. c. scales for use in
measuring tungsten and carbon lamps, respectively. The magnet
is supported by a rod placed parallel to the cylinder, so that the
pointer carried by the magnet may be set at any division on any
one of the three scales, the desired scale being presented by turn-
ing the cylinder.
The car may be moved on a track parallel to the photometric
axis but is held at any one of a number of nearly equally spaced
points by means of a pin placed in a corresponding hole in the
track. The distance between any two adjacent holes corresponds
to half the distance from 100 per cent, to 80 per cent, candle-
power as read from the true candlepower scale. These holes are
labeled with two series of the same letters, one series being printed
in red, the other in black, the letters of the red series being placed
two spaces nearer the comparison lamp than the corresponding
letters of the series in black. The use of these letters will be
described presently.
The observations are recorded as points stamped on plain white
cards approximately 12.5 cm. by 20 cm., there being one card for
each lamp (see Fig. 4). These are placed in the car with their
long dimension normal to the photometric axis and therefore
parallel to the scales on the cylinder. Now it is evident that the
short dimension of the card may be looked upon as a candle-
power scale and the long dimension as an hour scale or a w. p. c.
scale depending upon which of these two quantities is to be meas-
ured and recorded. The position for the card on the photometer
is so chosen at the initial measurement that the candlepower
record will be made sufficiently high to permit all values during
the life of the lamp to fall on the card. This is regarded as the
normal position of the card and is designated by the correspond-
ing black letter which is then written on the card. The card is
placed in this position during all but the initial measurements,
the reason for this exception being given in the following section.
The two most important quantities to be recorded are the
initial (test) w. p. c. and the life. The latter is defined as the
number of hours required for a lamp to reduce to 80 per cent, of
Fig. i. — The life test photometer.
Fig. 2.— Transformers, switchboard and life racks.
*4
WIMVWWMAA — £
Potentiometer
From storage Battery
y
iv
'\/V\UvV\M/WVWMWAMWvv\AMWV\MMM/\A\M
-<r
I?
Fig. 3. — Wiring diagram of the life test photometer.
[Cord Position on Photomt ter Bench)
'^Ill-flour Readings)
'AZI -//our Readings]
'•(/S7-//our Readings)
(liJeTesl Lot/Co)
[Test /oils)
471 120
(M>th)~°
(Candlepo^'. (,nde* of //our Scale),
3 hours 4 5 S\7 0 3 iJJ
Record of Test Vpc)
'II /
■^-V (80-/. C/> Line)
(Lamp Wo)
38N4310
/ 1
(Life at loo ¥/>c - 7S7firs) \
1
(Test Life -SOS Urs)
z J Hours 4
(Mean Test Wpc -0.3467) 1 —
5 6,7 691
k/at/s Per Candle
Fig. 4.— Completed test record on a lamp card showing the scales used in placing the
record points and in evaluating corrected life.
MIDDLEKAUFF, MULLIGAN, SKOGLAND : TESTING OF LAMPS 825
its initial candlepower, or to burn out, if within that period.
Now it is evident that, so far as making the record is concerned,
motion of the card toward higher candlepower on the photometer
is equivalent to moving the photometer in the opposite direction.
If, therefore, during the initial measurement of candlepower the
card be set, not at its normal (black letter) position, but at that
designated by the corresponding red letter, the record point of the
observed candlepower will fall at a position corresponding to 80
per cent, of the value observed. This point therefore establishes
on the record the limiting line of life as defined by the specifi-
cations.
As the record of the initial measurement does not include the
element of time, it may be made at any point along the 80 per
cent. line. Hence, if the stamping magnet be set at the point on
the w. p. c. scale (which scale for tungsten lamps is reproduced
under the card in the figure) corresponding to observed initial
w. p. c, not only 80 per cent, of the initial candlepower but also
the initial w. p. c. as well may be recorded by the same point. To
distinguish these initial points from the rest of the records, they
are stamped in red (indicated by -f- in the figure) while all the
others are stamped in black. For all but the initial measurements
the card is set at the black letter position and the magnet is set
at a point on the hour scale (which scale is also reproduced under
the card in the figure) corresponding to the total number of
hours the lamp has burned. The candlepower-hour record points
are stamped in succession across the card as many times as neces-
sary, the hour scale reading for each succeeding series being ten
times the value it had in the series next preceding. The complete
record thus obtained on any card graphically represents the per-
formance of the corresponding lamp and the actual test life is
indicated by the point of intersection of the curve of candlepower
performance with the 80 per cent, candlepower line.
So far as obtaining a record is concerned, any scale might have
been adopted for use on the cylinder in recording test life and
initial w. p. c, but the scales here employed have been so chosen
in respect to their relative lengths and relative position on the
cylinder as to permit the evaluation of corrected life from test
w. p. c. to rated w. p. c. directly from the card record without
826 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
computation or reference to tables of factors. This arrangement
was based upon the following considerations.
It has been shown that within certain limits the relation be-
tween life and w. p. c. may be expressed by the formula,
Life ratio = (w. p. c. ratio) m (1)
in which m has been found to have a value of about 7.4 for
tungsten lamps and 5.83 for carbon lamps. From equation (1)
is derived
log life ratio = m log w. p. c. ratio (2)
analogous to the equation
y = mx (3)
which is the equation of a straight line. Hence a logarithmic
hour scale and a similarly constructed w. p. c. scale with a base
equal to m times the base of the hour scale may be used together
as a slide rule for making life corrections from one efficiency
to another. Life in hours on the one scale is set opposite the
corresponding w. p. c. on the other, and life at any other w. p. c,
not exceeding the limits through which m has a constant value, is
read by referring to the corresponding w. p. c. division.
The hour scale on the cylinder of the recording device was
plotted to a base of 20 cm. (equal to the approximate length of
the record cards) with divisions from 1 to 10, as in all slide-
rule scales, and hence the base taken for the w. p. c. scale for
tungsten lamps was 7.4 X20= 148.0, and for carbon lamps,
5.83 X 20= 1 16.6.
Life requirements in the specifications are expressed in hours
as rated w. p. c. As rated w. p. c. is not the same for all sizes of
lamps of any class and is subject to change from year to year, it
was considered best, in constructing this device, to arrange for
life correction to a certain chosen w. p. c. value for each class of
lamps, and by means of equation (1) compute for all sizes of
the same class the required life at this chosen w. p. c. Accord-
ingly 1. 00 w. p. c. was chosen for tungsten lamps and 3.05 w. p. c.
for carbon lamps. The life of any lamp, or the mean life of any
group of lamps of the same size, is then expressed in per cent, of
the required life.
MIDDLEKAUFF, MULUGAN, SKOGLAND : TESTING OF LAMPS 827
The logarithmic hour and w. p. c. scales constructed as above
described, were then so placed on the cylinder that the 1.00 w. p. c.
division of the tungsten scale was in line with the 1,000-hour di-
vision of the hour scale, as shown in Fig. 4, and the 3.05 w. p. c.
division of the carbon scale in line with the 450-hour division.
The w. p. c. points on the card are thus recorded on a logarithmic
scale and in a definite relation to the hour scale. Now if the 1,000-
hour division of the scale in the case of tungsten lamps, orthe450-
hour division in the case of carbon lamps, be taken as an index and
a duplicate of the hour scale be placed, as shown in Fig. 4, with
the proper index on the mean of the w. p. c. points of the record
and with its reading edge on the 80 per cent, line, the test life,
corrected to the chosen w. p. c, may be read at the intersection of
the scale and the candlepower performance curve.
In case a lamp burns out above 80 per cent, of its initial candle-
power value, a vertical line is drawn across the 80 per cent, line
at the proper point as determined by the life test log and the
hour scale, but the procedure in obtaining corrected life is the
same as in the case of lamps which have burned to 80 per cent.
For lamps having other than the specified mean spherical re-
duction factors, the index may be so chosen that the correspond-
ing difference is made in the corrected life. Certain special
lamps, for example lamps in tubular and round bulbs, are thus
evaluated.
(/) Features of the Record. — (a) Detection and Compensa-
tion of Errors. — One characteristic of these record points of the
initial readings of w. p. c. and candlepower (Fig. 4) is of interest
and importance in that it serves as a visual check upon the cor-
rectness of the records. Rarely do two observers on the photom-
eter check each other exactly, but the precision of electrical in-
struments and the constancy of electric lamps during the rela-
tively short time they are in circuit on the photometer are such
that the ampere reading is usually repeated to within 0.001. Sup-
pose now that at the same current the second observer reads a
candlepower value higher than that recorded by the first. The
w. p. c. computer will, consequently, indicate a lower value, since
the candlepower is higher for the same watts. Referring to Fig.
4 it will be seen that the second point will be placed above and to
15
828 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
the left of the first. For a candlepower reading lower than the
first, the current remaining the same, the point will be placed
below and farther to the right. Supose, now, that one or other of
the ampere readings is in error, the second being appreciably
higher than the first. The apparent w. p. c. of the second observa-
tion is then higher than it should be, regarding the first as correct,
and the effect is to change the slope of the line connecting the rwo
observations. Displacements may occur also in case of errors in
transfer to the record card or as combination of errors.
Now it is evident that the equation
Watts = cp. X w.p.c. = constant (4)
expresses, for a steady lamp, the condition for correct reading.
This is the equation of an equilateral hyperbola. Although some-
what modified by the logarithmic scale of the recording equipment,
it is closely approximated in form by correctly recorded points
under conditions of constant watts ; so that the slope of the line
connecting the initial w. p. c. points may be used as an indication
of their precision, and any considerable deviation from the correct
slope indicates that some error has been made. Any lamps, the
records of which, show such deviations are, therefore, re-photom-
etered.
Another interesting feature of the card record of a normal lamp
is that the slope of the candlepower-life curve between its last
two points is often very nearly the same as that of the line join-
ing the two initial w. p. c. points ; consequently in these cases com-
paratively large differences in distance between initial points
effect no considerable change in corrected life, which may be
evaluated with small error from any point in the line connecting
the w. p. c. points. Observational errors in initial readings are
therefore always compensated for to some extent by the fact that
the candlepower-life and initial w. p. c. curves always slope in the
same general direction. It is doubtful if any other than this
system of photometry and recording posesses these advantages.
(/?) Increased Accuracy in Life Values. — In evaluating lamps
which have burned to 80 per cent, a straight line is drawn
between the last two points on the record cards, one of which
is above and other below the 80 per cent, candlepower line
(Fig. 4). If this line be transferred to rectangular co-ordinates
MIDDLEKAUFF, MULLIGAN, SKOGLAND : TESTING OF LAMPS 829
it will be found that it is slightly curved, being convex downward
toward the life axis. As this is characteristic of a true candle-
power-life curve, this method gives, on an average, a closer
approximation to the actual time of crossing the 80 per cent, line
than that obtained by direct interpolation.
2. Methods of Measuring and Recording Observed Values. —
(a) Rating of Lamps for Life Test. — Two methods are in com-
mon use in rating lamps for life test. The first distinguishes
two voltages, namely, "photometer" voltage, which usually cor-
responds to rated voltage, and "rack" voltage. Rack voltage is
computed from photometer voltage and the corresponding w.p.c.
by the characteristic equation expressing the relation of volts
to w. p. c. By this method the lamps are always run on the
photometer, both initially and during life test, at photometer
voltage. They are operated on life test at rack voltage, which of
course correspond to test w. p. c. within the desired limits. By
the second method the lamps are photometered and operated on
life test at rack voltage. In the case of vacuum tungsten lamps,
the characteristics of which are well known, either method may
be used. Advocates of the first method claim advantages for it
in the greater certainty of candlepower observations made at or
near a color match with the standards. These are no doubt real
advantages, as there is now practically no uncertainty introduced
by computations based on well established values within certain
limits of w. p. c. for normal lamps.
The Bureau, however, employs the second method. Although
this method was adopted before the characteristics of tungsten
lamps were as well known as they now are, it is still used be-
cause it introduces no uncertainties due to possible failure of any
lamps to conform to the characteristic relations. Although an
extra scale for reading rack voltage could easily be added to those
above described, thus permitting measurements at photometer
voltage, a careful investigation of the possible added advantages
thus secured as weighed against a somewhat greater complexity
of apparatus and consequent added liability of error would first
have to be made, if a change to the first method should ever be
contemplated.
(b) Details of a Photometric Run. — As a Lummer-Brodhun
83O TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
photometer is used, all measurements are made at as nearly a
color match as possible. By the method at present in use, the
photometer is always calibrated by six tungsten standards se-
lected at random from a much larger group. The values of
candlepower and current for the individual lamps of this group,
over a wide range of voltage (and color), are tabulated on a
card within view of the electrical operator and in what follows
these are designated as "certified" values. The comparison lamp
is adjusted in current so as to give the proper color to match the
lamps to be tested, this being done by simply balancing the po-
tentiometer against the voltage drop across resistance R3 (Fig. 3),
the small adjustment necessary being made by means of resis-
tance R2. Switch SW is open or closed, depending upon whether
carbon or tungsten lamps are to be measured. The first standard
is then placed in the socket and adjusted in voltage to match the
modified or unmodified color of the comparison lamp depending
upon the efficiency at which the test lamps are to be measured
(see p. 821).
After the color adjustment, the certified candlepower value
of the standard, at the voltage to which adjustment was made,
is called off by the electrical operator, and the photometer oper-
ator so adjusts the shutter on the ground glass window which
fronts the comparison lamp-box that a balance is secured at
approximately the certified value as read on the candlepower
scale. After this approximate calibration, a stamped record of
about ten individual settings is made for each of the six stand-
ards. After the observed values of a standard are recorded, the
certified value is called off by the electrical operator and, with
the photometer set at this point on the scale, this value also is
stamped on the card. A copy of a short section of the candle-
power scale is used to read off the algebraic differences between
the certified and the observed candlepower values. In this man-
ner the difference between observed and certified values of all the
standards are determined and the mean difference is computed.
Correction for this mean difference is then made by moving the
sliding contact P of the resistance R4 (p. 822) the proper number
of scale divisions. This necessitates a small adjustment of the
comparison lamp current which is now made by means of re-
MIDDLEKAUFF, MULLIGAN, SKOGLAND : TESTING QF LAMPS 83I
sistance R2. The electrical operator has, in the meantime, com-
pared the observed current with the certified current and deter-
mined a mean correction for ammeter readings ; or, in case lamps
whose ampere readings are considerably different from that of
the standards are to be run, the proper ampere standard is selected
from a group of seasoned lamps used only for this purpose, and
the mean ampere correction thus established is applied throughout
the run. The standard check is the last direct reference made to
actual values on the candlepower scale.
Having determined by trial the even voltage, {e. g., 118, 120,
etc.) corresponding to a dial setting on the potentiometer at which
the first test lamp falls within the desired range of test w. p. c,
the ampere scale is set to a point corresponding to this voltage
(see p. 823). Opposite the ampere value called off by the elec-
trical operator is read the test w. p. c. With the card so placed
that the value to be recorded will be at least two-thirds
of the way down the card, the index carried by the stamping
magnet is set at the observed w. p. c, the circuit through the
magnet is closed by pressing a button, thus making the record
of the w. p. c. and also 80 per cent, of the candlepower as a
single point in red. The red letter indicating the card position is
noted and a card bearing this letter is selected from the file
within reach and placed face down on the photometer bench, the
first record card being turned over and placed upon it. As the
different lamps are photometered the corresponding lamp cards
and position cards are added in regular order. The same voltage
is applied to each lamp in succession until one is reached which
requires a change of voltage, when the ampere scale is reset to
correspond to this voltage. Readings are continued at this new
voltage to a point where another change of voltage is required,
etc. "Information cards" designating voltage, disk opening,
card position, etc. are introduced in the proper place to indicate
the changes to be made in succeeding measurements.
The photometer calibration is checked by two or three stand-
ards at intervals during the run and the indicated changes of
comparison lamp current are made when required (p. 822).
After the first run, cards for lamps of the same voltage, disk
opening, card position, etc. are grouped together to the best
832 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
advantage, the extra information cards being removed and filed
for future use. The life-test lot number, the voltage, and position
letter are then printed or written on each card, and the lamps re-
arranged for a second run in the order determined by the card
positions, thus facilitating the work. After the second run, for
which the two operators exchange places, such additional check
measurements, as are found necessary (p. 828), are made. The
lamps are then ready for the life test racks where they are burned
at the respective voltages found.
After the first period of burning on the life test, the lamps are
removed, placed in the proper order and again run on the photom-
eter at the test (rack) voltages. The cards are now set to the
black letter position (p. 824) indicated on the information cards
and on each lamp card, and the stamping-magnet index is placed
at the point on the hour scale corresponding to the number of
hours the lamps of the lot have burned.
The ampere scale is set as in the initial run, and, after the ob-
served candlepower value is recorded, the photometer is set so
that an index on the movable part of the w. p. c. computing device
is opposite the observed current value and a record of the position
is stamped. As the voltage at every measurement of a given lamp
is the same, this record shows the variations in the watts during
the life of the lamp. (These points are surrounded by circles in
Fig- 4-)
Measurements are made in this manner after each test life
period until all lamps of the lot have crossed the 80 per cent,
candlepower line or burned out above it.
THE LIFE TEST.
1. Design of the Installation. — At the time when the design
of the life test equipment was under discussion, the common
method in use elsewhere of setting individual lamps or racks of
lamps to a desired test voltage was by means of a resistance
in series with each lamp or rack. The disadvantages of this
method were apparent, and search was therefore made for an
arrangement of equipment which would be free from these dis-
advantages but which would still conform to the requirements
to be met. An arrangement of auto-transformers proposed by
Mr. Brooks was adopted because of its simplicity, convenience,
and general conformity to the requirements of life-test operation.
MIDDEEKAUFF, MULLIGAN, SK0GLAND : TESTING OF LAMPS 833
Other laboratories have since adopted the essential features of
this arrangement which are fully described below.
1. Wiring and Voltage Adjustment. — Referring to the wiring
diagram, Fig. 5, which exhibits the essential features of the sys-
tem, it is seen that alternating current is supplied by the genera-
tor to the center of distribution. Auto-transformers T1 to T4
■From Generator
Fig. 5. Wiring diagram of the switchboard and life racks.
supply current to the bus-bars at the voltages indicated.9 These
bus-bars are mounted on the back of the switchboard panel to the
right of the clock (Fig. 2). One terminal of each rack (hori-
zontal row) is connected to the common bus through the second-
ary of a regulating transformer B; the other terminal is con-
nected to a plug hole in this same panel. Hence, to energize a
9 No provision has yet been made for low voltage or series burning lamps.
834 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
given rack R a connecting cable is plugged from the correspond-
ing plug hole to the bus maintaining the voltage nearest to that
desired. The conductors from the switchboard to the racks are
of No. 4 wire carried through ten lines of 2-inch conduit running
over the tops of the switchboard and racks to junction boxes
from which connection is made to the terminals of the copper
rod conductors of the racks.
The special auto-transformer ST maintains voltages of +5,
+ 10, -+-15 to +50, and corresponding negative voltages on bus-
bars located on the front of the middle panel. One primary
terminal of each of the regulating transformers B ends in a cor-
responding plug hole also on this panel. As the ratio of trans-
formation of the regulating transformer is 5 to 1, it follows
that -f- or — changes of 1,2, 3, to 10 volts may be made effective
on the rack. Hence, by plugging from the transformer terminal
to the proper bus-bar on this panel, a second approximation to
the exact voltage desired on rack R is obtained.
The other primary terminal of each of the regulating trans-
formers ends in the lever of a corresponding dial switch S located
on the left panel of the switchboard. The buttons of each switch
are maintained one volt apart over a range of 10 volts, by leads
from adjacent one-volt subdivisions of transformer ST, but be-
cause of the 5 to 1 transformation in B each volt at the switch
is effectively 0.2 volt on the rack. Hence, by properly setting
the switch the exact voltage desired is approximated to within
0.1 volt.
The voltage of each rack is adjusted at the switchboard by
reference to a portable voltmeter which may be connected to the
corresponding pair of binding posts forming the terminals of the
potential leads V from the center of the rack. The voltage of
a rack is thus adjusted by actual measurement in every case.
Each pair of binding posts appears on the corresponding dial
switch. As these switches are grouped on a single panel, any
number of racks may be quickly set without inconvenience with
the voltmeter kept in a fixed position on its stand.
(b) Voltage Regulation. — A Tirrill regulator, which operates
by periodically short-circuiting a resistance in series with the
exciter field, maintains the voltage at the center of distribution
MIDDLEKAUFE, MULLIGAN, SK0GLAND : TESTING OE LAMPS 835
in the life test room constant to within the limits of plus or minus
one quarter of 1 per cent, as required by the specifications. A
continuous record of this voltage is obtained on an accurate
recording voltmeter located in the dynamo room.
(c) Current Generator and Voltage Transformers. — The gene-
rator which supplies current for the life test is a 40 kw., 125-volt,
360 r. p. m., single-phase, rotating-field alternator, directly con-
nected to the driving engine, the exciter being mounted upon the
same shaft. Transformers B (shown back of the switchboard
in Fig. 2) are one-half kw., air-cooled, shell-type; while ST and
Tx to T4 are oil-immersed, auto-transformers of the capacities
indicated in Fig. 5, the relative capacities of Tx to T4 being
roughly in proportion to the number of lamps usually run at their
respective voltages.
(d) The Life Test Racks. — The supporting frames of the racks
are built up of steel members consisting of vertical end posts of
channel section and equally spaced intermediate posts of I-beam
section connected by heavy angles to horizontal top and bottom
pieces of channel section, the whole being supported by cast iron
feet bolted to the composition (tileine) floor. Bolted to each side
of the vertical members are six equally spaced horizontal strips of
asbestos board which support porcelain cleat sockets, spaced on
12 in. (30.5 cm.) centers, with soldered electrical connections to
copper rods 5 mm. in diameter. Midway between each pair of
these sockets, which are arranged for burning the lamps in a
horizontal position, conducting straps are soldered at one end
to the 5 mm. copper rods and at the other end to the terminals
of porcelain cleat sockets arranged for burning lamps in a ver-
tical position. The long racks (17 ft. (5.18 m.) ) have 31 sockets
on each side; the short racks (13 ft. (3.96 m.) ), 23. On a few
of the lower racks the sockets for vertical burning are spaced
on 18-in. (45.7 cm.) centers. The large lamps burned on these
racks are thus kept well separated during life test. The total
number of vertical sockets is 1,200 and of horizontal sockets,
1,296.
The eight stacks of racks are spaced 4 ft. 10.5 in. (1.49 m.)
apart, which gives a symmetrical arrangement in the life test
836 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
room with sufficient space to permit safe and convenient handling
of lamps.
(e) Measurement of Life Test Periods. — An important detail
in conducting a life test is the accurate measurement of the time
the lamps have burned. For this purpose an electric clock which
measures time in hours from one to one thousand is used. This
clock is connected in the master clock circuit of the Bureau
and is short-circuited by a relay when the power is cut off. The
log of any life test contains the clock time to the nearest 0.1
hour, corresponding to the time of placing the lamps on and
removing them from the rack circuit. The time of burnouts
during the night is either recorded by the watchman who visits
the room every two hours, or the lamps are considered as having
burned until 9.00 o'clock the following morning.
2. Records Taken During Life Test. — Summarizing the records
which are taken during life test, as described above, it will be
found that the following have been mentioned :
(a) Test voltage; initial candlepower and initial w. p. c. at test
voltage.
(b) Candlepower and watts at certain periods during test life.
For carbon and metallized filament lamps the specifications re-
quire measurement after approximately 50 hours of burning and
"at least every hundred hours thereafter" throughout useful life.
Five measurements, the first approximately one-twentieth of the
test life period, after the initial are specified for tungsten lamps.
(c) Recording voltmeter records of main life test voltage.
(d) Test log showing clock reading from which test life
periods are computed.
In addition to the above there are, of course, required such
other records as will permit orderly clerical procedure. A card
record system is used throughout, but the details, which have
been worked out to take care of features in some cases peculiar
to the Bureau tests only, would hardly be of general interest.
SUMMARIES OF LIFE VALUES.
After the completion of a sufficient number of test lamps to
warrant quality comparisons, life values of lamps of the same
type, size, and manufacture, and of a voltage range through which
a given life value is specified, are averaged. A summary giving
MIDDLEKAUFF, MULLIGAN, SKOGLAND : TESTING OF LAMPS 837
the date, type, size, manufacture, voltage range, number of
lamps, corrected life and percentage of required life is prepared
from these data, so that a manufacturer may, at his request, refer
to the summary for information regarding the quality of his
lamps and those of other manufacturers supplying lamps under
the annual contract. In case lamps are rejected as the result of
life test the manufacturer and purchaser are promptly notified,
each being given the life value on which rejection is based.
Additions of other lamps are made to this summary from time
to time, so that average quality values to the corresponding date
are indicated; except, that in case of a drop in quality of certain
items so decidedly below the required life that rejection of the
defective lamps is necessary, the figures for accepted and rejected
lamps are kept separate until the end of the tests, when the
average life of accepted and rejected lamps combined is reported
as a final value.
DISCUSSION.
Mr. Leonard J. Lewinson : As one "life tester" to another,
I want to express my appreciation of this paper. The authors are
to be congratulated on their able exposition of the subject, on the
admirable detail of the equipment at their disposal and on their
system of records.
There is no mention in the paper of measurements of mean
spherical candlepower. At the laboratories with which I am con-
nected integrating spheres are an essential part of the equipment.
For filaments of different conformations, total flux measurements
have always been necessary, even in the days of the old carbon
lamps, and now that the gas-filled lamp has come into existence,
the need is strongly emphasized. We make it a practise to test
all gas-filled lamps on a mean spherical basis, and find very con-
siderable changes in the spherical reduction factor throughout
life. Even in the vacuum type, we have detected such changes,
though of a rather small order in the lamps as constructed at
present. Some of our vacuum lamp life tests are now on a
spherical candlepower basis, and we expect to be making all life
tests on this basis in the course of the next year.
As the authors state, some life testing organizations measure
838 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
lamps at an arbitrary voltage, usually the labeled voltage, and
calculate the rack voltage, or voltage at which they are to be
burned on life test. At the Bureau of Standards, however, the
actual test voltage is measured. This practise is to be endorsed.
At the Electrical Testing Laboratories we use both methods, even
in forced tests, employing the calculated voltage as an approxi-
mation and the actual measured voltage as the correct test value.
At the Bureau, the tests are made on a 60-cycle current. At the
Laboratories the majority of lamps are operated under similar
conditions ; in addition, at least once a year we test a substantial
number of lamps on direct current. At present we are also en-
gaged in testing several groups of carefully selected lamps at 30,
40, 60, 90, and 150-cycles.
From the statement at the foot of the fifteenth page, it appears
that tungsten lamps are tested at the Bureau at about 1 .0 watt per
candle. Above, on the same page, the relation of life to watts per
candle is expressed as a parabolic curve with an exponent of
7.4, with a qualification to the effect that the equation is limited
in its use to a certain range of watts per candle. Now small
tungsten lamps, 10 and 15-watts, are rated at 1.35 to 1.15 watts
per candle, so that it would appear that a test at 1.0 watt per
candle is in effect a considerably forced test on these small lamps.
I should like to ask the authors what their experience has been
in reference to the applicability of the correction factor based on
the 7.4 exponent in tests on such small lamps ?
Mr. J. L. Minick : The Pennsylvania Railroad is one of the
few large corporations that makes a careful inspection and test
of the incandescent lamps purchased for its use. It may be of in-
terest to some of you to know that their routine method of inspec-
tion and test follows closely that established by the Bureau of
Standards. Their laboratory equipment, however, is not so
elaborate and probably not so accurate as that used by the Bureau,
though check tests with the Bureau and other laboratories show
that very accurate work is being done at the Altoona laboratory
of the railroad. The remodeling of the laboratory equipment has
been under consideration for some time, but prospective changes
in lamp design seem to warrant postponing definite action until it
can be determined whether the rating of lamps will be changed
TESTING OF LAMPS 839
from a "mean horizontal" to a "mean spherical" candlepower
basis.
I am sorry that the authors of this paper have not touched upon
this phase of their work. The introduction of the gas-filled lamp
will undoubtedly make it necessary to abandon "mean horizontal"
candlepower as the basis for rating lamps. This will bring about
changes in routine methods of inspection and test and will
probably require changes in laboratory equipment and it is essen-
tial that the Bureau of Standards, which is accepted by the manu-
facturers and most of the large purchasers as the arbitrator in
case of dispute, be prepared to offer advice concerning the
changes indicated above.
The Pennsylvania Railroad practise differs from that of the
Bureau of Standards in that they depend largely upon forced or
excess voltage tests to determine whether the life performance of
the test samples is satisfactory or not. The excess voltage life
values used are determined from the formula quoted by the
authors, that having the exponent 7.4. The average test life of all
lamps tested throughout a period of some four or five months
checks very closely with the values determined from the formula,
though many individual tests show rather wide variations.
Mr. P. S. Millar : I should like to add a word of commenda-
tion of this paper. The authors have succeeded in presenting
very clearly an excellent description of the life testing system,
which is very highly developed. They have refined mechanical
and electrical details in a way which I presume contributes to ac-
curacy and economy. I believe they have an excellent system and
are doing very good work.
Just a word of a general nature on this question of lamp life
testing. There prevails in many quarters the notion that if a few
lamps of a number of different brands are subjected to tests,
the result will be an adequate guide for purchasing purposes.
That is not so. You will note that this paper states that the tests
are spread over a million and a quarter lamps. Mr. Minick in
describing the tests of the Pennsylvania Railroad states that the
purchases are on the order of a million lamps per annum. When
purchasing in such quantities, lamp life tests can be made very
valuable. In small purchases it is impracticable to conduct life
840 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
tests which will result in ultimate economy. It is important in
any life testing of lamps to know the real cost of the work and to
compare such cost with the value derived from the test in im-
provement of the quality of the lamp obtained for use.
There are three questions which I should like to ask the authors
regarding not so much the details of life testing as the general
principles of the conduct of such a test. I ask them because the
same problems have come to me and I have found difficulty in
meeting them. If two groups of, let us say, 6 incandescent lamps
of two different brands are submitted to the Bureau of Stand-
ards for life test, I should like to ask what action the Bureau
takes. Do they test the lamps ? Do they qualify the report in any
way when the report is rendered ? Second, if two such groups of
lamps are presented for tests and the lamps of one group were
manufactured to be operated at one and seven hundredths watts
per candle and the lamps of the other group were manufactured
to be operated at one watt per candle, and the groups are of dif-
ferent brands, what action does the Bureau take in regard to
tests and results? Are both groups operated at one watt per
candle, or are they operated at the respective watts per candle for
which they were intended ? Third, if two such groups were pre-
sented for tests and the Bureau does not know at what watts per
candle they were intended to be operated, what action is taken in
the running of the test and the preparation of the report? These
are very important questions and questions of a very practical na-
ture, and I am frank to say that I hardly know what is the right
answer.
Dr. C. E. MeEs: With regard to Mr. Millar's point as to
the testing of lamps in small establishments, I will point out that
there is another side than the question of whether a saving could
be made on the cost of lamps. In a good many manufacturing
establishments bad lamps are not replaced as adequately as they
should be when their efficiency gets down. Their replacement is
sometimes difficult because of the nature of the work. It is
sometimes difficult to take out lamps, as in our case, the Eastman
Kodak Company, and in other cases the efficiency of the depart-
ment replacing the lamp is not all it should be; so that bad lamps
are a source of more cost than is apparent owing to the insuf-
TESTING OF LAMPS 84I
ficient light leading to bad and inefficient work : in many cases I
believe that a properly conducted life test on all lamps purchased
would pay, even though the cost of the test was greater than
the actual saving made. We only use a tenth as many lamps as
the Pennslyvania Railroad, but it still pays us to test lamps on the
life test.
Dr. E. B. Rosa : We do not make such tests as Mr. Millar de-
scribes and therefore do not have the difficulty that he has. Our
testing is almost entirely for the government ; it is only occasion-
ally that we make other tests than for the government, and those
are for very special reasons. If we should make such tests, we
should guard our statements very carefully indeed, and say that
the results are for the particular lamps submitted and that no
conclusions should be drawn for other lamps not included. As a
rule, when we have made tests for others than the government,
it has been on a much larger number of lamps.
Dr. G. W. Middlfkauff: In reference to the question of the
measurement of mean spherical candlepower, I would say that,
up to the present, measurements of this kind have not been neces-
sary in our work. The reason for this is that, in accordance
with standard specifications, all vacuum tungsten lamps are
tested on the basis of mean horizontal candlepower; and, with
few exceptions, all carbon lamps tested have been of the regular
sizes the reduction factors for which are well established. For
the few special sizes of carbon lamps tested, the reduction factors
are determined and the proper corrections are made in the rating.
Furthermore, there have been so few gas-filled lamps purchased
by the government that the number of samples selected during
inspection has been entirely too small to justify the expense of
testing them. However, the indications are that within the very
neat future we shall be testing gas-filled lamps also, and, when
we do, it is our intention to test them on a mean spherical basis.
We have done considerable work on the determination of the
life-efficiency exponent for various sizes of vacuum tungsten
lamps, a certain number of which each year are tested at or near
normal w. p. c, but we do not have at present sufficient data on
the 10 and 15 watt sizes to draw a definite conclusion. However,
842 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
the indications are that the exponent which applies to these
smaller sizes is somewhat less than 7.4.
Although it is not mentioned in the paper, our tests of tung-
sten lamps have been made at 0.9 to 0.95 w. p. c. and not at 1.00
w. p. c. as presumed by one of the speakers in referring to the
last paragraph on page 826. The meaning which this paragraph is
intended to convey is that the actual forced life values of all sizes
of tungsten lamps are corrected mechanically to their equivalent
at 1. 00 w. p. c, and of all carbon lamps to their equivalent at 3.05
w. p. c, by using the recording and computing devices in the
manner described. For example, in the record of the 40 watt
tungsten lamp shown in figure 4, it is seen that the actual life
was 505 hours at 0.947 w. p. c, the equivalent of which is 757
hours at 1.00 w. p. c. This lamp was rated at 1.05 w. p. c. by the
manufacturer and the life specified was 1,000 hours. This is
equivalent to 697 hours at 1.00 w. p. c, and hence the life of the
lamp was 108.6 per cent, of the life required.
TRANSACTIONS
OF THE
Illuminating Engineering Society
Vol. X DECEMBER 30, 1915 NO. 9
EFFECT OF ATMOSPHERIC PRESSURE ON THE
CANDLEPOWER OF VARIOUS FLAMES.*
BY E. B. ROSA, E, C CRITTENDEN AND A. H. TAYLOR.
CONTENTS.
I. Previous Investigations and Purpose of this Work.
II. Apparatus.
III. Measurements on Pentane and Hefner Lamps.
IV. Observations on Gas Flames.
V. Computing and Combining Observations on Gas.
VI. Explanation of Effect of Pressure Changes.
VII. Effect of Water Vapor.
VIII. Effect of Vitiation of the Air.
IX. Bearing of Results on Tests of Gas.
X. Typical Applications to Gas Measurements.
I. PREVIOUS INVESTIGATIONS AND PURPOSE
OF THIS WORK.
It has long been known that the candlepower of flames is
affected by atmospheric pressure. Quantitative observations over
a wide range of pressures were made by Frankland about 1859.1
In more recent years the matter has become of practical im-
portance through attempts to define exactly units of luminous
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, 191 5.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
1 Phil. Trans.. 151, pp. 629-653, 1861.
Proc. Royal Soc, 11, pp. 366-372, 1860-62.
Jour. Ckem. Soc, 15, pp. 16S-196, 1862.
Pogg. Annalen., 115, pp 296-335. 1862.
844 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
intensity based on flame standards. The development of such
standards which were reliable enough to repeat values very pre-
cisely, under given conditions, and the simultaneous development
of electric lamps which were independent of atmospheric condi-
tions, made possible fairly precise determinations of the effect
of pressure.
In most cases these determinations were made by measure-
ments at the prevailing pressure, the variations obtained being
only those arising from the natural changes in barometric
pressure.2
Bunte3 made some attempts to control artificially the pressure
of the air around a Hefner flame, but did not succeed in getting
satisfactory results.
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100
40 50 60 70 80
BAROMETRIC PRESSURE CM. OF MERCURY
Fig. i.— Variation of candlepower of certain flames with barometric pressure.
Butterfield, Haldane and Trotter,4 using a steel cylinder built
for the study of caisson disease, carried out the most extensive
experiments of this kind which had been made up to that time.
Their results on standard pentane and Hefner lamps are shown
in Fig. I.
2 I,iebenthal, E., Zs.f. Instrument., 15, p. 163, 1895;/./. Gas, u. IVasser,. 49, p. 561, 1906.
Paterson, C C, Electrician {London), 53, p. 751, 1904; /. Institution of Elect. Engineer,
ing., 38, p. 271, 1906-07; J. Gas Light., 99, p. 232, 1907: N. P. L., Collected Researches, 3 p.49,
1908.
Rosa and Crittenden, Bureau of Standards Bulletin, 10, p. 562, 1914.
*Jour.f. Gas u. IVasser, p. 310. 1891,
*J. Gas Lighting, 115, p. 228, 1911.
ROSA, CRITTENDEN, TAYLOR '. CANDLEPOWER OF FLAMES 845
In the United States the flame standards are not primary or
fundamental, but are calibrated at the Bureau of Standards by
comparison with electric standards under nearly normal atmos-
pheric pressure. The correction for atmospheric pressure is
therefore small, and although it had never been determined very
accurately, the possible error (due to this uncertainty in the cor-
rection factor) in the normal value of a flame standard was very
slight so long as it was used at or near sea level. When, however,
such a flame standard was employed at higher altitudes, it was
known that the candlepower was considerably less, but we
possessed no reliable data for calculating the candlepower at such
reduced pressures. It hence resulted that when flame lamps are
used as candlepower standards, either for testing the candlepower
of gas as given by open flame burners, or the candlepower of gas
sources such as mantle burners or acetylene flames, the standard
might be 10 per cent, or 20 per cent, over-rated by assuming its
candlepower to be the same as it would be at normal barometric
pressure, and hence the same error would be introduced into the
measurements.
Nothing is more obvious than that the candlepower of a light
source used as a standard should be known under the conditions
of its use, and yet for lack of means of determining the effect of
varying atmospheric pressure, flame standards have been used
very generally at widely varying barometric pressures with values
assigned under normal atmospheric pressure. Moreover, this
variation in candlepower due to variations in pressure was pre-
sumably different for different kinds of lamps and burners, and
yet no experiments had been made accurately enough to determine
correction coefficients satisfactory even for commercial use.
Values of the pressure coefficient for pentane lamps had been
computed from measurements made at varying atmospheric
pressures at the Bureau of Standards, but the natural variations
in the barometer at one place are too small to give reliable re-
sults by this method for pressures differing considerably. It was
first proposed to select two or three test stations at different alti-
tudes and make a considerable series of measurements on a
variety of flame sources at each, and then compute the pressure
coefficient from the results. Since the trouble and expense of
846 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
carrying out such a project under conditions favorable enough to
give results of the required accuracy would be very great, it was
decided to attempt to build an apparatus that would permit the
measurements to be made in our own laboratories with variations
of pressure corresponding to two or three miles range in altitude
above sea level.
Our experience with flame standards had shown that for ac-
curate measurements it is necessary to have an atmosphere free
from drafts or sudden slight variations of pressure, and very
perfect ventilation. At first it appeared doubtful whether we
could maintain the necessary circulation of fresh air in a steel
enclosure and keep the flame free from the vibrations or move-
ments due to slight variations of pressure or drafts so as to make
satisfactory measurements of candlepower. But the success of
the apparatus was greater than we anticipated, and we found that
flames could be burned enclosed for an indefinite period under
conditions of perfect ventilation, and measurements made with
less error due to variations in the flame than when they were
burned as usual in the open room. The apparatus has also been
used to re-determine the humidity coefficient, that is, the effect
upon the candlepower of atmospheric humidity, usually expressed
in terms of liters of water vapor per cubic meter of dry air.
The variation in the candlepower of a gas flame with variation
of atmospheric pressure is due to two separate causes ; first, the
quantity of gas burned is reduced when the pressure is reduced,
5 cu. ft. per hour (for example) giving a mass of gas that is
directly proportional to the pressure. Second, the luminous effi-
ciency of the flame, that is, the quantity of light per unit mass of
gas burned, varies with the pressure. The experiments give the
combined effect of these separate causes, and when the first can
be calculated (as when the volume of gas burned is measured)
the second can be determined by itself.
II. APPARATUS.
For the purpose of controlling the pressure we designed and
built a complete set of apparatus as shown in the accompanying
photograph, and in the sketch, Fig. 2. Referring to the sketch,
tanks A and B are each 3 ft. (0.91 m.) in diameter and 5 ft.
(1.52 m.) high. Tank A has a wooden floor about 1 ft. from the
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Fig. 2a.— Diagram of testing apparatus.
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Fig. 3-— Variation of eandlepower of certain flames with barometric pressure; i— Hefner
lamp; 2— Pentane lamp; 3— No. 7 Bray slit union gas burner.
GAS RATE AT BURNER-CU. FT. PER HR.
Fig. 4. — Variation of efficiency with consumption at various pressures of a Sugg's F
Argand burner.
,
ROSA, CRITTENDEN, TAYLOR : CANDEEPOWER OE FRAMES 847
bottom. This floor has a large number of small holes, which
serve to diffuse the incoming- air and prevent drafts. On one
side is a door 15 in. (38.10 cm.) by 30 in. (76.20 cm.) which can
be made air-tight, when shut, by means of fourteen hinged bolts.
Above the door a shaft enters the tank, and by means of suitable
fittings it is used to adjust the flame height of the lamp under
observation, there being a glass window in the door for this pur-
pose. At a point about 900 from the center of the door is an-
other glass window, through which the light from the lamp under
test shines on the photometer screen. On the side opposite this
window is arranged a cabinet containing an Assman psychrometer
for measurements of humidity. This cabinet is connected at top
and bottom to the tank, so that air can be drawn in at the bottom,
passed over the thermometer bulbs, and back into the tank at the
top of the cabinet. The fan of this psychrometer is driven by an
electric motor. A mercury manometer tube is also connected to
this tank to measure the atmospheric pressure in the tank. About
15 in. from the top of the tank is a wooden partition with a
hole about 16 in. x 25 in. (40.64 x 63.50 cm.) for preventing the
products of combustion from passing back down around the
flame.
Tank B is used as an equalizing tank, to prevent sudden
fluctuations or throbs of pressure. It is joined at top and bottom
with tank A by 3 in. (7.62 cm.) pipes. Near the center it has a
thin rubber diaphragm, to assist in eliminating pressure throbs.
To the top chamber of this tank is connected another steel tank,
14 in. (10.16 cm.) in diameter and 5 ft. (1.52 m.) high, which
serves as a further reservoir between the working tanks and the
air pump. To the bottom chamber of tank B are connected two
air meters in parallel, a calcium chloride drying chamber, and a
tank containing water for saturating the air. Twelve valves are
so arranged that the air may pass through the tanks in any of the
following ways : Room air, through or around the meters ; room
air through the CaCl, drying chamber ; room air through the sat-
urating tank ; room air through the pump, through the meters and
tanks, back out to the room or outer air. The last named ar-
rangement is for use in getting pressures above atmospheric
pressure. The arrows indicate the path of the air when the
pump is being operated as a vacuum pump, and room air is being
848 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
drawn through the meters. The pressure in the tanks and the
rate of air flow are controlled by valves 6 and 7. A Zeiss re-
fractometer, not shown in the sketch, was arranged to take
samples of air from the tank for tests of C02.
III. MEASUREMENTS ON PENTANE AND HEFNER
LAMPS.
In most of this work photometric measurements have been
made against electrical standards, using the substitution method,
the electrical standards being burned in place in the tank, the
voltages of the standard and comparison lamps being measured
by the use of a potentiometer.
When work was begun on the pentane lamp it was necessary
to make preliminary tests to determine the rate of flow of air
through the tanks which would be rapid enough to prevent vitia-
tion of the air, and at the same time not to cause drafts or to
affect the candlepower of the lamp by cooling certain parts of
it. Rates of air flow at- tank pressure from about 450 to 1,100
cu. ft. (12.74 to 31.14 m.3) per hour were tried, and it was found
that there was no measurable effect on the candlepower due to
imperfect ventilation until the rate was reduced below 550 cu. ft.
(15.57 m-3) Per hour. Measurements of this nature were made
at various pressures, results being the same in each case. The
rate finally adopted was from 700 to 800 cu. ft. (19.82 to 22.65
m.3) per hour (at tank pressure). The refractometer indicated
that there was no increase of C02 in samples of air, taken from
near the flame, over that in the outside air.
Each candlepower observation at any pressure was the average
of about 75 or more separate settings of the photometer. After
changing the air pressure in the tanks and adjusting the rate of
air flow, no measurements were made until the pressure had be-
come constant. Candlepower measurements on the pentane lamp
were made at pressures from 463 to 1,072 mm. The results are
plotted in Fig. 3. The average candlepower of the lamp under
normal conditions, as determined by previous measurements in
the open air, was 9.78. The curve drawn to represent the aver-
age of observations at various pressures indicated a value of 9.76
candles at normal pressure and water vapor. Hence it is evident
that the unusual conditions of burning did not affect its candle-
ROSA, CRITTENDEN, TAYLOR \ CANDEEPOWER OF FLAMES 849
power at normal pressure. Also, the barometric pressure factor
over the range from 730 to 770 mm., the range obtainable under
natural conditions in this laboratory, was found to be in close
agreement with that which we had obtained when burning the
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Fig- 5-— Variation of efficiency with consumption at various pressures.
lamps in open air in the laboratory, namely, 0.6 per cent, change
in candlepower for 1 cm. change in pressure.
The method of testing the Hefner lamp under various pres-
sures was similar to the above, except that it was not necessary
to regulate the rate of air flow so closely. In this case the deter-
85O TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
mining factor was the maximum allowable rate which would not
disturb the steadiness of the flame. It is interesting to note that
the Hefner flame was much steadier when burning in the tank
than when burning in the open air, and the variations from the
mean value at any pressure were very small, as will be seen by
reference to Fig. 3. This suggests the desirability of using the
Hefner in such a ventilated enclosure when the highest accuracy
is desired.
For both the pentane and the Hefner lamps frequent measure-
ments of water vapor content of the air were made, and observed
results were corrected to a standard value of 8 liters of water
vapor per cubic meter of dry air for the pentane lamp, and 8.8
liters for the Hefner.
IV. OBSERVATIONS ON GAS FLAMES.
In order to reduce measurements on gas flames to a definite
basis, it was first necessary to determine the relative efficiency of
each burner at various rates of gas flow, since it is not always
possible to make the rate exactly 5 cu. ft. (0.14 m.3) per hour.
Such measurements were made at various pressures, and curves
plotted to show the efficiency at any consumption in terms of
the efficiency at a rate of 5 cu. ft. per hour (see Figs. 4 and 5),
and all later observations were reduced to the value which would
have been obtained if the rate had been made exactly 5 cu. ft. per
hour at the pressure and temperature prevailing in the tank.
The three burners tested were the Bray No. 7 Slit Union, the
Von Schwarz No. 8 E. H., and the new Sugg's F Argand. The
Bray burner had its maximum efficiency near 5 cu. ft. per hour
at all pressures, but the rate for maximum efficiency for the other
two burners increased as the air pressure was lowered. In the
case of the argand burner, especially, the corrections made by
the use of these curves were very important. For example, at
500 mm. pressure a variation of 1 per cent, in rate of flow of the
gas would make 2 per cent, change in the efficiency, and there-
fore 3 per cent, change in the observed candlepower; in other
words, the indirect effect in changing the efficiency was twice as
great as the direct effect of having more gas to burn.
As no gas storage tanks were available, it was necessary to
make the observations in such manner as would eliminate any
ROSA, CRITTENDEN, TAYLOR: CANDLEPOWER OE FLAMES 85I
errors due to change of quality of gas during measurement. The
method employed was to make observations at pressures which
were decreased by steps to the lowest value desired, then in-
creased by steps intermediate between the former pressures
The quality of gas usually was sufficiently constant to give very
good agreement between the two series of points thus obtained.
All measurements to determine the effect of barometric pres-
sure on the candlepower of gas flames were made with the gas
rate at the burner as near 5 cu. ft. per hour as could be obtained
without taking excessive care, as this is the customary test con-
dition. Photometric and gas rate measurements were made sim-
ultaneously. The rate of air flow through the tanks was main-
tained at approximately 700 to 800 cu. ft. per hour. Each point
plotted on the curves shown is usually the mean of 75 to 150
separate settings of the photometer, the larger number of read-
ings being taken when the candlepower seemed to be unsteady.
All photometer readings were printed on a sheet by apparatus of
the kind regularly used at the bureau for this purpose, so that a
great many readings could be taken in a short time, with a mini-
mum of prejudice.
V. COMPUTING AND COMBINING OBSERVATIONS
ON GAS.
In each run the observed value was corrected for the variation
of efficiency with consumption, if the gas rate was not exactly
5 cu. ft. per hour. This value was further reduced to constant
mass of gas, vis., 5 cu. ft. at 30 in. (76.20 cm.) and 6o° F. Next
these final corrected candlepower values were plotted against
barometric pressures, and the curve which would best represent
the points obtained in that one run was drawn. As it is not
possible to combine runs from day to day on a candlepower basis,
because of slight changes of quality of gas from day to day, a
certain barometric pressure, well within the range of pressures
used, was chosen as a combination point for the various runs.
For one burner tested the pressure chosen was 650 mm. After
each run had been plotted and the curve drawn, the candlepower
value at 650 mm. was read off from this curve. This candle-
power was then rated as 100 per cent., and all observed candle-
powers of this run were reduced to percentages of this value.
852 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
Each run having been worked up in this manner, all were on a
common basis, and could be combined in a single plot. When
this had been done, and the most probable curve drawn, all ob-
servations were then reduced to a basis of 100 per cent, at 760
mm. The observations, reduced as described above, are plotted
in Fig. 6 and in order to facilitate comparison one of these curves
(No. 3, that for the Bray burner) is also plotted with the pentane
and Hefner lamp data in Fig. 3.
It is to be noted, however, that the standard lamps are operated
at constant flame height, whereas the measurements on the gas
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BAROMETRIC PRESSURE . CI*- OF MERCURY.
Fig. 6. — Variation of candlepower of gas -with barometric pressure— constant mass of gas.
i— Sugg F Argand burner; 2— Von Schwarz No. 8 F- H. burner; 3 — No. 7 Bray burner.
burners are reduced to the basis of constant (mass) consumption.
These are the conditions under which the "candlepower" is cal-
culated in gas tests, and are therefore of most practical im-
portance; but a better comparison of the underlying phenomena
is obtained by plotting, instead of the candlepower for constant
consumption by mass, the actually measured values, which are
for constant consumption by volume. This gives curve 3a, show-
ing a still more rapid decrease in candlepower with decrease in
pressure. Of course a part of this decrease is due to the re-
duction in the mass of gas burned, and for quantitative compari-
ROSA, CRITTENDEN, TAYLOR : CANDEEPOWER OF FLAMES 853
son with the standard lamp curves we should have either the
latter corrected to constant fuel consumption or the gas curves
corrected to constant flame size, which would give a curve lying
between 3 and 3a. The point to be noted is that the open gas
flames fall off in candlepower much more rapidly than the pentane
lamp, which in turn decreases more rapidly than the Hefner with
falling pressure.
VI. EXPLANATION OF EFFECT OF PRESSURE CHANGES.
The reason for the markedly different effects on different
flames is easily found. The light of the flame supposedly comes
from glowing particles of carbon set free in the earlier stages of
the process of combustion. In the later stages the carbon is
oxidized and becomes non-luminous. The amount of light pro-
duced therefore depends on two factors ; first, the number of
particles of glowing carbon in existence at one time, and second,
the average temperature of these particles.
The number of glowing particles depends among other things
upon the average interval between the first and the second stages
of combustion; in other words, on the interval between the time
when the carbon is set free and the time when sufficient oxygen is
supplied to combine with the carbon. In the case of the Bunsen
flame, in which the fuel and the air are already intimately mixed,
this interval is practically non-existent; the carbon is oxidized
before it becomes incandescent and the flame is therefore non-
luminous. At the other extreme is the smoky flame in which the
second stage is never completed, so that some of the carbon
escapes unoxidized. The various types and conditions of
luminous flames come in the intermediate region.
Barometric pressure affects the amount of light produced be-
cause it affects the rate of diffusion of oxygen through the burn-
ing fuel. In general, as the pressure grows less, the diffusion
is more rapid and the "life" of the glowing carbon particles is
reduced. This reduction is, however, partially compensated by
the second factor mentioned, that is, the temperature of the par-
ticles, for the more rapid access of oxygen results in more vig-
orous combustion with a resulting higher temperature, which in
turn causes each particle to emit more light while it does glow.
854 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
If, then, we start with a smoky flame (which has an excess of
carbon) and reduce the pressure, an actual increase in light may-
result. This condition was, in fact, reached in the case of the
Hefner lamp (Fig. 3), although the difficulty of setting the flame
height under this condition is such that not many measurements
were made in this region.
As the pressure is reduced, however, a point is soon reached
where the reduction in the number of particles over-balances the
increase in the light emitted by the individual particle, and from
this point on the reduction in candlepower is more and more
rapid.
It may be assumed that the curve as given for the Hefner lamp
is typical of flames in general, but that our limitations with regard
to pressure are such that for the other flames we get only small
sections of the curve lying far from the maximum, which is near
the pressure that would give a smoky flame. In a general way,
the whiter a flame is the farther it is from the smoking point, and
the more rapidly its candlepower changes with change of pressure.
A few measurements on an acetylene burner, for example, indi-
cated that at a pressure of 20 in. (50.80 cm.) its candlepower was
about 52 per cent, of normal, while the various burners with il-
luminating gas gave 63 to 72 per cent., the pentane lamp 73 per
cent, and the Hefner lamp 86 per cent., this being the order of the
lamps with reference to color also. Even the difference between
the effects on the two types of open flame burner might have
been predicted. The Von Schwarz burner showed a decidedly
higher efficiency than the Bray, indicating that its flame was
nearer the smoking point, and as would be expected from this the
effect of pressure changes is less on this burner.
It may appear that the curve of the argand burner (Fig. 6) is
decidedly different in shape from those of the open flames, but
this burner has a chimney, which so modifies the conditions with
respect to mixing of air and gas that no comparison can be made
with the other burners.
In this connection, however, the curves of Fig. 4, showing the
variation of efficiency with consumption at various pressures, are
of interest. As the pressure is lowered the consumption for
ROSA, CRITTENDEN, TAYLOR : CANDEEPOWER OF FLAMES 855
maximum efficiency is increased, just as it would be by using a
gas requiring less air for its combustion.5
It appears, therefore, that in this type of burner also the effect
of decreased pressure is attributable to a more rapid mixing of
the air through the gas. The chimney, however, has the effect of
making the burner pass from the condition of good aeration to
that of the smoking flame within a relatively small range of
pressure. So we find that at normal pressures, with the gas used
in determining this curve, this burner has already passed the
maximum efficiency (it was in fact on the verge of smoking),
while at the other end of the pressure range it is falling more
rapidly than the open flame. In other words a given range of
pressure gives a larger part of the typical pressure-candlepower
curve for this burner than it does for the open flames.
VII. EFFECT OF WATER VAPOR.
By means of the apparatus described on page 4, it was possible
to vary the water vapor in the air supplied to the tanks over a
range of 15 to 20 liters per cubic meter of air. By making ob-
servations on gas under various weather conditions, a total range
of about 6 to 45 liters was obtained. Similar measurements over
a smaller range were made on an acetylene flame and an Elliott
kerosene lamp. All of these measurements were made at a baro-
metric pressure of 710 mm. The observed points have been
plotted in Fig. 7 in which the curve for the pentane lamp is also
shown for comparison. This curve was determined by a series
of measurements extending over several months, under natural
conditions, and was reported on in previous papers.6 Its ac-
curacy was further verified by measurements in the tanks. An
explanation of the method by which separate observations of
water vapor effect on gas were combined is necessary, since
the whole range was not obtainable at any one time. The
measurements were made in three series of runs, with ranges
of 24.7 to 45, 12.7 to 38.2, and 6.4 to 23.1 liters. The runs of
each series were combined in a manner similar to that described
above for the barometric curves. The combination points for
5 Gilpin F. H., (Proc. Amer. Gas Inst., 9, pp. 379-401, 1914.) gives a similar family of
curves in which the variable condition is the richness of the gas, instead of barometric
pressure.
6 Trans. III. Eng. Soc, 5, pp. 753-778, 1910; and 6, pp. 417-32, 191 1.
Bureau of Standards Bulletin., 10, pp. 391-417, 1913.
2
856 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
runs of each series were 37, 22 and 15 liters respectively, the
values at these points being called 100 per cent, for each series.
The curve representing each series was, to all appearances, a
straight line, and the straight line representing each series was
computed by the method of least squares. As the slopes of the
three lines were not equal, and as it was necessary to combine
these three series on a basis of 100 per cent, candlepower at 8
liters, certain arbitrary points of combination were chosen. The
three series had been taken with such ranges of water vapor that
v
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ER
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LITERS OF WATER VAPOR PER CUBIC METER OF DRY AIR.
Fig. 7.— Variation of certain flames with atmospheric moisture— barometric
pressure, 71 cm.
two adjacent series would overlap, and the combination point in
each case was chosen near the middle of the overlapping section.
These points were 18 and 30 liters. The percentages of the three
series at the various points were as follows :
Per cent. Per cent. Per cent.
Series at 8 i. at 18 I at 30 i
6.4 to 23.1 liters i°3-5 98.4
12.7 to 38.2 liters — 101.4 96.2
24.7 to 45 liters — — 102.8
Hence the percentage values of the first series (basis of ioo
per cent, at 15 liters) were multiplied by , and the other two
ROSA, CRITTENDEN, TAYLOR \ CANDLEPOWER OF FLAMES 857
. IOO 98.4 , , IOO w 98.4 w 96.2 . ,
by X — — — and by X — — — X — — -, respectively.
103.5 101.4 103.5 101.4 102.8
The observations then being on a common basis, they were plotted
and the most probable curve drawn. The points included in
the three groups are distinguished by dots, crosses and circles,
respectively.
The fact that the three groups covering different ranges had
different slopes shows that the decrease due to humidity is not
really linear. The group of points taken at the lowest humidity
gave a slope indicating a decrease of 5.0 per cent, from the normal
candlepower for each per cent, by volume of water vapor in the
air, whereas the pentane lamp decreases 5.7 per cent. Gilpin7
found 6.0 per cent, for an open flame gas burner.
VIII. EFFECT OF VITIATION OF THE AIR.
It was expected that some difficulty would be met in securing
satisfactory ventilation in the tanks, and hence a few preliminary
measurements on the effect of vitiation of the air were made.
These were not carried out fully, because it developed that the
air in the tank could be kept as pure as that in the regular photo-
meter room, so that no corrections on this account were necessary.
The measurements which were made were obtained by closing
up as tightly as possible a small room in which a pentane lamp
and several gas burners were kept burning. Frequent measure-
ments of the candlepower of the pentane lamp were made, while
air from the neighborhood of the lamp was drawn through the
refractometer mentioned above and readings of the latter were
taken at short intervals. These readings (translated into per-
centages of carbon dioxide in the air) and the candlepower of
the lamp were both plotted against the time, smooth curves being
drawn to represent the march of the two quantities. Four such
runs were made and the combined results are shown in Fig. 8.
The points plotted in Fig. 8 were read from the curves described,
and consequently the deviations of these points indicate the degree
of agreement between different runs, and not the precision of
separate candlepower and carbon dioxide measurements.
The curve shows that the degree of vitiation represented by
an increase of 0.1 per cent, in the carbon dioxide content of the
7 Loco citato.
858 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
air caused a reduction of 3.4 per cent, in the candlepovver of the
lamp. As has been pointed out in a previous paper the percentage
of carbon dioxide is not a precise index of the vitiation, since
the important factor is the reduction of the amount of oxygen
in the air, and the relation between this reduction and the increase
in carbon dioxide depends on the proportions of carbon, hydro-
gen and oxygen in the fuel consumed. The present data there-
fore give only an indication of the general magnitude of the ef-
fect of poor ventilation. They are significant, however, in their
relation to the use of flames as primary or fundamental standards,
which involves the derivation of values for electric standards
100
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PERCENTAGE OF CO, IN MR.
Fig. 8.— Effect of vitiation of air on candlepower of pentane lamps.
from the flames. Outdoor air contains about 0.03 per cent, of
carbon dioxide, while in a well-ventilated laboratory this is likely
to run up to 0.06 per cent. This is a small change for most pur-
poses, but it corresponds to a change of 1 per cent, in candle-
power. If therefore we were to attempt to derive from the flame
our fundamental unit, which should be certain to one tenth of 1
per cent., far more elaborate precautions than have ever been
taken with respect to control of the composition of the air would
be necessary in order to avoid uncertainties due to this cause.
IX. BEARING OF RESULTS ON TESTS OF GAS.
It is of course realized that the results of such measurements
as these depend to a considerable extent on the composition of
ROSA, CRITTENDEN, TAYEOR : CANDLEPOWER OF FLAMES 859
the gas. The gas used was a mixture of approximately 30 per
cent, of coal gas and 70 per cent, of water gas, having an open-
flame candlepower under normal conditions of 20 to 23, and an
average heating value in the neighborhood of 630 E. t. u. per
6--;v:-= c ?Pisi.-:-A>ii cc j,<=3cu=t
Fig.'t). — Variation of candlepower of certain flames with barometric pressure: i — Hefner
lamp: 2 — pentane lamp; 3 — Sugg F. Argand gas burner; 4 — Von Schwarz No. 8 E. H.
gas burner; 5 — No. 7 Bray gas burner.
BAFOMrmiC PRC5SURE.INCM5 Of MERCURY
Fig. 10. — Variation of candlepower of gas with barometric pressure,
Sugg Argand burner. (For significance of curves see following page.)
cubic foot. The curves given are intended to show the general
nature and approximate magnitude of the effects and are not to
be considered a basis for exact corrections to be applied in other
cases.
Nevertheless the results are sufficiently significant so that it
86o TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
has appeared worth while to plot various combinations of the
data in such a way as to emphasize their bearing on tests of gas.
Since the data of such tests are commonly expressed in English
units these curves have been plotted with barometric pressures
in inches.
In Fig. 9 are collected the curves already given for the two
flame standards and for the three types of test burners, the values
plotted for the latter being as before corrected to a rate of 5
standard cu. ft. per hour. The significant point in these curves
is the variation in the ratio of gas flames to standard lamp.
IOC
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BAROMETRIC PRESSURE -INCHES OF MERCURY".
Fig. 11.— Variation of candlepower of gas with barometric pressure,
Von Schwarz No. 8 E. H. burner.
In order to bring out more clearly the effect of this variation
we have plotted in Figs. 10, n, and 12 four curves for each type
of burner. In each case curve No. 1 shows the actual candle-
power of the gas flames (as measured by an unvarying standard
such as an electric lamp) burning a constant volume of gas per
hour, that is. 5 cu. ft. per hour at 6o° and prevailing pressure.
Curve No. 2 shows the candlepower corrected to a constant mass
per hour, that is, 5 cu. ft. at 6o° and 30 in. pressure. Curves
3 and 4 in each case show the apparent candlepower which would
be obtained if instead of an unvarying standard a Hefner lamp
ROSA, CRITTENDEN, TAYLOR \ CANDLEPOWER OF FLAMES 86l
or a pentane lamp were used for the measurements without mak-
ing any correction for its departure from normal value, the gas
rate being corrected in the usual way to 5 standard cubic feet per
hour.
90
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2 80
i
£ 70
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2 2
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8AR0METRIC PRESSURE -INCHES OF MERCURY
Fig. 12. — Variation of candlepower of gas with barometric pressure, No. 7 Bray burner.
'0
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Fig- 13— Effect of barometric pressure on "candlepower" of gas as measured with'pen-
tane lamp. 1 — Sugg F (Argand); 2 — Von Schwarz No. 8 E. H. burner; 3— No. 7 Bray
burner.
Since the pentane lamp is generally accepted in the United
States as the most suitable standard for gas tests the rated candle-
powers which would be obtained by using it and correcting gas
862 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
volumes in the customary way are of special interest. Conse-
quently the curves for the different burners showing the results
which would be obtained by tests made with the pentane lamp
as a standard are collected in Fig. 13.
The significance of these curves will perhaps be made more
clear by considering a definite example. Suppose the candle-
power of a given gas, burning at 5 cu. ft. per hour at sea level
(30 in. barometric pressure) in a Bray No. 7 slit union burner is
20.0. If the same gas is burned in the same burner at 5 cu. ft.
per hour at 25 in. pressure, we might expect the candlepower to be
5/6 as great, that is, 16.7, since about 5/(6 as much gas is contained
in the 5 cu. ft. But actually the candlepower is found to be only
14.0, that is, 70 per cent, of 20, as shown in Fig. 12. On the
other hand, a "10-candle" pentane lamp at 25 in. pressure gives
only a little over 9.0 candles. Consequently if we call it 10
candles, the apparent candlepower of the gas flame will be 15.5,
and the customary correction to allow for the fact that only 5/8
of 5 standard cu. ft. of gas are burned gives a rated candlepower
of 18.6. More exact calculations have been plotted in the curves,
and from curve 3 of Fig. 12 we see that at 25 in. (63.50 cm.)
pressure the Bray burner gave 93.5 per cent, of normal values,
or 18.7 candles when the normal was 20.
On the other hand if one had used the Sugg Argand burner the
rated candlepower would have been nearly 6 per cent, above the
normal value, while with the Von Schwarz burner it would have
been 3.5 per cent, below the normal; the actual candlepower,
however, being 15.9 and 14.5 respectively, for gas whose normal
rating would be 20 candles.
It should be noted that by "normal" for each burner is meant
the sea-level value which would be obtained with that particular
type of burner, and similarly the 100 per cent, point on all the
curves is the sea-level value for the particular burner to which
the curve applies. With the gas used in these experiments the
Argand burner gave the highest candlepower, the Von Schwarz
and Bray burners being respectively 2 and 7 per cent, lower.
That is, the same gas gave 20 candles in the Von Schwarz
burner, 20.4 in the argand and 19.0 in the Bray. Different burn-
ers of the two open-flame types selected at random were found
ROSA, CRITTENDEN, TAYLOR : CANDLEPOWER OF FLAMES 863
to give remarkably uniform results, being in this respect de-
cidedly superior to argands.
X. TYPICAL APPLICATIONS TO GAS MEASUREMENTS.
From reports of the Weather Bureau, average values of water
vapor and barometric pressure for five years, from 1904 to 1908
inclusive, for eleven widely separated cities have been obtained.
It is customary to rate a pentane lamp at the candlepower it would
give under normal conditions of 8 liters of water vapor per cubic
meter of dry air and a barometric pressure of 760 millimeters of
mercury. If its candlepower under these conditions were 10.0,
the following table, column 3, would show its average candle-
power for the five years in each of the eleven cities. Assum-
ing a mixed gas of a composition like that tested here, giving a
candlepower of 20 when burned in a Von Schwarz No. 8 E. H.
burner under normal conditions of 8 liters and 30 in. pressure,
the rate being corrected to 5 cu. ft. per hour at 30 in. and 6o° F.,
its actual average candlepower in the various cities is shown in
column 6. Column 7 shows the average values which would have
been obtained if measurements had been made in terms of a
pentane lamp rated as explained above. Column 5 shows the
average candlepower which the consumer would have obtained
for a meter rate of 5 cu. ft. per hour at 6o° F.
TABLE I.— Calculated Rating of Gas at Different Places.
Gas assumed to give 20 candles under normal conditions; all tests supposed
to be made with pentane lamp and Von Schwarz No. 8 E. H. Burner.
Average
Av. actual cp. of gas
Av. water cp. of gas, corrected Av. cp.
vapor at rate to 5 cu. of gas
Average (liters Av. cp. of 5 cu. ft. ft. per hr. as rated
barometric per cubic of pentane per hour at 30 in. with pen-
City pressure
Atlanta 28.84
Boston 29.88
Cheyenne 24.01
Chicago 29.15
Denver 24.73
El Paso 26.19
Helena 25.80
New Orleans 30.00
San Francisco 29.87
Sioux City, Iowa .. 28.80
Washington, D. C. • 29.94
neter)
lamp
at 6o° F.
and 6o°
tane lamp
14-3
9-49
18.3
18.8
19.8
9-9
9.88
19.9
I9.8
20.0
7-3
8.77
13-8
16.9
19-3
10.6
9-75
18.9
19-3
19.8
7-9
8-95
14.4
17-3
19-3
9.2
9.27
15.8
18.0
19.4
6.8
9-3°
15-6
18.0
19-3
19. 1
9-37
19. 1
18.9
20.2
n-3
9-79
19.7
19.6
20.0
9.2
9.78
18.7
19-3
19.7
12.0
9-77
19.7
19.6
20.0
864 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
If a different burner were used the departure from normal
candlepowers would be different. For example, in the case of
Denver, the Sugg F Argand would give for the last three columns
15.6, 18.9 and 21.2 (assuming a gas which under standard condi-
tions would give 20 candles in that burner).
From an inspection of the last column in the above table, it is
readily seen that the candlepower obtained in tests by correcting
results in the ordinary way does not necessarily indicate the
quality of the gas supplied closely enough for a comparison of gas
plant output in different cities. It is still further from an indi-
cation of the average service which the customer is receiving.
If the latter is the purpose of tests of gas candlepower, it would
seem to be a more rational procedure to use a value for the stand-
ard lamp which represents its actual candlepower under the at-
mospheric conditions where and when it is in use. Also, instead
of correcting the volume of gas to its volume at sea level, it would
be better to correct it to the volume at average atmospheric
pressure in the city where tested. Candlepower tests would then
indicate the service rendered much more closely than at present.
The average conditions for any city can be determined quite
closely from the reports of the Weather Bureau.
DISCUSSION.
Mr. F. H. Gilpin: I think it is well to emphasize the fact
of the type of gas on which these experiments were made. If
one takes a burner like the Sugg "F" Argand and burn it, first,
on a water gas and then on a coal gas, totally different results
will be obtained. That particular burner is probably designed
for a little higher consumption than five feet. Atmospheric
humidity will materially affect the efficiency of these burners,
depending on the kind of gas burned in them. In burning a
coal gas, a higher percentage of error will be obtained as the
humidity increases, than with the water gas. Another point in
the measurement of the gas in those tests is this; ordinarily,
in measuring candlepower, the gas is measured by constant
volume and corrected to constant mass. I am interested to know
if any different results would have been obtained in the curves
CANDLEPOWER OF FLAMES 865
if that had been ordinarily done in the test? I notice in the
photograph that the meter was located outside the tank.
Mr. F. E. Cady : It seemed rather interesting to me to notice
that this effect of increasing pressure on the flame candlepower
was in the same direction as that found by Lummer in his
measurement of the effect of pressure on impregnated carbon
arc lamps, and I wondered whether the authors think that the
explanation given of the effect in this case would be similar
and would apply to the effect obtained on the arc lamp.
Dr. E. B. Rosa : I might call attention to one practical ef-
fect of this result: heretofore the Bureau of Standards has
always certified pentane lamps for what we call their normal
candlepower, and that has been used as their actual candlepower
in all altitudes. Even in places no higher above the sea than
Chicago, there is an appreciable difference between the candle-
power and the candlpower at sea level, and of course there are
many cities of considerable size in this country where the al-
titude is several thousand feet and the barometric pressure ef-
fect is correspondingly great. We have never been able to give
with a certificate of the pentane lamp, a certificate of what its
candlepower would be at the place where it was destined to be
used, for the lack of the information now available. We expect
hereafter to give such statements, so that the actual candle-
power will be known, and that will have a very decided effect
on the value obtained by the use of the lamp, if the actual candle-
power at a given place is used instead of its candlepower at
sea level pressure. We have purchased some gas tanks recently
and shall hereafter be able to store the gas and make tests on
different qualities of gas as well as on different types of burners.
Of course, the tests made and reported here as to the effect on
various candlepowers of gas burners, under different conditions,
are not intended as the most important part of this investigation.
We set out to determine it first of all for our standards, but
before making the investigation complete, it will be necessary
to try different kinds of gas to show the variation with the
quality; that we intend to do in the future.
Dr. E. P. Hyde: There is one question I should like to ask
866 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
the authors of this paper, and that is whether they have made
any investigation or drawn any conclusions from the observations
they have made on the relative effect of the vitiation of the air on
the luminous value of gas as burned in the different types of
burners and on the standard pentane and Hefner lamps. In the
photometry of gas every effort is made to have the room ven-
tilated, but some years ago Mr. Bond and myself made some
tests in Philadelphia in one of the laboratories of the United Gas
Improvement Company to endeavor to determine whether the
relative effect of vitiation is the same on gas with the type of
burner that was used and on the standard pentane lamp. I think
that is a point that might be of some practical importance, and
I should like to ask the authors whether they drew any conclu-
sion on that point ?
If there is no further discussion, I will call on Mr. Crittenden
to close the discussion of the paper.
Mr. E. C. Crittenden (In reply) : In regard to Mr. Gilpin's
question as to the method of measuring the gas — he remarked
that the meter was outside the tank, which is true, but the vol-
ume of gas supplied was such, as to make the volume constant at
the pressure in the tank. During some of the tests the meter was
put inside but that caused other troubles. While the meters were
outside it was easy to calculate the amount measured outside that
would become 5 cubic feet inside.
It is recognized, as is stated in the paper, that all of these re-
sults depend markedly on the nature of the gas, and on its rich-
ness. The data given can be applied with certainty only to the
particular type of gas with which the tests have been made. As
to the effect of vitiation, no careful comparison of the effects on
the gas and on pentane lamps was carried out. In a general way,
the effect is very much the same on the two. I am not prepared
to say that it is exactly the same, but it is approximately so. The
data which Dr. Hyde has mentioned obtaining in Philadel-
phia when reduced to the same basis as the curve of Fig. 8 indi-
cate a change of about 3 per cent, in candlepower for 0.1 per
cent, of C02) whereas Fig. 8 shows 3.4 per cent. As stated in
the paper, however, the significant factor is not really the change
in C02 but the reduction of oxygen in the air. Consequently
CANDEEPOWER OF FLAMES 867
when the variation is stated on the basis of C02, the magnitude
of the effect depends on the way in which the CO. is produced.
In regard to Mr. Cady's question— the effects on the arc were
much larger than the effects here obtained, and are caused by the
rise of temperature with pressure. The phenomenon is quite
different in nature from those involved in flames.
868 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
ILLUMINATION AND ONE YEAR'S ACCIDENTS.*
BY R. E. SIMPSON.
Synopsis: The paper presents the results of a study of one year's
industrial accident records, the purpose being to determine the effect of
the lighting conditions in the causation of the accidents. Of the total
number 23.8 per cent, were due either directly or indirectly to the lack
of proper illumination, and of these 51.6 occurred in the four months
having the fewest number of daylight hours. A few typical cases are
given showing how the lighting conditions were responsible for injuries
to workmen. The use of proper reflectors and care in maintaining proper
mounting heights, especially when high efficiency lamps are used, are
essential if accidents are to be prevented by good illumination.
There is a widespread belief prevalent to-day that there are
approximately 500,000 avoidable accidents per year in this coun-
try, and that about one-quarter of this number are caused directly
or indirectly by improper lighting facilities. So far as can be
learned these figures are estimates made by persons who have
had considerable experience in accident-prevention work. There
is little evidence to show that any systematic effort has been made
to point out the relation between light and accident rate. This
is due to the want of statistical data, owing to the enormous
labor and expense involved in obtaining such data. A number
of men interested in good lighting or in accident prevention, or
both, have pointed out the many ways in which the lighting of a
factory may influence the accident rate. In some instances studies
were made of certain industries, notably by Mr. D. R. Wilson,
special inspector in the Factory Inspection Service in Great
Britain, who in 191 1 and 1912 investigated the lighting conditions
in British textile industries and in foundries. In neither one of
his reports are there data to enable one to ascertain the percentage
of accidents due to the inadequate lighting conditions described.
At about the same time, Mr. John Calder presented a paper
before the American Society of Mechanical Engineers, showing
the increase in the number of fatal accidents during that part of
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
SIMPSON : ILLUMINATION AND ONE YEAR'S ACCIDENTS 869
the year when the ordinary factory working hours, 7 a. m. to
6 p. m., extend beyond the daylight period. The curves presented
with his paper showed conclusively that the number of accidents
in December and January was 40 per cent, greater than the
normal number that might reasonably have been expected if there
were the same number of daylight hours in the winter as in the
summer.
The records of workmen's compensation and accident insur-
ance companies offer a fruitful field for the study of accidents,
provided particular attention is given to details in the investiga-
tions. In this respect a few notes on the lighting arrangement
will often explain the cause of an accident. The Travelers Insur-
ance Company is particularly fortunate in having over 200 men
who are specialists in accident-prevention work. A record is
kept of every accident in and about factories, shops, and mills
carrying insurance with the Travelers, and all important ones
are investigated by the inspectors, who ascertain the conditions
that prevailed at the time of the accidents. The reports of these
men form an authoritative library on causation and prevention
of industrial accidents, and among the causes, and the recom-
mendations for the prevention of future accidents, the lighting
question plays an important part.
The main object of this paper is to present the results of a
study of these reports covering a period of one year from Jan-
uary 1 to December 31, 1910. All accidents incident to the use
of automobiles, teams, bicycles, trolley cars, and slippery pave-
ments are omitted, as well as all accidents occurring in and about
coal mines. While there is absolutely no doubt that the darkness
of a coal mine, broken only by the feeble light from the miner's
lamp, is largely responsible for many coal mine accidents, there
are so many other factors bearing on the subject that reliable
conclusions cannot be drawn. It is worthy of note, however, that
the introduction of electricity for haulage purposes has provided
the coal operators with a ready means of lighting the more
important switching points in the mines. The use of steel and
concrete for roof support, and the application of whitewash to the
roof and sides at the turnouts, switching points, and shaft bot-
toms, materially increases the illumination. Good lighting is es-
8/0 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
sential here in order that the motorman may see that the switches
are properly set, and that no standing cars block his way, thus
enabling him to avoid derailments and collisions. The other
employees at these, the busiest parts of the mine, can also per-
form their duties much more efficiently and safely because of the
better illumination.
Excluding these classes of accidents, there still remain more
than 91,000 accidents which occurred in and about industrial
plants; and of this number 23.8 per cent, were due, directly or
indirectly, to the lack of proper illumination. This figure, 23.8
per cent., corresponds very closely to the estimate of 25 per cent,
already mentioned. There is this difference, however, in that
the estimate of 25 per cent, was based on avoidable accidents,
while the 23.8 per cent, obtained from the Travelers Insurance
Company's records embraces both avoidable and unavoidable acci-
dents. It is evident from the records that a large numVr of the
accidents were unavoidable, particularly in those instances where
the lighting condition was a contributory rather than a direct
cause.
A further analysis of the records shows that 10 per cent, of
the total industrial accidents for the year were due primarily to
inadequate illumination, and in the remaining 13.8 per cent, the
lack of proper lighting facilities was a contributory cause. It is
probable that another person in going over these records would
arrive at different percentages of direct and indirect causes of
accidents due to the illumination, but this would simply repre-
sent a difference of opinion in those cases where equally good
arguments might be put forth in favor of one view or the other.
The essential feature of the analysis is the large percentage of
accidents in which the illumination had an important influence.
Under the heading "direct cause" were included all accidents
on stairways, in passageways, or in the shop where it was shown
that there was no light in the immediate vicinity. It is true that
many persons have been injured by falling down stairways that
were well lighted, and, therefore, the illumination could have had
no bearing on the accident. It is likewise true that if none of
the stairways in the country were provided with light, the acci-
dent rate from this cause would be vastly increased.
SIMPSON: ILLUMINATION AND ONE YEAR'S ACCIDENTS 87 1
It may be interesting to cite a few typical cases where insuffi-
cient or improper illumination was a cause of an accident. In a
certain shop having widely spaced lighting units a supporting
column cast a shadow which hid a flat 2-inch bar lying at an angle
across the passageway on the floor. When one of the front
wheels of a truck encountered the bar, the truck axle, swerving
sharply to the right, jerked the handle out of the laborer's hand
and struck the right foot of a workman standing at the side to
let the truck pass. The blow broke one of the small bones in his
foot. The sudden stopping of the truck also caused one of the
heavy pipes on it to roll off, and the truck handle, acting as a
skid, guided the pipe against the workman's left leg, breaking
both bones below the knee. It is evident that neither man saw
the bar of iron on the floor, a fact which is easily understood
when one considers that the floor and the bar were both dark-
colored, and further obliterated by the shadow. It is fair to
assume that had adequate light been provided, one of the work-
men would have seen the bar, and would have removed it instead
of attempting to pull a heavy truck over it.
A paper mill employee, while feeding a conveyor with short
pieces of pulp wood, noticed that the chute at the other end of
the conveyor had become clogged. There was no light at the
chute, nevertheless the man after stopping the conveyor attempted
to clear the way, and while thus engaged a block of wood slipped
out and broke his ankle. There was no occasion for any of the
workmen using this part of the mill unless the conveyor or the
material caused trouble. This, however, was just the time light
was needed and none was provided. The amount of money re-
quired to maintain a unit affording ample illumination at this
point is negligible when compared with the amount of the claim
paid the injured workmen; in fact, such a unit could have been
kept burning all day, and every day for a hundred years, and
still the owner would have realized a handsome profit; and one
employee, at least, would have been saved from injury.
The following two instances represent conditions often seen
in certain industries. In the first one, a man fell into a tank
containing hot water and acid, and was fatally burned. A num-
ber of tanks were placed close together, with narrow walks be-
3
872 TRANSACTIONS OF IEEUMINATING ENGINEERING SOCIETY
tween them at the top. There were no guard rails along these
walks, and no artificial light was provided, even though the pres-
ence of workmen at this point was necessary at odd times of the
day. The accident happened just before quitting time in the
latter part of December. In the other instance the natural light
was not adequate and was supplemented by incandescent lamps.
Both the lamps and the windows had a thick coating of grease
and dirt, so that by no stretch of the imagination could the illum-
ination be called other than very bad. Nor were there any guard-
rails along the walk at the top of the vats containing scalding
water. It is not to be wondered at that a workman made a mis-
step and was scalded to death.
In another case lack of light in the hold of a vessel was, with-
out doubt, responsible for a crushed foot. A workman was piling
pig iron there, in semi-darkness, the open hatch, far above, ad-
mitting so little light that he could not see that the pile was un-
even. While he was still at work the pile toppled over and in-
jured him, as stated. Under exactly similar conditions another
workman could not see that a hook was insecurely caught in a
bale of cotton that was to be hoisted from the hold of a steamer,
and when the hook slipped the falling bale struck the man a
glancing blow, breaking his collar bone. In this instance the dif-
ference of a few inches in the man's position was all the margin
there was between injury and death. In the punch press room
of a certain factory an overhead skylight provided plenty of il-
lumination on bright days, but in the winter months, and es-
pecially on gray, cloudy days, the daylight illumination was so
much reduced as to occasion repeated requests for auxiliary arti-
ficial light; and an injured workman based his claim for damages
on the ground that the employer had failed to provide sufficient
illumination.
Two steam fitters, having finished some work on a temporary
platform 9 ft. above the floor, instructed a laborer to remove all
supplies and tools. The steam fitters had used an extension cord
drop light which they took away with them, thus compelling the
laborer to depend on the reflected light from the units below
him. He failed to see a short piece of steam pipe, which soon
afterward fell on a workman below, fracturing his skull. This
SIMPSON : ILLUMINATION AND ONE YEAR'S ACCIDENTS 873
is the type of accident generally classed under the item of
"struck by falling material." It is probable that if sufficient illum-
ination had been provided, the laborer would have seeri the pipe
and taken it away with the other material, thereby preventing the
accident ; and under the circumstances it is certainly fair to state
that the lack of illumination was a contributory cause.
Two trucks being pushed in opposite directions collided on an
overhead bridge, and both truckmen were injured by material
falling from the trucks. The noise in adjoining shops, in addi-
tion to that caused by the trucks themselves, prevented each truck-
man from hearing the approach of the other. The covered
bridge had side windows, but no other means of providing light,
and as the accident occurred late in the afternoon in January, the
lack of light plus the noise were responsible.
A machine with four saws on one shaft was well guarded, but
the drop light had been so arranged by the operator that one of
the guards cast a deceiving shadow. The man thought he was
placing his hand on the guard, but instead he placed it on the
shadow and was badly injured. This was purely a case of im-
proper lighting, and it points out the hazard in the practise of
permitting a workman to adjust the lighting units to suit his own
convenience, instead of having them placed by a lighting expert
who has studied the safety problem carefully.
A workman using an extension cord light found it necessary
to use both hands, and he, therefore, made a loop of the cord
and hung it about his neck. The worn out insulation of the
lamp cord allowed sufficient arcing to set fire to the man's celluloid
collar, causing extremely painful burns about the neck and head.
In this, as in most other accidents, a great many "ifs" might be
thought of; but none of them can hide the fact that there were
no permanent means of lighting the section of the shop in which
this particular accident occurred.
Finally, there may be mentioned the correlation between a
workman's broken wrist and the rather prosaic escape of two
hogs from a pen. No doubt all would have gone well had not one
of the hogs elected to sleep on the path between two buildings in a
plant. True to his name and nature, the hog obstructed the
whole width of the path, causing the workman to stumble over
874 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
him. There was no means provided to light this pathway, even
though it was the direct route between the buildings, and as such
was in constant use.
There were several cases where inadequate illumination had im-
paired workmen's vision, so that these men were subsequently in-
jured while working under lighting conditions that were ex-
cellent for normal vision. Their claim that their injuries were
due to insufficient lighting was hardly justifiable when applied
to the last working place, but it is certain that the impairment of
their eyesight due to the poor lighting at their previous work-
place had an important bearing on the case.
At the beginning of this investigation an attempt was made to
classify the accidents due to the lighting conditions in greater
detail than "direct" and "indirect," but this soon proved to be
impracticable. If the same proportion had prevailed throughout
the records as was evidenced in the first 5,000 cases investigated,
the lighting accidents on stairways, passageways, and other
seldom-used parts of shops would have had by far the highest
rank. It is very generally recognized by illuminating engineers
that these are just the places that are likely to be slighted in the
original installation, or the maintenance, of factories equipped
and operated by the rule-of -thumb method. If one compares
the number of accidents that occur at these points, bearing in
mind the relatively short time that they are used by a few men,
with the number of accidents occurring in the better lighted shops,
again having in mind the large number of men and the greater
length of time they are subject to the hazards, it is found that
the accident rate in the first-mentioned places is abnormally high.
It is impossible to draw any other conclusion than that the lack
of illumination is largely responsible.
Fig. 1 shows in a diagrammatic form the monthly distribution
of all the industrial accidents reported for the year, and Fig. 2
shows a similar distribution of all the accidents caused by inade-
quate illumination. There is a striking similarity between these
curves and those published by Mr. Calder and other investigators.
From Fig. 2 the fact may be deduced that 51.6 per cent, of
the accidents due to poor illumination occurred in the months
of November, December, January, and February, while 48.4 per
SIMPSON : ILLUMINATION AND ONE YEAR'S ACCIDENTS 875
cent, occurred in the remaining eight months. This indicates that
the likelihood of an accident being caused by poor lighting is
more than twice as great in any one of these four months as in
any one of the remaining eight months.
JULY
AUG
5EPT
OCT
NOV
DEc|jAN
FEB
MAR
APR
MAY JUNE
11000
r \_
10000
\
3000
7000
60O0
5000
-^5=
4OO0
3OO0
Fig. 1.— Showing the seasonal distribution of all industrial accidents for the year.
JULY
AUG | SEPT
OCT
NOV
DEC | JAN
FEB
MAR
APR
MAY
JUNE
1
2000
/
1500
1000
500
^*^
O
Fig. 2.— Showing the seasonal distribution of all industrial accidents caused by
inadequate illumination.
Fig. 3 shows the seasonal distribution of accidents exclusive
of those in which the lighting conditions had an influence. It will
be noted that the increase in the accident rate in the months of
November, December, January, and February is not so pronounced
as in Figs. I and 2. If the lighting condition was the only factor
8/6 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
contributing to the increase in accidents in the winter months,
the curve in Fig. 3 would be practically straight. The similarity
of the three curves raises the question as to whether or not a
greater number of accidents than those shown were due to the
lighting conditions. It is probable that the lack of information
in some of the reports is responsible for a certain number of
accidents attributed to the lighting conditions being overlooked,
but just what this number would be is purely conjectural.
There is another factor which will help to explain the increase
in the accident rate in winter months, and in this the lighting
conditions play an important part, though it is impossible to
obtain any reliable figures. It is partly psychological and partly
JULY
AUG
SEPT
OCT
NOV
DEC
JAN
FEB
MAR
APR
MAV
JUNE
sooo
TOOO
6000
5000
4000
3000
3000
Fig- 3.— Showing the seasonal distribution of all industrial accidents exclusive of those
due to inadequate illumination.
physiological, but may be better understood by referring to it as
the depressing effect of cold and dreary weather on mankind.
It is a well known fact that the members of an exploration party
to the Arctic region are carefully selected not only for their scien-
tific attainments, but also for their physical and temperamental
fitness to withstand the rigors of the weather and the strain of
the long hours of darkness. Notwithstanding this careful selec-
tion, the history of almost every Arctic expedition records the
failure of some of the men under conditions which would have
been easily surmounted if they had prevailed at the beginning of
the expedition. The intense cold and the cheerless outlook brought
about by the lack of comforts craved by the human body, coupled
SIMPSON : ILLUMINATION AND ONE YEAR'S ACCIDENTS 8/7
with the long stretches of darkness, render the men unfit for
their work.
We do not have such extremes of coldness and darkness, nor
such lack of associations or bodily comfort, in our industries.
On the other hand, our workmen are not selected to bear up
under such conditions. Everyone is aware of the depressing
effect of a week of overcast skies with a more or less steady rain-
fall. Substituting cold weather and snow for rain, one can pic-
ture the conditions that prevail in the winter months. Colds and
other ailments are more prevalent in winter, and the afflicted
workmen are less able to guard against injury. Then again there
are many buildings where the window area and arrangement
affords inadequate illumination on cloudy days, even when it is
satisfactory on bright days. This is a condition that is likely to
be overlooked by the inspector if he makes an inspection on a
bright day. It is quite evident that a large number of accidents
might occur under these conditions, and little, if any, thought be
given to the underlying cause.
It is hoped at a later date to make a study of the accidents for
the year 1915, in order to ascertain what influence, if any, the
educational campaign of the Illuminating Engineering Society, the
lamp manufacturers, the insurance companies that have studied
this matter, and others interested in good lighting, has had on
the reduction of accidents. An examination of a few of this
year's reports indicates the trend of the times in that five years
ago general expressions such as "no light" or "insufficient light"
were commonly used in describing the cause of an accident,
whereas at the present time we meet with much more definite
statements, such as "improperly placed lighting units" or "low-
hanging, unshaded lamps." From this one may gather the cheer-
ing information that the workmen are gradually appreciating the
vast difference between light and illumination. It might be
expected that fanciful claims will be made, such as that put forth
by an injured workman to the effect that the actinic rays of the
lighting unit impaired his vision. The lighting unit in question
was a 16-candlepower carbon lamp equipped with a bowl-shaped
aluminum-finished reflector.
A statement has been made to the effect that the introduction
878 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
of the high-efficiency lighting units was the largest single factor
for the increase of accidents in our industries during the period
of artificial lighting. This statement is not to be taken as a con-
demnation of these lighting units, but rather as a protest against
the common method of using them. There are hundreds of small
manufacturing establishments in this country, each one occupy-
ing a single floor or part of one floor in a building. The owners
have had the floor wired and connected for central-station service
or piped for gas service. They have procured incandescent lamps,
gas tips, or mantles, as the case might be, and used them without
proper accessories. Of diffusing glass, reflector equipment,
mounting height, and other fundamentals of good lighting they
either know nothing or care nothing. The workmen adjust the
units so that they can "see," the adjustment generally consisting
in placing the lighting unit close to the work, very often between
the man and the work, and almost always in the direct line of
vision. The carbon lamp or the open-flame gas light contributed
a distinct hazard under these conditions, and the hazard was
greatly increased when the high-efficiency incandescent gas man-
tle and electric lamp were substituted without any other change
being made at the same time.
In some cases the meterman is the only public utility repre-
sentative to visit these small manufacturing concerns, and very
little advice on the lighting conditions is given by these men.
The consulting engineer or lighting expert is seldom, if ever,
called in to give advice on installations where the total connected
lighting load is in the neighborhood of one kilowatt. In the
larger manufacturing plants the lighting bill will bear about the
same proportional relation to overhead expense as it does in the
small shop, although the bill itself will be many times larger.
Economy has generally influenced the management in securing
expert advice on the lighting question with a noticeable improve-
ment in the illumination. This in a measure accounts for the
modern lighting equipment in the large plants and also shows
why they compare so favorably with the small establishments.
A workman may be just as seriously injured in a small shop as
in a large one ; in fact, the accident rate due to the lighting con-
ditions is likely to be higher in the small shop than in the large
SIMPSON : ILLUMINATION AND ONE YEAR'S ACCIDENTS 879
shop doing the same class of work. The accident insurance
companies are assuming risks in the small shops as well as the
large ones, and once a policy is written the premises must be in-
spected periodically. It is the duty of the inspector to prevent
accidents by recommending changes in conditions which tend to
cause injuries to workmen. Since inadequate and improper illum-
ination is recognized as a cause of accidents the insurance com-
pany inspector tries to improve the lighting conditions, and in
this capacity he is probably the most potent factor for improving
the illumination in the small shops.
In the past year the gas-filled tungsten lamp has become an es-
tablished commercial product in a constantly increasing range
of sizes for multiple circuits. The concentrated filament of this
lamp, more nearly approaching a point source, coupled with its
higher intrinsic brilliancy as compared with other tungsten lamps,
makes the use of reflectors absolutely essential. The manu-
facturers are earnestly insistent that users equip these lamps with
proper reflectors, but unfortunately this advice is not always fol-
lowed. In some instances shallow dome-type reflectors were
used with the vacuum-type tungsten lamp, but when the gas-
filled lamps were substituted no change was made with respect to
the reflector equipment or mounting height, even though the
light sources were within the range of vision. Excellent results
in the way of diffusion and distribution can be and have been ob-
tained by the use of the dome-type reflector with the gas-filled
tungsten lamp, but when viewed from the safety standpoint they
should never be used together, unless the mounting height is
such as to preclude any possibility of the lighting source being
within the range of vision. Unless this principle is followed it
is inevitable that the eyesight of the workmen will be impaired,
and with impairment of a workman's eyesight comes a greater
likelihood of injury.
DISCUSSION.
Mr. G. S. Barrows: There are a number of inspection or-
ganizations who make a practise of visiting their clients and ad-
vising them regarding the various hazards and the best methods
of overcoming them. I think from what I have seen of them,
88o TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
however, that on the subject of proper illumination they are
not as well grounded as they might be and I believe it is
a very desirable thing for central station companies to get
in as close touch with such inspection bureaus as possible,
in order to advise them as to the proper steps they should take
to provide adequate illumination. On the eleventh page of this
paper there is a suggestion which I think is a very fruitful one ;
Mr. Simpson says, "In some cases the meter man is the only
public utility representative to visit these small manufacturing
concerns, and very little advice on the lighting conditions is given
by these men." Now what I am going to say applies rather more
to the gas than the electric central station; nearly all gas com-
panies have a maintenance department for taking care of in-
candescent gas lamps ; there is no reason at all why the main-
tenance men should not be given a very thorough training in the
proper placing of lamps. They cannot, of course, become illu-
minating experts but they can be so instructed that they will be
able to recognize hazards ; and while they may not be able to
give the best suggestions for overcoming the hazard, they could
nil in reports regarding the placing of lamps, etc., which
would enable a representative of the illumination department to
inspect the various plants and make suggestions for improving
the lighting conditions. I don't know that that is being done by
any company in this country, but I believe it is something that
the companies ought to begin to do, and I can say that at least
one company is going to take this matter up immediately.
Mr. G. Bertram Regar : The Philadelphia Electric Company
has recently organized a department known as the lighting service
department, practically along the lines as suggested by Mr. Bar-
rows. The headquarters of the department are at the central
office. Here the lighting experts are stationed, and a complete
system of data, instruments, and records of cases investigated
are kept. A representative of the department is stationed at each
of the district offices, whose duty it is to constantly make in-
spections, by day and night, of consumers' installations and advise
the consumers having inefficient installations as to changes to
remedy the defects. The lamp boys are being educated to a
better understanding of illumination and it is their duty when
ILLUMINATION AND ONE YEAR'S ACCIDENTS 88l
making lamp renewals to report poor installations. The instal-
lation men and meter men also have a blank form to notify the
lighting service department. In cases of complaints on bills,
after the meters have been tested and the results explained to the
consumer, the lighting service department is notified, in order that
they may make a thorough inspection for the purpose of possibly
offering suggestions for a more efficient installation. The whole
policy, as can be seen, is to ever improve the service to the
consumer.
Mr. J. L,. Minick : In reading this paper it has been my im-
pression, probably an erroneous one, that Mr. Simpson believes
that the high percentage of accidents during the winter months
can be attributed largely to lighting conditions. This does not
seem to me to be the impression that should be given; not be-
cause we do not wish to prevent accidents so far as it is possible,
but because a study of the curves shown in the paper indicates
that there will be a greater number of accidents during the winter
months regardless of lighting or any other condition.
Mr. R. E. Simpson (In reply) : The two concrete cases cited
by Mr. Barrows emphasize the importance of not depending too
much on the ideas of the workmen on the lighting question, and
in particular on the location of local lamps. In almost every
shop may be found some workmen who can tell just where they
want a lighting unit to be placed, and it will be found that their
ideas conform to illuminating engineering principles. We must
not lose sight of the fact that this class of workmen is in the
minority. There were thousands of cases noted in the investi-
gation where men were employed on drilling machines and simi-
lar operations, where drop lamps, usually unshaded, were de-
pended on for illumination. The lamps are usually placed close
to the work while the controlling mechanism is above the head.
While watching the work or even when looking up the men often
place a hand in the gears instead of on the controlling wheel.
A crushed hand or finger is very probable under these conditions.
I am sure that all who are interested in good lighting and accident
prevention work will be glad to cooperate in the plan advocated
by Mr. Barrows.
It is to be regretted that definite information on the cost of
882 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
industrial accidents is not available. There are so many varying
factors such as the face or amount of the policy, the seriousness
of the accident, attorney fees, etc., that it is hard to arrive at an
average. The 15-watt lamp burning 100 years would cost only
one half as much as was paid to the injured paper mill employee.
Another man receiving the same kind of injury might receive
twice as much, or only one half as much, depending on the factors
already mentioned.
There was no intention of ascribing the high accident rate in
winter months to poor illumination solely. The curves clearly
indicate this, in that their general outline is the same. These
curves tend to prove that the "number of accidents caused by
poor lighting are twice as high in the winter months as in the
summer months. It is in the winter months that artificial light
must be depended on to a greater extent than in the summer
months. In the latter part of the paper other factors influencing
the accident rate in winter are discussed. Mr. Minick's discus-
sion really opens up the whole subject of accident prevention and
is too broad to be thoroughly treated here.
EVANS: INDUSTRIAL LIGHTING 883
INDUSTRIAL LIGHTING WITH MERCURY- VAPOR
LAMPS.*
BY WILLIAM A. D. EVANS.
Synopsis: In the following paper, the mercury-vapor lamp is treated
as strictly an industrial illuminant and it is intended to give an idea of
its various industrial uses and the practise now in vogue. Considerable
data from actual installations are given which should enable those con-
templating installing lamps to follow out the lines already established.
The variety of industries in which these lamps are used embraces prac-
tically every operation in machine shops, foundries, textiles, printing, glass
manufacturing, motion picture studio lighting, etc. In each of the depart-
ments in which mercury-vapor lamps are used, the lamps have a certain
peculiar adaptation for that class of work ; for instance, metal working
plants, in the making of moulds; the grinding and polishing departments,
and in the body finishing and varnishing departments of wood-working
plants, where slight flaws, scratches, blemishes, etc., are easily detected. In
machine work there is very little reflection from bright and shiny parts ;
in the testing department for engines and in foundries, the light pene-
trates the atmosphere; in textile manufacturing and in the inspection of
all kinds of finished products, the magnifying quality of the light makes
details easily perceived ; and in motion picture studio work, the softness
of the light, its high actinic value and diffusion and ease on the eye are
especially desirable. Numerous photographs are shown and a bibliography
of articles on lighting with mercury-vapor lamps is given.
INTRODUCTION.
Artificial lighting in interiors may roughly be divided into two
classes, esthetic and industrial; esthetic embracing the lighting
installations where the idea prevails of harmonizing the illumina-
tion with surroundings; and industrial covering the lighting of
manufacturing plants where the prime consideration is to enable
the eye to do its work with the greatest rapidity and least fatigue.
Mercury-vapor lamps on account of the peculiar bluish-green
color of the light and the tubular form of the light source may
be classified as strictly an industrial illuminant.
Among the advantages derived from these characteristics,
which makes the light particularly desirable for industrial lighting,
are visual acuity, low intrinsic brilliancy and natural differences.
The first mercury-vapor lamps for industrial lighting purposes
were installed in the composing room of the old building of the
New York Evening Post during the summer of 1903. Two 200-
watt lamps were placed over the make-up tables. From this
small installation in a printing plant has developed the use of
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
884 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
mercury-vapor lamps for industrial lighting in all of its different
branches, and at the present time one metal working plant alone
is using a total of about 2,500 tube lamps.
Classification of Industries Where Mercury-Vapor Lamps are
in Use. — The industries in which mercury-vapor lamps have been
successfully used are many and varied, and while it has not been
possible to collect data regarding every operation which is carried
on under the lamps, an attempt has been made to gather sufficient
material which will enable anyone contemplating installing lamps
to follow the practise which has been carried out for similar
classes of work. To attempt to classify the entire industrial field
would be far beyond the scope of this paper, and it is only possi-
ble to give a broad classification. The general divisions will be
given below and the lighting of each operation treated separately.
Table I — General classification of industries in which
mercury-vapor lamps are used for illum-
ination.
Metal working plants.
Foundries.
Forge and blacksmith shops.
Machine shops.
Erecting and heavy machine shops.
Woodworking plants.
Varnish and finishing plants.
Textile plants.
Silk mills.
Cotton mills.
Woolen and worsted mills.
Knitting mills.
Embroidery plants.
Newspaper and printing plants.
Paper manufacturing.
Clothing manufacturing.
Power houses.
Glass manufacturing.
Shipping and storage.
Motion picture film manufacturing.
Miscellaneous.
EVANS: INDUSTRIAL LIGHTING 885
In the installations referred to, the lamps used consist of four
different types, the 20-in. (50.8 cm.) type for direct current des-
ignated as the 200-watt lamp (nominally 192.5 watts) and the
50-in. (1.27 m.) lamp for direct current and alternating current,
both designated as 400-watt almps (nominally 385 watts) and
the quartz or high pressure lamp for direct current designated as
a 725-watt lamp.
METAL WORKING PLANTS.
The illumination of metal working plants probably offers the
largest field for the use of mercury- vapor lamps, not only on ac-
count of the size of the industry, but due to the manner in which
marks and imperfections on metal stand out under the light. The
use of mercury-vapor light is found throughout the entire field
from the making of moulds, where slight blemishes in the sand
are perceived, through the different manufacturing processes up
to the final inspection of the finished product.
Foundries. — The lighting of a foundry may roughly be divided
into three different parts; moulding, embracing core making;
casting floor and the finishing operations, embracing tumbling,
chipping and cleaning. For none of these is there a particular
large amount of light necessary. Most foundries are dark holes
at night, and even in the daytime, during the period of pouring
off, it is extremely difficult to see down the floor on account of the
vapor in the atmosphere. It should be borne in mind, however,
that accidents are a very frequent occurrence and too much light
cannot be provided to guard against the dangers of workmen
falling over moulds, kettles and castings, which may happen to
be in the way. Lamps should be placed out of the field of vision
as far as possible.
The following table shows a number of different foundries
varying in size, which are lighted by mercury-vapor lamps with
data relative to the energy consumption.
Moulding Departments.
Total sq. ft.
I 6,680
2 14,170
3 22,225
4 4,920
5 83,500
Watts
per lamp
Watts
per sq. ft.
Height above
floor, Feet
725
0.33
22
400
0.27
15-27
400
O.56
12
400
0.31
15
200-400
0.21
18
886 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Casting Floor.
Watts Watts Height above
Total sq. ft. per lamp per sq. ft. floor, Feet
1 ■ 15,200 725 O.52 22
2 12,400 725 0.23 27
3 24,000 725 0.24 45
4 28,180 725 O.34 22
5 5>ooo 725 0.29 42
6 44,000 400 0.20 27
7 44.500 400 0.55 12
8 16,300 400 0.30 20
9 30,800 400 0.31 23-35
10 6,900 400 0.31 15
11 13,400 400 0.28 16
12 90,500 400 0.34 18
13 12,000 400 0.26 18
14 28,350 200-400 0.29 18
Tumbling, Chipping and Cleaning.
1 25,500 400 0.29 21
2 16,300 400 0.33 13
3 4,400 200 0.32 10
Forge and Smith Shops. — For this class of work where there
is apt to be moving machinery and high machines, the quantity
of illumination should be somewhat greater than in the foundries.
Welding, case-hardening and tempering are included under this
designation. Data on typical installations for this class of work
are given below.
Watts Watts Height
Total sq. ft. per lamp per sq. ft. Feet
i. Forge shop 24,430 725 0.60 33
2. Forge shop 14,000 725 0.31 27
3. Forge shop 26,000 400 0.29 23
4. Forge shop 3,780 400 0.71 15
5. Forge shop 3,000 400 0.77 10
6. Forge shop 13,820 200 0.17 14
7. Flange shop 16,900 725 0.21 30
8. Smith shop 16,800 725 0.35 27
9. Smith shop 61,380 725-400 0.37 24-34
10. Welding 11,700 400 0.39 14
11. Welding 3,424 400 0.24 20
12. Case hardening 2,770 200 0.82 12
13. Tempering 1,200 400 1.28 9
Machine Shops. — Machine shops may be roughly denned as
all shops where metal is worked with the purpose of reducing
or altering the shape by means of cutting away a certain portion
EVANS: INDUSTRIAL LIGHTING
887
of the material. This will embrace the use of lathes, shapers,
millers, planers, drill presses, automatic machines, punch presses
and so forth. Closely allied to this class of work is the as-
sembling or erecting of the finished pieces, and the inspection of
the parts and final product. There are other operations which
are so closely related to machine shop work that they are in-
cluded under this heading.
The machine shops listed below are all lighted entirely by the
use of mercury-vapor lamps without any individual lamps of the
machines, except in very few cases where it is necessary to bore
inside of castings or some such similar work, which would necessi-
tate the use of individual lamps even with the best daylight. Due
to the low intrinsic brilliancy and the absence of bright spots with
the tube lamps, the reflection from bright metal parts is kept at a
minimum.
Machine Work With Small Tools.
Total
Class of work sq. ft.
Watts
per
lamp
Watts
per
sq. ft.
Height
Feet
I
Miscel. small tools • • 22,800
400
O.66
II
Gear cutting
2
< t
• ii
• 25,240
400
O.62
14
Auto parts
3
(i
1 11
• 11,400
400
1. 12
30
Gen. mach. wk.
4
"
1 1 1
. 4,800
400
O.92
12
11
5
< i
1 11
• 2,190
400
0.95
12
"
6
"
« 11
• 5.840
400
0.73
12
Ball bearings
7
* •<
• ii
• 54,650
400
O.52
13
Auto engines
S
"
' . "
• 30.950
400
O.92
13
Auto parts
6
11
• 11
. 14,880
400
O.63
22-28
Breech mechanism
10
"
ii
. 12,180
400
0.95
IO
Revolver parts
11
"
1 11
• 38,980
200-400
O.60
14
Air brake parts
12
11
1 1 1
. 10,800
400-200
0.50
12
Auto parts
13
11
• ii
• 8,736
200
O.88
9
Gun parts
14
■1
1 ii
. 20,520
200
O.68
9
1 1
15
11
• 11
• 7.760
200
O.89
9
11
16
"
1 1 1
• 5.750
200
O.80
9
1 1
17
"
• 11
• 5.175
200
0 75
9
*'
iS
"
• 11
. 14,700
200
0.55
10
Auto parts
19
"
1 ii
■• 5,400
20O
0.57
10
"
20
"
« ii
. 7,800
200
1. 18
14
Torpedo mfg.
21
Tool
room
• 11,760
200
O.92
11-14
22
1 (
" 2,500
400
O.80
12
23
• 1
6,75o
400
O.80
14
24
II
3.240
400-200
O.7I
12
25
Drill
4
pre*
• 1,790
200
O.65
12
Auto parts
TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Machine Work With Small Tools.— {Continued.)
Watts
per
lamp
400
400
400
400
400
20O
200
400
400
Total
Class of work sq. ft.
26. Milling machines . . . 12,220
27. " " small 12,220
28. Lathes 12,220
29.
30.
3i-
32.
33.
Watts
per
sq. ft.
i-i5
1.18
0.79
1. 12
1.22
0.81
c-75
1. 00
1.28
Height
Feet
IO
IO
IO
IO
IO
8
8
12
10
Reamers 12,220
Model making 12,220
Screw machines 12,390
5,188
" " 11,200
34. Saw finishing 900
* A night photograph of this installation is shown in Fig. 1.
The above machine shops are all those where only small tools
are employed. Where large engine lathes, boring machines and
similar tools are used for working on heavy castings or material
which generally necessitates the use of an overhead travelling
crane, the lamps are usually placed above the cranes or under the
crane rails. These shops are designated as heavy machine shops
and the following data relates to them.
Heavy Machine Work.
Watts
per Height
sq. ft. Feet
0.18 40 Structural steel
0-65 5° Shrapnel mfg.
0.52
0.62
Watts
per
lamp
5
6
7
S
9
10
11
12
13
14
'5
16
725
725
725
725
Total
Class of work sq. ft.
Heavy machine work 300,000
23.35o
28,000
69,600
14,900 725 0.39
14,500 725 0.40
8,250 725 0.35
6,980 725 0.52
Large lathes 14,335 725 0.71
29,400 400 0.59
19,700 400 0.64
11,250 400 0.57
45,780 400 0.48
22,800 400 0.44
17,860 200 0.63
11,400 200 0.44
Heavy machine work
40
50
45
30-48
18
18
18
25
35
12
12
24
20-50
25
23
14
Torpedo mfg.
Eng. mfg.
Shrapnel mfg.
11
Car Wheels
Large gun mfg.
Loco bldg
Punch Presses.— Punch press lighting requires lighting some-
what different from the ordinary machine shop as it is necessary
for the light to shine in and around the dies and to a certain extent
the light will be blocked off by the frame of the press. Moreover,
extreme care must be taken not to have dazzling light sources in
EVANS: INDUSTRIAL LIGHTING 889
the field of vision, for if the eye happens to be momentarily
blinded, it may mean the loss of a finger for the operator. While
the following table gives data for typical lighting of punch press
rooms, however, each installation should be treated separately
and the lamp located with reference to the machines.
Watts Watts Heigbt
Class of work Total sq. ft. per lamp per sq. ft. Feet
1. Pressroom 8,750 400 0.78 12
2- " n,750 400 0.55 12
3- " 18,400 400 0.76 36
Grinding and Polishing. — Another operation which is somewhat
distinctive from regular machining is that of grinding, polishing
or buffing. Extremely good illumination is necessary for these,
as slight flaws and scratches must be detected easily and rapidly
by the men while working.
Watts Watts
Total per per Height
Class of work sq. ft. lamp sq. ft. Feet
i. Grinding 49,980 200 0.26 14 Rim grinding
2. " 1,230 200 0.63 12 Auto parts
3. Polishing 1,510 400 0.80 12 Plated silver
4. " 8,310 400 0.72 14 Revolver parts
5. " 2,090 200 0.74 9 Gun parts
6. " 1,280 200 1.20 12 Engine valves
Boiler, Tank and Plate Shops. — Another class of large shops is
embraced under the classification of boiler, tank and plate shops
where large pieces of sheet metal are worked up for use. This
class of shops as a rule requires very little general lighting as a
good part of the work is carried on inside of the boilers and
tanks, and local lighting is necessary.
Watts Watts Height
Class of work Total sq. ft. per lamp per sq. ft. Feet
1. Boiler shop 30,624 725 0.24 45
2. Boiler shop 26,400 725 0.41 36
3. Boiler shop 12,220 400 0.50 20
4. Tank shop 18,000 725 0.28 35
5. Tank shop 18,000 400 0.34 18
6. Tank shop 6,000 400 0.33 24
7. Tank shop 12,000 400 0.40 20
8. Plate shop 46,900 400 0.15 28
Assembling and Erecting. — The final operations in most metal
working plants is the assembling or erecting of the finished parts.
Here the lighting is apt to vary between wide limits depending
upon the nature of the product. The following data give in-
89O TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
formation relative to assembling of parts in different industries.
Watts Watts Height
Class of work Total sq. ft. per lamp per sq. ft. Feet
1. Asmblg. revolver parts 12,220 400 0.75 12
2. Asmblg. auto parts 6,192 200-400 0.81 12
3. Asmblg. automobiles... 11,566 200-400 0.59 12
4. Asmblg. locks 3,264 200 0.94 10
5. Asmblg. gun parts 6,180 200 0.88 9
6. Erectg. locomotives* . . . 30,625 725 0.28 45
7. Erectg. locomotives 30,400 725 0.29 51
8. Erectg. cars 117,000 400 0.30 20-29
9. Erectg. cars 24,000 400 0.40 25-37
* A night photograph of this installation is shown in Fig. 2.
Testing Departments. — With certain machinery it is absolutely
essential that it be thoroughly tested under service conditions and
in numerous cases 24 hours or longer tests are run, necessitating
as good lighting at night as during the day. In testing auto-
mobile engines, particularly this condition occurs and due to the
large amount of fumes and smoke in the atmosphere, the mercury
vapor lamps have proven particularly desirable on account of the
penetrating power of the green light. Good illumination is very
important as it is often necessary to adjust the carburetors,
magnetos, etc.
Watts Watts Height
Class of work Total sq. ft. per lamp per sq. ft. Feet
1. Testing large machines 7,840 725 0.65 25
2. Auto engine test* 12,750 400 0.41 14
3. Auto engine test 19,200 400 0.75 12
* A night photograph of this installation is shown in Fig. 3.
Inspection Departments. — Inspecting might be termed the most
important operation in the entire shop as every part that passes an
inspection and proves defective in the hands of a customer, gives
the manufacturer a bad reputation. The value of good illumin-
ation in this department cannot be too strongly dwelt upon.
Watts Watts Height
Class of work Total sq. ft. per lamp per sq. ft. Feet
1. Inspectg. revolver parts 6,110 400 0.75 12
2. Silverware inspection. . . 3,400 400 0.82 12
3. Inspectg. auto parts 1,230 200 0.63 10
4. Inspectg. browning 6,550 200 0.94 10
5. Inspectg. gun parts 12,390 200 0.88 9
WOODWORKING PLANTS.
The lighting of woodworking plants is similar to that of
machine shops, inasmuch as the machines must be adequately
EVANS: INDUSTRIAL, LIGHTING
891
illuminated to prevent accidents,
marks on the material. In most
stands out particularly clear under
vapor lamp.
and it is necessary to see the
cases the grain of the wood
the green color of the mercury-
Total
Class of work sq. ft.
i. Planning mill 30,000
2. " 7.000
3. Carpenter shop • • • 3,640
4. Woodworking shop 3,000
5. Carpenter shop • • • 9,000
6. " 12,390
7. Woodworking 6,795
8. " 4,807
9. Carpenter shop • • • 5,600
10. " 5,400
11. Woodworking 6,550
12. " 7,775
Watts
per
lamp
400
400
400
400-200
400-200
400-200
200
200
200
200
200
200
Watts
per
sq. ft.
0.28
0.35
O.69
I.28
0.39
O.56
0.9I
0.96
O.83
O.71
O.94
O.50
Height
Feet
20
17
12
8
15
15
10
10
10
9
10
10
Car parts
Genl. carpenter wk.
Carriage bodies
Rough carptr. work
Genl. carpenter wk.
Gun stocks
" finishing
Box making
<t
Stock inspection
Auto bodies
VARNISHING AND BODY FINISHING SHOPS.
Closely akin to woodworking shops are the varnish shops where
the finish is placed on a great many articles. Under the same
heading is included "Body Finishing" which embraces the painting
and finishing of automobile bodies. This latter is an extremely
important item in the automobile business, as the finish on the car
is the first point to strike the average purchaser. This work is
generally done in a long narrow room with windows on one side,
and the dark rooms on the other. The room is kept closed
throughout the process in order to keep out insects and the
temperature is maintained at a constant point. When working
in daylight it is necessary to turn the bodies, after rubbing down,
to obtain light on the opposite side. This, however, has been
obviated by the use of two rows of mercury-vapor lamps with
angle reflectors, throwing light on both sides of the body and
permitting the work to be done in a great deal less time.
I.
Class of work
Total
sq. ft.
•• 3,756
Watts
per
lamp
200
Watts
per
sq. ft.
O.82
Height
Feet
10 Gun stocks
2.
ii
3.IOO
200
0.75
10 "
3-
4-
11
.. 4,400
2,800
400
400
2.28
2.86
%yz Auto
8K
* A night photograph of this installation is shown in Fig. 4.
892 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
TEXTILE MANUFACTURING.
The lighting of textile plants varies somewhat from that of
machine shop lighting. In almost all cases the machines are en-
tirely automatic and the necessity for seeing generally occurs
when a thread breaks which automatically stops the machine.
Until this thread is repaired that portion of the work is at a
standstill and every second saved in quick repairs means just so
much more output. As the threads in silk work are as fine as one
two-thousandth of an inch, not only is a large amount of light
necessary, but also a light with high visual acuity.
Silk Mills. — The first operation in silk is what is known as
"throwing," which is simply twisting and doubling the threads
over and over again to work them up to the required thickness.
Winding and spinning are also a similar operation, and the fol-
lowing data will cover all of these operations.
Preliminary Operations.
Total Watts Watts Height
Class of work sq. ft. per lamp per sq. ft. Feet
1. Reeling 2,091 400 0.95 9
2. Reeling 4,400 400 1.40 10
3. Spinning 4,185 400 1.00 12
4. Winding 16,200 400 0.50 12
5. Spinning 7,040 400 0.80 12
6. Spinning 10,032 400 1.47 10
7. Spinning 3,000 400 1.02 12
8. Spinning 28,020 400 0.73 10
9. Winding 6,790 400 0.69 12
10. Winding 3,000 400 0.77 12
11. Doubling 4,680 400 0.82 10
12. Winding 20,448 400 0.57 10
13. Reeling 2,150 200 0.54 8
14. Reeling 840 200 0.69 10
15. Spinning 6,465 200 0.48 9
16. Winding 6,220 200 0.69 9
17. Twisting 8,515 200 0.59 9
18. Winding 1,680 200 0.69 10
19. Spinning 3,400 200 1.02 10
20. Winding 2,520 200 0.69 10
Warping and Quill Winding. — After the silk has been worked
up to the proper thickness and twisted, a portion of it is sent to
the warping department and the balance to the quilling depart-
ment.
EVANS: INDUSTRIAL LIGHTING §93
In the warping operation, the silk is unwound from small
spools onto a large drum or beam, from which it is rewound on
the warp and placed in the loom. The balance of the silk is
wound up into small bobbins which are placed in the shuttles of
the loom.
Good illumination is even more necessary for these processes
than for the throwing operations.
Watts Watts Height
Class of work Total sq. ft. per lamp per sq. ft. Feet
1. Warping 10,780 400 I.H 12
2. Warping 10,906 400 1.16 12
3. Warping 2,940 200 0.53 10
4. Warping 7,ioo 400 1.08 10
5. Quill winding 2,020 400 l£l 10
Entering. — When the warp is finished, it is necessary to thread
it through reeds of the harness before the warp can be placed on
the loom. Automatic machines are in use for this work, but a
great deal of it is done by hand and requires a high degree of
illumination.
Watts Watts Height
Class of work Total sq. ft. per lamp per sq. ft. Feet
I. Entering 2,800 400 1.65 12
Weaving. — The main operation in silk is weaving, as this pro-
duces the goods in the final form. Broad silk looms are generally
lighted by using one 400 or 200-watt mercury-vapor lamp to
every four looms, while for ribbon looms one or two 200-watt
lamps are used per loom.
Watts Watts Height
Class of work Total sq. ft. per lamp per sq. ft. Feet
1. Broad silk 11,800 400 1.00 14
2. Broad silk 7.620 400 1-47 12
3. Broad silk 11,508 400 1.27 11
4. Broad silk* 10,780 400 1.21 n
5. Broad silk 10,906 400 1.27 «
6. Broad silk 10,045 400 1.30 II
7. Broad silk 8,890 400 1.37 10
8. Broad silk 29,295 400-200 1.18 14
9. Broad silk 6,000 400-200 1.15 8
10. Broad silk 11,508 400-200 1.6 n
11. Broad silk 7,285 400-200 0.73 10
12. Broad silk 6,340 200 0.55 10
13. Ribbon looms 750 200 1.54 9
14. Ribbon looms 4,800 200-400 0.84 12
* A night photograph of this installation is shown in Fig. 5-
894 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Picking and Inspecting. — After the silk comes from the loom,
it is carefully gone over and picked, which consists of removing
the knots and loose ends and the detection of other flaws which
may have occurred through the carelessness of the weaver.
Watts Watts Height
Class of work Total sq. ft. per lamp per sq. ft. Feet
i. Picking 2,800 400 1.65 12
2. Picking 340 200 1.39 10
Cotton. — The lighting of cotton mills in the arrangement of
lamps is somewhat similar to that of silk, with the exception that
due to the greater thickness of the threads, less light is needed.
Preliminary Operations. — The preliminary operations consist-
ing of lapping, carding, drawing, spooling and spinning are some-
what along the line of the throwing operation in silk manufactur-
ing, the purpose being to prepare the cotton for the loom.
Watts Watts Height
Class of work Total sq. ft. per lamp per sq. ft. Feet
i. Carding 600 200 0.23 10
2. Ring spinning 3,330 200 0.47 10
3. Ring spinning 12,000 200-400 0.68 12
4. Twisting 15,170 200-400 0.68 12
5. Winding 3,660 200-400 0.58 10
6. Warping* 1,500 200 0.64 12
7. Beaming 1,760 200 0.44 12
* A night photograph of this installation is shown in Fig. 6.
Weaving. — In cotton weaving the looms are generaly lighted
by one 400-watt mercury-vapor lamp to approximately every 14
looms or one 200-watt lamp to about every eight looms, depending
somewhat on the arrangement and size of the looms.
Watts Watts Height
Class of work Total sq. ft. per lamp per sq. ft. Feet
1. Weaving (coarse goods) 25,200 200-400 0.52 15
2. Weaving (coarse goods) 26,000 200 0.37 12
3. Weaving (coarse goods) 21,573 200 0.45 10
4. Weaving 36,570 400 0.74 12
5. Weaving 4,580 200 0.78 gy2
6. Weaving 21,000 400 0.66 14
Finishing. — The finishing operation in cotton consists practi-
cally of cleaning the goods, and is the final preparation for the
market.
Watts Watts Height
Class of work Total sq. ft. per lamp per sq. ft. Feet
i. Finishing 6,080 400 0.64 12
"frq H
Fig. i. -A machine shop illuminated by mercury-vapor lamps.
Fig. 2.-I<ocomotive shop illuminated by mercury-vapor lamps.
Fig. 3.- Automobile test shop illuminated by mereury-vapor lamps.
Fig. 4.— Automobile body finishing department illuminated by mercury-vapor lamps
n
Fig. 5._Silk looms illuminated by mercury-vapor lamps.
Fig. 6.— Cotton warp
department illuminated by mercury-vapor lamps.
Fig. y.-A roving department illuminated by mercury-vapor lamps
Fig. S.-Paper machine room illuminated by mercury-vapor lamps.
eqt
Fig. 9 _A power plant illuminated by mercury-vapor lamps.
Fig. io
.-A plate glass inspection department illuminated by mercury-vapor lamps.
Fig. ii.— Craneway illuminated by mercury-vapor lamps.
Fig. 12.— Interior of a moving picture studio.
EVANS: INDUSTRIAL UGHTING
895
Woolen and Worsted. — The preliminary operations in woolens
and worsted consist in scouring the wool to remove the grease,
then carding, combing, spinning and so forth in preparation for
the looms, simlar to other textile operations.
Watts Watts Height
Class of work Total sq. ft. per lamp per sq. ft. Feet
1. Carding and roving*... 26,000 400 0.30 14
2. Carding 6,000 200 0.23 10
3. Mule spinning 5,400 400 0.57 10
4. Winding 2,000 200 0.58 10
5. Spinning 6,600 200 0.30 10
6. Spinning 13,728 200-400 0.53 12
7. Winding 6,500 400 0.94 10
8. Spinning 26,000 400 0.30 14
9. Winding 26,000 400 0.30 14
* A night photograph of this installation is shown in Fig. 7.
Weaving. — In woolen and worsted weaving, the amount of
light necessary and the arrangement is very similar to that in
cotton mills.
Total Watts Watts Height
Class of work sq. ft. per lamp per sq. ft. Feet
1. Weaving 3,75° 4°o 1.13 10 Special goods
2. " 60,000 200 0.64 12
3. " 58,880 200 0.78 9
4. *' 58,880 200 0.71 9
Finishing. — The finishing operation is similar to cotton,, though
somewhat more exacting.
Watts Watts Height
Class of work Total sq. ft. per lamp per sq. ft. Feet
1. Finishing 2,670 200 0.43 10
2. " 2,375 200 0.57 10
3. " 6,600 200 0.35 10
Knitting Mills. — In knitting, the preliminary operations are
similar to those in woolen manufacturing and the data given
above will cover these. After the wool is wound on the bobbins,
it is placed in the knitting machines, and worked up into the de-
sired form.
Watts Watts Height
Class of work Total sq. ft per lamp per sq. ft. Feet
1. Knitting machines 6,500 400 0.94 10
2. *' 4,600 200 0.67 10
3. " 15,000 200 0.56 11
Watts
Watts
Height
per lamp
per sq. ft.
Feet
400
1-33
IO
400
0.94
IO
200
0.43
12
896 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
Stitching Department. — After the goods are taken off the ma-
chines, it is necessary to inspect carefully and sew up the defects.
This is done in the stitching departments.
Class of work Total sq. ft.
i. Stitching machine 5,200
2. Stitching machine 6,500
3. Cutting room 4,5°o
Embroidery Plants. — Embroidery machines can be satisfac-
torily lighted by providing sufficient general illumination to ade-
quately light all parts. The machines are about 30 to 40 feet
(9.14 to 12.19 m.) long and lamps are generally placed directly
over them.
The working out of the patterns is accomplished by means of
a pantagraph. On most machines this is guided by hand, though
in some large plants it is operated automatically.
Watts Watts Height
Class of work Total sq. ft. per lamp per sq. ft. Feet
1. Automatic machine 19,200 400 0.95 14
2. Hand machines 2,400 200 2.00 10
3. Hand machines 2,750 200 0.98 9
NEWSPAPER AND PRINTING PLANTS.
The illumination of newspaper and printing plants covers the
lighting of composing room, stereotype, press and mailing rooms,
all of which will be treated separately.
Composing Rooms. — In a number of composing rooms, the
make-up tables are equipped with inverted V-shaped racks placed
over the tables, and 200-watt mercury-vapor lamps are placed in
under these racks.
For other tables and banks, lamps are hung directly from the
ceiling, and provide general illumination throughout the room.
Linotype machines are lighted by overhead lamps to cover the re-
pairs to the mechanism, but small individual lamps must be placed
on each machine to light the slugs.
EVANS: INDUSTRIAL UGHTING
897
Class of work
Newspaper composing
Printing plant
1.
2.
3-
4-
5-
6.
7. Newspaper composing
8.
9-
10. Printing plant
11. Newspaper composing
12.
13.
14. Linotype machines • • .
Total
sq. ft.
2,515
6,075
9,400
3,120
12,400
6,085
6,300
480
3.430
I,2l8
1,200
1,480
3,500
2,205
Watts
Watts
per
per
Height
lamp
sq. ft.
Feet
400
2-3
12
.400
I-5I
12
200-400
0.72
14
Incl. linotypes
200-400
I.84
IO
200-400
I.92
9
200-400
i-45
10
200
1.47
8
200
3-2
6
Rack lighting
20O
2.4
8-12
200
1.58
9
200
i-55
11
200
1.70
10
200
1.70
10
400
0.70
12
Supplemented by
individual lamps
on machines.
Stereotype Room. — After the forms are made up in the com-
posing room, impressions are made of them on the matrix, and
this is taken to the stereotype room where the cylinders are cast
from them to go on the presses. This lighting is somewhat
similar to that of machine shop lighting, as the plates also have
to be trimmed and cut to size.
Class of work
Total sq. ft.
Watts
per lamp
Watts
per sq. ft.
Heigh
Feet
I.
400
I.03
12
2.
(i
I,000
400
O.77
IO
3-
4-
11
11
2,4IO
880
200
200
O.48
O.44
IO
16
Press Rooms. — Press rooms have been lighted either by general
illumination or by placing lamps directly on the presses in news-
paper work, or by a combination of the two methods.
Class of work
i. Newspaper presses
2.
3-
4-
5-
Magazine presses . .
Newspaper presses
6.
7-
8. Job presses
9. Newspaper presses •
10. Small power presses.
11. Hand presses 12,100
12. Paper handling mach
Total
sq. ft.
Watts
per
lamp
Watts
per
sq. ft.
Height
Feet
6,000
400
O.83
14
I,000
400
i-54
15
9,800
400
o.55
15
7,980
400
0.48
IO
4,000
200
1.05
8-15
Some lamps
presses
7,320
200
0.84
8-14
«(
2,875
200
0.94
IO
650
400
1. 19
12
5,150
200-400
0.82
27
7,728
400
1.82
IO
Engraving pr
I2,IOO
400
i-95
IO
"
7,250
200
o.53
9
898 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Mailing Room. — The work in the mailing room consists of
wrapping and addressing papers or magazines and requires a
fairly good general illumination.
Watts Watts Height
Class of work Total sq. ft. per lamp per sq. ft. Feet
i. Mailing department •••• 4,485 400 0.52 12
2. Mailing department 4,180 200 0.46 10
PAPER MANUFACTURING.
Paper manufacturing consists essentially of four operations:
the grinding room where the wood is ground up, the beater room
where the pulp is mixed, the machine room, and for high grade
paper manufacturing, the calendar room, which is equipped with
machines for putting on the finish. Not a great deal of light is
necessary to see these different operations as not many of them
are particularly fine work, but sufficient illumination must be pro-
vided to obviate any possibility of accidents.
Watts Watts Height
Class of work Total sq. ft. per lamp per sq. ft. Feet
1. Grinding room 2,400 400 0.50 20
2. Beater room 9,000 200 0.13 10
3. Machine room* 8,000 200 0.38 10
4. Machine room 4,000 725 0.35 30
5. Machine room 3,040 200 0.63 12
6. Calendar room 5,615 400 0.50 10
* A night photograph of this installation is shown in Fig. 8.
CLOTHING MANUFACTURING.
In clothing manufacturing certain processes have been satis-
factorily lighted by mercury-vapor lamps. A large quantity of
light, however, is necessary to properly see the texture of the
goods, especially in the pressing where one 400-watt lamps is
generally placed over each pressing table.
Watts Watts Height
Class of work Total sq. ft. per lamp per sq. ft. Feet
i. Cutters . ..- 448 400 1.72 10
2. Hand sewing 5,400 400 0.74 10
3. Pressing 4,500 400 1.60 10
4. Pressing 1,650 400 0.95 10
5. Pressing 880 400 2.19 10
6. Pressing 2,445 400 1.64 IX
POWER HOUSE LIGHTING.
Power house lighting covers the illumination of the boiler
rooms and engine and generator rooms. In the boiler rooms gen-
EVANS: INDUSTRIAL, UGHTING
899
eral illumination is provided for the aisles with small individual
lamps placed at the gauge glasses. While in the engine and gen-
erator rooms, individual lamps in some cases are used in and
under the engines. The amount of illumination is generally not
very high.
Watts Watts Height
Class of work Total sq. ft. per lamp per sq. ft. Feet
1. Boiler room 12,985 200 0.60 18
2. Boiler room 8,945 200 0.64 18
3. Boiler room 12,670 200 0.58 16
4. Boiler room 18,000 400 0.17 40
5. Boiler room 7,065 400 0.27 20
Engine and Generator Rooms.
1. Turbine room 20,000 725 0.25 46
2. Turbine room 27,000 725 0.24 85
3. Turbine room 10,500 725 0.2 1 81
4. Sub-station 4,200 400 0.64 25
5. Turbine room 13,980 400 0.33 40
6. Turbine room* 27,000 400 0.17 18
7. Engine room 10,470 400 0.22 32
8. Turbine room 25,345 200-400 0.49 18-45
9. Engine room 8,100 200 0.24 14
10. Engine room 13,200 400 0.58 30-75
* A night photograph of this installation is shown in Fig. 9.
GLASS MANUFACTURING.
The operations in glass manufacturing which have been suc-
cessfully lighted by mercury-vapor lamps are all grades of in-
spection, the grinding and polishing and similar operations of plate
glass, machine cutting and engraving of cut glass. The latter and
inspection requires extremely good illumination.
Watts Watts Height
Class of work Total sq. ft. per lamp per sq. ft. Feet
1. Lehr inspection 384 400 2.00 12
2. Polishing and grinding 11,890 400 0.71 22
3. Polishing and grinding 42,000 725 0.38 36
4. Stripping 11,890 400 0.71 15
5. Laying 7,680 400 1.10 15
6. Final inspection* 3,000 400 1.28 10
7. Machine cutting 10,300 400 0.85 12
8. Engraving 600 400 5.00 12
* A night photograph of this installation is shown in Fig. 10.
SHIPPING AND STORAGE.
Practically all manufacturing plants have shipping and storage
departments, and while in a great many cases where there are high
900 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
bins mercury-vapor lamps on account of the size may not be avail-
able, still in numerous cases they have been successfully used for
storage and for shipping and similar departments.
Class of work Total sq. ft. peTtp pJSfft *&£'
i. Warehouse i4)6oo 200 0.24 10
2. Shipping platform 1,000 200 0.96 8
3. Freight house 76,000 200 0.20 8-10
4. Freight house 14,400 200 0.32 8-10
5. Freight house 9,600 200 0.24 10-12
6. Shipping dept 7,800 400 0.49 12
7. Craneway* 33j6oo 725 0.25 80
* A night photograph of this installation is shown in Fig. n.
MOTION PICTURE STUDIOS.
Whether motion picture studios may be termed industrial plants
is somewhat open to discussion, but it is in the studio that the
first operation in the manufacture of the film is performed,
and as mercury-vapor lamps are extensively used for this class
of work, data regarding them may be of interest.
As far as is known, there are in the United States about 50
studios using artificial light for the taking of motion pictures.
Of these 43 are using mercury-vapor lamps either entirely or in
combination with other systems. Nearly all of them use at least
one or two large arc lamps to obtain special lighting effects. The
data furnished below do not take into account the energy con-
sumed by these arcs.
Watts per
, sq. ft. of floor
IS umber stages Watts per lamp area illuminated Height, Feet
I
2
3
4
5
6
7
8
9
10
4 400 100.0 8-16
1 725-400 65.0 8-10
1 725-400 47.0 8-15
2 4oo 128.0 8-14
2 400 100.0 8-15
1 4oo 83.0 8-12
1 400 99.0 8-13
1 400 104.0 8-13
1 400 89.0 8-12
i-I2
1 400 85.0
* A night photograph of this installation is shown in Fig. 12.
EVANS: INDUSTRIAL LIGHTING 901
MISCELLANEOUS INDUSTRIES.
In addition to the data given in the previous tables, there have
been obtained information relative to the lighting of certain oper-
ations in other industries which are all grouped under the head-
ing of miscellaneous industries.
Illum'd. Watts Watts per Height
Plant Operation sq. ft. per lamp sq. ft. Feet
1. Rubber Rubberizing cloth • • 4,550 200-400 0.46 16
2. Steel Rolling mill 24,000 400 0.20 15
3. Metal fur. Finishing 9,405 4°o 0.49 12
4. Metal boats " 16,900 400 0.36 14
5. Hatmfg. Sizing room 7,240 400 0.64 12
6. Shoemfg. Cutting 870 200-400 3.12 10
7. Copper refg. Electrolytic room •• • 86,400 725 0.18 29
8. Metal plant Electroplating 8,340 200 1.00 11
9. Copper refg. Grind'g and crush'g 4,500 200 0.13 40
10. " Concentrating 8,000 200 0.14 12-16
TI- " Jigs 10,000 200 0.15 18-28
12. Powder mfg. Pressroom 1,200 400 1.00 9^
13. Sugar plants Inspection dept. 200 One for ea insp. 8
14. Ivory plants Sorting dept 200 " sorter 8
CONCLUSIONS.
The data furnished in this paper have been the result of
practically twelve years use of mercury-vapor lamps in the in-
dustrial field. While the figures vary somewhat for the same
class of work, it might be said that this condition depends to a
certain extent on the state of mind of the different plant man-
agers. Some appreciate the fact that up to a certain limit they
cannot have too much light to produce the best results and look
upon good lighting as an asset; whereas others feel that they
wish to get along with as little light as possible, and feel that light
is merely a necessary evil which must be used.
By using the figures given there is no doubt but what the plant
engineer of any concern desirous of using mercury-vapor lamps
will be able to estimate fairly accurately the amount of light that
may be needed for different operations.
In designing a good industrial lighting system, the following
points should be borne in mind. Provide an illumination that will
not dazzle the eyes of the operatives, one with a low intrinsic
brilliancy and with as little glare as possible that will be easy on
the eyes of the operatives and thoroughly diffused, all of which
902 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
will tend to prevent accidents and safeguard the health of those
working under it.
The system of lighting should be installed with the idea of pro-
ducing the greatest quantity of goods of the best quality, in other
words, design the lighting not with the idea of the "proximate"
efficiency of the lighting unit, but with the "ultimate" efficiency of
the plant.
BIBLIOGRAPHY ON ARTICLES DEALING WITH MERCURY-
VAPOR LAMPS FOR INDUSTRIAL LIGHTING.
Allen, F. B.
Important Considerations in Factory Lighting.
Electric. Review, Aug. 2, 191 1.
Bell, Louis.
Chromatic Aberration and Visual Acuity.
Electrical World, May 11, 191 1.
Clover, G. R.
Lighting a Stock Room.
111. Eng., vol. 6, No. 12.
Evans, W. A. D.
Illumination of a Large Foundry.
111. Eng., vol. 5, No. 11
Lighting Problems in the Automobile Industry.
111. Eng., vol. 6, No. 10.
Lighting a Large Power House.
111. Eng., vol. 6, No. 1.
Illuminating a Newspaper Printing Office.
111. Eng., vol. 5, No. 12.
Illumination of a Glass Factory.
Elect. Review, July 10, 1915.
Light as a Factor of Efficiency.
Textile World Record, Nov. and Dec, 19 14.
The Mercury-vapor Quartz Lamp.
Paper presented before I. E. S., Sept. 22, 1913.
Artificial Lighting of Motion Picture Studios.
111. Eng., London, June, 1915.
Fortune, F. R.
Foundry Lighting.
Haviland, F. M.
The Light for the Printer.
Inland Printer, Jan., 1914.
EVANS: INDUSTRIAL LIGHTING 903
Hubbard, A. S.
Lighting an Embroidery Shop.
111. Eng., May, 191 1.
Mercury -vapor Lamps in the Textile Industry.
111. Eng., vol. 3, No. 9.
Illumination of a Cotton Mill.
111. Eng., vol. 5, No. 7.
Cooper Hewitt Lamps in a Silk Mill.
American Silk Journal, May, 1908.
Lighting the Stehli Plant at Lancaster.
American Silk Journal, Sept., 1908.
Hubbard, W. C.
Three Interesting Problems in Industrial Illumination.
111. Eng., vol. 6, No. 2.
Keech, G. C.
Carefully Planned Factory Lighting.
Mfrs. News, Nov. 5, 1914.
Quartz Tube Lamp in Railroad Service.
Before Electric Club of Chicago, Nov. 14, 1912.
Knapp, S. H.
Lighting of Erecting and Heavy Machinery Shop.
R. R. Age Gazette.
Modern Artificial Lighting.
Knit Goods, Jan. and April, 191 1.
Morrison, D. P.
Railway Classification Yard Lighting.
Proceedings of Eng. Society of Western Pa., Oct., 1914.
Wade, F. K.
Lighting Problems.
Silk, March, 191 1.
Walker, G. W.
Artificial Illumination of a Modern Machine Tool Plant.
111. Eng., vol. 6, No. 11.
904 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
DISCUSSION.
Mr. R. B. Ely: Several questions have occurred to me in
reference to the use of mercury-vapor lamp, particularly where
it is used around iron and steel works. There are a great many
markings on the iron which indicate the relative positions for
placing the various pieces together, etc., and I was wondering
whether the red chalk or red paint marks would show dis-
tinctly under the light from this lamp. I know there has been
some trouble experienced in determining red markings, the red
pencil marks on packing cases calling attention to special ship-
ments, for instance. The red might appear black under a mer-
cury-vapor light. Now on an iron surface would the red chalk
marks show up at all, or would they appear of a different color?
Mr. W. A. D. Evans (In reply) : The red chalk marks would
not appear a bright red under the mercury-vapor lamp, but will
appear a dark brown. With a little practise, however, one could
very easily differentiate. We use the mercury-vapor lamps in
our office and, of course, in our ledgers both red and black ink
are used to indicate different accounts, and the clerks do not
have any difficulty in distinguishing one from the other, and I
know the same condition occurs in other cases.
benford: the parabolic mirror 905
THE PARABOLIC MIRROR.*
BY FRANK A. BENFORD, JR.
Synopsis: The following discussion of the parabolic mirror is divided
into two main sections, one devoted to such mirrors with a spherical light
source and the other devoted to mirrors reflecting light from a disk source.
These two types of sources are ideal cases of incandescent and arc lamps,
respectively. Preceding the two main sections a short discussion of a
parabolic mirror with a point source is given. In ordinary photometry
the fiction of a "point source" is highly useful and may usually be used
without question as to its accuracy. However, all present known light
sources fall far short of performing as a "point source" when placed at
the focal point of a parabolic reflector.
A searchlight, or headlight, consists of a source of light, usually
of small area and high brilliancy, placed at the focal point of a
parabolic mirror, or some nearly equivalent form of reflector.
There is an extremely large number of uses that may be found
for an intense beam of light of small angular width. In military
and naval service, in all types of navigation, and in nearly every
type of land transportation, the searchlight and headlight play a
highly important part. There is also a large field for the search-
light in flood lighting and spectacular work. In all of these
various types of service the principles of design are the same,
and the difference between one searchlight and another is a differ-
ence in degree, not in principle.
SYMBOLS.
F — focal length of mirror, in inches.
D — diameter of mirror, in inches.
R — radius of mirror, in inches,
r — radius of light source, in inches,
m — coefficient of reflection of mirror,
s — area of light source, in square inches.
Ia — intensity of light source at angle a from axis of mirror, in international
candles.
Ib — intensity of beam, in international candles.
B — brilliancy of light source, in candles per square inch.
L — distance from focal point to point in beam, in feet.
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
906 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
A — area illuminated, in square feet.
E— illumination on a plane normal to beam, in foot-candles.
Q — light flux, in lumens.
a — angles measured about the focal point of mirror, in degrees,
b — beam angles measured from the axis of mirror, in degrees,
e — angle subtended by the radius of the source at any point on the mirror
in degrees.
PARABOLIC MIRROR AND POINT SOURCE.
In all that is to follow, the mirror is assumed to be ideal in
form. The variations that occur in practice represent manufac-
turing problems and difficulties and need not be considered here.
\ 1
a
i
t
C
I
\
/
\
Figs, i and 2. — Parabolic mirror ; equation of generating curve.
The parabolic curve from which the parabolic mirror is gene-
rated by rotating the curve about its axis has for its equation
either
y = 4** (o
the rectangular form, see Fig. i, or
2F
(2)
1 + cos a
the polar form, see Fig. 2.
Using the rectangular form of equation, we have
y = 4F*
and the slope of the line drawn tangent to the parabola at point
P, Fig, 3, is
dy _ 2F
dx y
= tan c,
(3)
benpord: the parabolic mirror
907
(6)
(7)
The slope of the normal to the curve at this point is
J?L = - -*- = tan e (4)
~~ dy 2F
From the figure, light emitted from the focus follows the line
OP, and
y co
tan a = ^^j^
a _j_ c + d = 180
tan (a + c)= tan (180 - d) = tan d
and from (3), (5) and (7), we obtain
tan^-f (»)
From the law of reflection of light, we have
d' = d,
and, therefore, as tan c and tan d are numerically equal,
d' =c
and the reflected ray PC is parallel to the axis.
(9)
Figs. 3 and 4.— Parabolic mirror and point source.
A beam of light made up of rays such as PC would form a
true cylinder of unvarying diameter. Each ray would pursue an
independent path parallel to all the other rays, and hence, the
intensities of flux found in any cross section of the beam would
be identical with the intensities in all other cross sections. It is
908 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
obvious that in this case we may find the flux density or illumina-
tion at any point of the beam, but we may not assign any candle
intensity to it. The beam has some of the properties of a beam
coming from an intense source at an infinite distance. These
conditions are as physically impossible as the "point source" that
was assumed in the beginning.
It may be shown that the flux intensity in any section of the
beam db, Fig. 4, is equal to the flux intensity at a distance p from
the source before reflection takes place.
Let a small area dA on the surface of the mirror be illuminated
from a point source at the focal point. The cone of light striking
this area has an angle of incidence ix, as shown in Fig. 4. The
spherical area of this cone at the radius p is
ds — dA cos ix square inches (10)
The right section of the reflected beam has an area
db = dA cos i2 square inches (11)
and as r, = z2 degrees (12)
db = ds square inches (13)
The areas db and ds contain the same quantity of light, AQ,
and, therefore, the density is the same.
The intensity of radiation at radius p is
E = — foot-candles (14)
p' =y + (F — x)\ from Fig. 1.
= 4F* + F2 — 2F* + x2
= F2 + 2F* + x* = (F + x)2 inches2 (15)
E = (F + xy foot-candles (16)
and with a mirror having a coefficient of reflection m the beam
intensity is
E = (p^ xy foot-candles ( i7)
In Fig. 5 the beam intensities are plotted for a source having
a uniform intensity of one candle in three typical 18-inch (45.7
cm.) mirrors. The angular openings of the mirrors are, measur-
ing from the axis, 6o°, 900 and 1200.
benford: the parabolic mirror
909
PARABOLIC MIRROR AND SPHERICAL SOURCE.
In solving for the beam characteristics of a spherical source in
a parabolic mirror, it is necessary to make the assumption that
the distance across the mirror is very small in comparison to the
distance out along the axis of the beam where the intensities are
to be calculated. The effect of distance on the apparent intensity
of the beam will be taken up later.
K\
!\\ !
1 \!\l
\ vs
1
\
V*
y
9
■^^
i
1
1
1 4
1
,
0
l/f]
VI
r~~ CJ^SV^X-^S .
Fig. 5.— Parabolic mirror and point source beam characteristics.
Fig. 6.— Parabolic mirror and spherical source.
In Fig. 6, two small sections of the mirror, Px and P2, reflect
two rays which at a considerable distance from the mirror will
overlap. If the distance is great enough the areas A1 and A2
become very large and the distance 2y between their centers may
be neglected.
9IO TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Assume the plane area of a great section of the spherical source
to be j square inches, then the areas Ax and A2 are found by the
proportion
or A =sf — J square feet (18)
The shaded section of mirror, Fig. 6, may be considered as a
ring of small elements Plf P2, etc., all at the same distance P from
the focus.
The quantity of light reflected from the ring is
AQ = 2TrmI sin a Aa lumens (19)
I is the intensity of the source, assumed to be equal in all direc-
tions, and m is the coefficient of reflection of the mirror.
The illumination from the ring is
A
2irml sin a Aa .
foot-candles (20)
<¥)'
From equation (2)
2F
P =
1 -f cos a
and
877-wIF2 sin a Aa
AE =
sV(i + cos a)'
- __ 87rwIF'l sin a da
sV \ (l+COStf)2
_4ttwIF2 2 .
— ~7l7 — tan H«n foot-candles (21)
This is one form of the equation for the central density of a
beam from a spherical source and a parabolic mirror. With a
fixed focal length, the intensity varies as the square of the tangent
of half the angle alt or given a fixed angular opening, the inten-
sity varies as the square of the focal length.
benford: the parabolic mirror
911
We may write
— = B
s
(22)
the brilliancy in candles per square inch, then (21) becomes
4irwBF2
V
tan2 y2a1 foot-candles. ... (23)
This equation is particularly valuable as it shows that the inten-
sity at the center of the beam depends upon the brilliancy of the
light source and is independent of the size of the luminous sphere.
This has an important bearing on the design of incandescent fila-
ments for searchlights, etc.
The above equation may be written
twiBR2
E =
L2
foot-candles (24)
g
£
-p
t
?
\s>
C*7f*£*£- £-^
Fig. 7. — Parabolic mirror and spherical source beam characteristics.
The focal length does not enter into equation (24), and this
brings out the highly interesting fact that all parabolic mirrors
having the same diameter should give the same illumination at
points on the axis. The difference in action between a shallow
and deep reflector is shown in Fig. 7, where the beam intensities
of three 18 in. (45.7 cm.) mirrors of different focal lengths are
plotted. The same source, having a uniform brilliancy of 1,000
candles per square inch and a diameter of 0.5 in. (1.27 cm.), is
used in all three mirrors.
912 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
The two latter equations, by a simple transformation, may be
used to calculate the candle intensities on the axis.
Ib = 4twBF2 tan2 y^ ax candles (25)
and Ib = 7rR2Bw candles (26)
The last equation states that the intensity of a searchlight beam
is equal to the product of the brilliancy of the source, the plane
area of the mirror and the coefficient of reflection.
3^'
i :: :~:~t\ :::: :: :: :: :__
I U-^
t_ \>^
3 \ _^ __
N \
:" ::::::::: ::v: :: :: :vi:~
A. A A
Fig. 8. — Parabolic mirror and spherical source. Angular width of beam from
different radii on mirror.
The intensities at points not on the axis of the beam may be
found by the use of (26) and the following relations:
The apparent angular radius of the source viewed from the
central point on the mirror is
e0 = tan"
Po
tan"
_I -=%■ degrees
V
(27)
At other points on the mirror we have as a good approximation
Po ,
e = e0 — degrees
P
(28)
The light incident upon the center of the mirror has the greatest
spread and is distributed throughout the entire beam. The light
from the edges of the mirror is concentrated within a smaller
angle and this light forms the center of the beam. By noticing
the angle of spread at different parts of the mirror, the area
covered by any section may be readily obtained.
Values of (28) for the three mirrors of Fig. 7 are given in
Fig. 8. The angle of spread of the beam, b, is equal to the angle
subtended by the source, e.
benford: the parabolic mirror 913
The curves in Fig. 8 may be interpretated as follows : Suppose
an observer to stand at a considerable distance from mirror C
and slowly approach the axis of the beam. When he reaches a
point 5. 50 from the axis the center of the mirror will become
visible. At a point 50 from the axis the luminous spot will be
1.7 in. in radius. The luminous area will continue to grow until
the observer reaches a point 1.380 from the axis when the entire
mirror will be covered. From this point to a similar point 1.380
on the opposite side of the axis, the area and the total apparent
beam intensity will remain constant, and from this point the
luminous area will appear to decrease until the observer steps
out of the beam at 5. 50.
It is rather difficult to actually observe the action of the lumi-
nous spot on the mirror as outlined above on account of the
great distance at which the observer must stand. At an insuffi-
cient distance the mirror will first appear luminous at the center
and the edge nearest the observer. These two spots will merge
and form an oval area that gradually approaches the size of the
mirror as the observer comes up to the axis of the beam.
Under ideal conditions the area of the mirror that is active is
found from (28), and this area substituted in (26) gives the
beam intensity at the beam angle b.
The illumination curves in Fig. 5 seem to differ in practically
every respect from the beam intensity curves in Fig. 7. If foot-
candle readings are taken very close to the surface of the mirror
of Fig. 7 the illumination curves will be found to approach the
point source curves in form. The two sets of curves represent
the conditions at opposite ends of the beam. Between these two
extremes of distance, zero and infinity, the beam undergoes a
gradual transformation, and it is in this region of transformation
that our practical interest is centered.
When tests are made to determine the beam characteristics of
a searchlight one of the first questions that comes up is the
question of the proper testing radius. It is well known that the
apparent intensity and angular spread of the beam may vary at
different distances, and that tests made at relatively short dis-
tances are unreliable.
One of the most desirable conditions of a searchlight test is
914 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
that the data may be used to calculate illumination at various
distances by making use of the inverse square law.
The intensity of the beam has been shown to be proportional
to the area of the mirror, that is, with a given source, all para-
bolic mirrors have the same brilliancy. Equation (26) may be
rewritten
— — = mB candles per square inch
7rK.
(29)
The beam candles divided by the area of the mirror gives
mirror brilliancy
Bm = mB candles per square inch (30)
and it is at once evident that the beam has a maximum and con-
stant candle intensity at all points receiving light from the entire
mirror.
co /g /w-s>/rcw
Fig. 9. — Parabolic mirror and spherical source. I,aw of inverse squares.
Once the intensity reaches a constant value the inverse square
law may be used to calculate illumination at other distances, within
what is called the inverse square region in Fig. 9. The boun-
daries of this region are formed by the rays from the extreme
edge of the mirror.
The angle which the boundaries make with the axis may be
found from equation (28) or calculated directly.
tan"
1 — degrees
Pi
(30
where px is the distance from the focus to the edge of the mirror,
and the distance at which these boundaries cross the axis is
ho — — cot b. feet (32)
12
benford: the parabolic mirror
915
The following form, which is often more convenient, may be
used :
ho
»{''+*)
I2r
feet
(33)
The way in which the centers of the beams from the three
18 in. mirrors approach the maximum intensity is shown in
Fig. 10. These curves were determined by giving R various
values, and solving (33) for the distance L0 at which the maxi-
mum beam candles would be obtained, and with the same value
of R solving (26) for the intensity. If, in place of 18 in. mirrors,
we had larger mirrors of the same focal lengths, the points at
*.
«>■
j
'
rr ff'
3m
eao 00c
■s
^
f
>,
b
\
{
\ s&o 000
y
&
I uuu
'J
/
J
y
/
/
<
y
2
s
t
' V
*
,r
*
JJ
A
/
yn
A
0
eo £5
Fig. 10. — Parabolic mirror and spherical source. Apparent candles at points
on axis of beam.
which the beams come to full intensity could be found by extend-
ing the curves of Fig. 10. An increase in diameter will not affect
the axis intensity at points less than L0 because the added zone
of mirror will reflect a beam from points farther removed from
the axis and having a smaller angle of divergence, and hence, this
added part of the beam will reach the axis at points beyond L0
for the 18 in. mirrors.
It can be shown that there is considerable freedom of move-
ment allowed the light source without changing the central beam
intensity. This intensity has been shown to depend directly upon
the brilliancy of the source, and from this we could infer without
further proof that the size and shape of the source affects only
gib TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
the width and side intensities of the beam. The light on the axis
comes from those rays of the source that pass through the focal
point. It follows that the source may have any size, shape or
position whatever, without changing the central beam intensity,
providing only that every line from the mirror through the focus
will touch the light source.
" Fig. ii. — Parabolic mirror and spherical source. Freedom of movement of source.
In Fig. ii the sphere, which is the source of light, is shown in
two positions, Ox and 02. An inspection of this figure will show
that a line from any part of mirror A through F will touch the
source in either position, and in all intermediate positions. The
allowable movement either way from the focus is then
n = r sec a1 inches (34)
As the source is moved from Ox to 02 the width and shape of
the intensity curve will change, but the intensity on the axis will
not change. The point at which the inverse square region begins
will also shift as the source moves, being closest when the source
is at the greatest distance from the mirror.
With the source in positions Ox or 02, there will be a zone of
mirror B between Y*1 and P2 that will not be active in reflecting
light to the axis. With this mirror, and the deeper mirror C, the
source can be moved only through its own radius,
or n = r inches (35)
PARABOLIC MIRROR AND DISK SOURCE.
A disk, placed so that its luminous side is at the focal point
and facing the mirror, is the ideal case of the carbon arc. The
intensity on the axis of the beam is
IB = 7rR2Bw candles (36)
bexford: the parabolic mirror
917
The proof of this is almost identical with that given for a
spherical source and will not be repeated. For points not on the
axis the line of reasoning is not so simple, however, because the
beam from any small section of the mirror is elliptical in section
and the summation of these elliptical elements leads to compli-
cated mathematical forms. This is not a serious matter, however,
as the chief interest of an arc searchlight attaches principally to
the central beam intensity.
K
•
:
f.
1
bv
K
4^
1 :
is
" '
<
'
1
-r
LLP*
\j
\
s^
«
-z
Fig. 12.— Parabolic mirror and desk source. Beam characteristics. (Slopes
approximated) .
The width of the crest of the intensity curve is determined by
the angle subtended by the source from a point on the edge of
the mirror. From the point P1? Fig. 12, the disk appears to be
an ellipse having a major axis r, and a minor axis r cos ax. The
cross section of the beam from this element is an ellipse having
the same proportions.
The angular half- width of the flat crest of the curve is
b, == tan- x - — -1 degrees (37)
or
t>, = tan-
Pi
r cos a1
degrees
(38)
It has been assumed that the disk is luminous on one side only.
The part of mirror C between 900 and 1200 is not active. The
radius R in equations (36) and (38) must in this case be
2F
R = s = 2F inches (39)
1 — cos 90
918 TRANSACTIONS OF IEEUMINATING ENGINEERING SOCIETY
The width of the crest for mirrors B and C is zero. This is
evident both from the above expressions for e and from the fact
that the source appears to be a line when viewed from an angle
of 900. The overlapping line beams will give full intensity only
at the common crossing point.
The maximum width of the beam is
or
b0 = tan-1 — degrees
Po
b0 = tan-1 -=: degrees
(40)
(41)
The brightness of the mirror is as before
Bm = wB candles per square inch (42)
Fig. 13.— Parabolic mirror and desk source. Freedom of movement of source.
The boundaries of the inverse square region make an angle
b, = tan-1 degrees (43)
Pi
or
r cos a. , ,
bx = tan-1 =i degrees (44)
with the axis.
The distance at which these boundaries meet is
ho = — cot b1 feet (45)
or
R(F + a)
L„ = ^— feet (46)
12 r cos a.
benford: the parabolic mirror 919
Mirrors having an angle of 900 or over do not have an inverse
square region for the rays from the edge of the mirror are parallel
and do not meet.
The degree of freedom allowed a disk source is
n = r cos a1 inches (47)
either way from the focus. See Fig. 13. The movement for a
900 mirror is zero.
The beam characteristic at the surface of the mirror does not
follow the point source characteristic developed in the first sec-
tion. The intensity of radiation at angle a is
la = Io cos a candles (48)
and the foot-candle curve close to the mirror may be found from
the equation
E = (V+*)* foot-candles (49)
DISCUSSION.
Mr. J. L. Minick : Searchlights, and in fact all forms of light
units giving approximately parallel rays of light, are receiving
considerable attention at the present time and this paper will
undoubtedly be of great value in solving many of the problems
incidental to this class of lighting.
During the past few years about two thirds of the states and
territories have passed laws requiring the use of locomotive head-
lights of much higher beam candlepowers than are in common
use to-day. The requirements of these laws are usually very
indefinite due in some degree at least to the fact that they have
been prepared by persons having little or no technical knowledge
along lighting lines. In some instances the candlepower or wat-
tage of the lamp without reflector is the principal requirement;
in others the diameter of the reflector only is given ; in still others
the distance at which an object can be seen is specified, while
the speed of the train, weather conditions, color of background,
etc., are not even referred to.
The railroads have been faithfully trying to solve this prob-
lem and papers of this kind will be of material assistance in this
connection. The principal objections to the lawrs now existing
are, as stated above, their requirements are very vague and in-
6
920 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
definite and the requirements of adjoining states usually differ
from each other, so that one kind of headlight is required in
one state and another kind in another state.
I am not prepared to discuss the technical features of Mr.
Benford's paper to any great extent as my work has generally
been along slightly different lines. I have done some work,
however, that checks closely with Mr. Benford's work.
Mr. Benford states that in the application of the law of inverse
squares, the distance is measured from the reflector. I presume
the focal center is the point from which it is intended that this
measurement is to be made. I have discussed this question with
several authorities on parabolic reflectors and semaphore lenses
and I am told that in the case of the parabolic reflector the
measurement should be made from the center of gravity of the
longitudinal section of the reflector which will be found on the
axis of the reflector at a distance from the front of the reflector
equal to one third the total depth of the reflector. In the case
of semaphore and inverted semaphore type lenses the distance
should be measured from the flat surface of the lens.
I should like to see some investigation of lenses of the above
described types for headlight service. They can be readily
cleaned, they require no polishing and on the whole are much
more desirable for this class of service than are metal reflectors.
The polishing of metal reflectors very quickly destroys their re-
flecting surfaces, making it necessary to continually replate
them.
Dr. C. E. K. Mees: The beam brightness with the parabolic
mirror is the brightness of the source multiplied by the reflecting
power or transmission coefficient of the lens or mirror involved.
That being so, since the road brightness is as the candlepower of
the source, it is obvious that what is required is to produce as
large a source as possible. The remedy in fact, for glare in head-
lights is fairly simple, in that if one produces a large source — it
must be remembered that in an automobile headlight a very long
beam is not required — on ccan produce a large road brightness
with a comparatively small glare. Unfortunately the tendency in
automobile headlights is toward the development of extremely
bright, concentrated sources as shown by the production of
THE PARABOLIC MIRROR 921
6-volt lamps of as much as 72 candlepower, all concentrated into
an extremely small spherical filament. When you start to apply
the remedy to your own headlight, the practical difficulty is, how
to do it ? No ground glass at present made and no opal glass has
a sufficiently high diffusing coefficient to diffuse the modern
tungsten lamp. What is needed is a globe for a lamp, since the
automobile headlight has no medium to carry a diffusing screen,
a globe which shall be sufficiently diffusing to produce an evenly
diffusing surface for the high power lamps used. One can get a
wide beam with as little as a hundredth or perhaps a thousandth
of the glare now existing, and still get the total illumination, be-
cause a driver wants to clearly see the sides of the road; so it
seems to me that we must look to the lamp makers to produce
such a diffusing globe for their high candlepower automobile
lamps, and then we can bring pressure to bear on municipal
authorities to compel the adoption of diffusing globes on auto-
mobile headlights.
Mr. J. R. Cravath : There seems to be considerable miscon-
ception about the real problem to be met in the case of automo-
bile headlights, in reducing the blinding effect. Replacing the
clear glass of the headlight by a diffusing glass, reduces the
maximum effective candlepower of the beam many hundreds of
times ; in other words, it spreads out the beam very nice for illum-
inating the weeds alongside the roadway, but most drivers object
to it for country road driving as not throwing enough light far
ahead. I presume we have all thought of directing the light so
that it will be confined to the surface of the roadway and not into
the eyes of approaching drivers. But the practical difficulty is
that road inequalities will raise the beam in many cases, and
furthermore, it is very difficult to design reflectors and place
lamps accurately enough in practise so that there will not be suf-
ficient spread in the beam to catch the opposing vehicle driver in
the eye. The practical way out of it seems to be to require all the
powerful headlights to be turned off when on lighted city streets
and go only with marking lights, which is entirely practicable, and
is required in some cities. Most of the city ordinances on this
point are very indefinite. The city of Chicago prohibits a blind-
ing, dazzling or confusing light but does not define what such a
922 TRANSACTIONS Of ILLUMINATING ENGINEERING SOCIETY
light is. I found upon inquiry at the municipal bureau that is
established for that purpose, that it is a light that a certain com-
mittee of three looks at and decides to be such. (Laughter.)
Dr. E. P. Hyde: I recall some years ago that a committee
of the National Electric Light Association presented a report
on street lighting, and I think the aspect of the report that
impressed most of us most strongly was the apparent indecision
regarding the desiderata of street lighting. It is rather dif-
ficult to formulate specifications for street lighting when there
is no agreement on the requirements that are to be met by the
specified installation, and it has seemed to me for sometime that
the same condition exists regarding automobile lighting and the
question of glare, — the desiderata which are to be met in de-
signing a proper automobile lighting scheme are not definitely
agreed upon. We are impressed more with the case when we
hear, as we have heard this morning, more or less divergent
views regarding the matter. I think that on the one hand lamp
makers and the makers of the automobile headlights them-
selves have been endeavoring to get as nearly as possible the
full value of a parabolic reflector by having a point source and
keeping the light cone narrow. On the other hand, Dr. Mees
suggests that the great difficulty with it is the fact that there
is a narrow light cone. Now those two views are diametrically
opposite and the question arises as to just what we do want
in the way of illumination by automobile headlights. I think
that this Society should take some action in the matter. The
question of automobile headlights is one of the livest questions
of the day, and I do not know any body in the country to whom
the problem should be presented for consideration and action,
other than the Illuminating Engineering Society. I should like
to recommend — I don't want to put it in the form of a motion —
but I should like to recommend that this Society take some
action whereby a consideration of this question is definitely
undertaken either by some of the existing committees or by
some committee formed for the purpose in order that the Soci-
ety may, if possible, arrive at some conclusions which can be
suggested to those who desire to know them and may, in a way,
serve as a basis for specifications for automobile headlights, with
THE PARABOLIC MIRROR 923
the hope that in time the municipalities and counties may adopt
these specifications in order that there may be a uniformity
throughout the country and in any one city the specifications
may be such that an automobile driver may be able to know with
certain positiveness that his headlight conforms to the require-
ments and not be subject to the vagaries of committees of three
or any one of the committee of three who may happen to be
the victim in the case. With regard to the problem itself, I
think that we still are far from knowing the most important
elements that enter into producing what we term a glare. I
know that it is frequently considered that brightness of the
source itself is the principal element, and possibly it is. I
would gather from Mr. Cravath's remarks that he thinks that
the size of the searchlight in some way affects the brightness.
As I see it, if the mirror is a true parabola and if the light
source a point source or approximately a point source, the
brightness is not affected by the size of the parabolic mirror; it
is the same whether you have a large or a small parabolic mirror,
so long as you have a parabolic mirror. I think there is another
element, however, besides brightness which determines glare, and
I believe that each of you could convince himself of it if you per-
form a rather simple experiment. I think you will find that the
glaring effect, considering the contrast between the source at
which you are looking and the surroundings to be the same in
each case — because of course contrast is a very important ele-
ment— is determined not only by the brightness of the source
but by the total flux of light. I remember some years ago we
performed in our laboratory a very simple experiment; we set
up a Nernst glower and a condensing lens in such a way that the
image of the glower was formed on the cornea. The lens was
seen to be filled with light. You did not change the brightness of
the source by changing the aperture of the lens, but you could
change tremendously the glaring effect by changing the effective
size of the lens which changed the amount of light coming into
the eye. I think you will find that the two elements enter ; there
may be other elements which enter, but it seems to me we should
undertake to determine in this Society, in some rather definite
way, ( 1 ) what the elements are that produce the glare and how
to avoid them, and (2) what the desiderata in automobile head-
924 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
lights are, and endeavor to draw up some specifications by which
these desiderata may be met.
Mr. L. C. Porter: Taking up the question of the spread of
the beam, it is obvious that for headlight work, for example, a
very narrow pencil of light is not satisfactory. That brings in the
question of how you are going to determine the spread of the
beam; in other words, where is the edge of the beam? What
figure can you take? If you had a theoretical point source, you
could have a sharp edge beam, but with the sources which are
practical — the arc crater and especially the incandescent lamp
filament — the beam does not have a sharp edge.
In specifying a headlight there must be some method used to
take into account not only the maximum candlepower of the
headlight, but also the spread, and I should like to ask Mr. Ben-
ford if he has any suggestions as to how he would determine the
edge of the beam. For practical manufacturing we must have a
method of rating headlights which takes into consideration the
spread, the average intensity across this spread, as well as the
pick-up distance. I should like to see the valuable theory in this
paper supplemented by some of the practical problems which
must enter in the manufacture, testing and use of searchlights.
The incandescent lamp is having a very widely increased ap-
plication to headlight service. It is possible now, with six-volt
lamps of about 150 candlepower (a standard lamp) to get over
900,000 beam candlepower from a 20-inch parabolic mirror, and
many such headlights are now in service. With a little more
powerful lamp one is able to obtain considerably over a million
in beam candlepower. Such beams are applicable to navigation
service, and many other classes of work which do not require
extremely high candlepower beams.
On the eleventh page, Mr. Benford gives a formula which
shows the distance at which one can begin to measure beam
candlepower. In practise you can generally obtain more accurate
results by using considerably greater distances than the minimum
which the formula shows. At this distance, the intensity is so
high that it is difficult to measure it with a photometer, but if
you go off several hundred feet you can get photometric readings
fairly accurate.
THE PARABOLIC MIRROR 925
In regard to the question of automobile headlights, in New
Jersey there is a rule forbidding the use of headlights which
produce glare, and a commissioner passes upon devices which
eliminate glare. It may be of interest to you to know of some
of these devices which have been approved. One of the first
schemes was to dip the upper two thirds of the front glass of the
headlight in either an opal or an amber dip, amber being recom-
mended. As has been pointed out, that has the disadvantage of
largely reducing the illumination on the road. Another method
is to put a dip on the lamp itself, this dip generally being opal
and taking a form which will cover the lower half of the bulb
and the direct rays from the filament itself. Another method
which has been approved is to paint or paste paper on the lower
half of the parabolic reflector, i. e., dull it by some method. Still
another one is the use of a Venetian blind effect across the front
of the headlight, the idea of this being that it will protect the
pedestrian's eyes but will let the light go down on the road.
Another method in common use is a small candlepower lamp in
the top of the reflector. Still another one is the use of resis-
tance to simply cut down the candlepower of the light for city
driving. In New Jersey such a device is not acceptable ; the rule
states that no device will be acceptable which is within the control
of the driver. That seems to be a little unreasonable. For city
use, a powerful beam is not required because the cars move
slowly and the driver has the street lamps to help out, and either
the method of reducing the candlepower of the lamp by resis-
tance or turning on a small lamp and extinguishing the main
lamp gives perfectly satisfactory illumination. In the country
one should naturally be able to use a more powerful beam, be-
cause there, one drives faster. As Mr. Cravath has pointed out,
it is not a very simple matter to direct the beam down on the
road because the distance at which a driver wants to see the road
varies with the speed of the car, and at the same time the driver
must be able to see down on the immediate foreground. It is
very difficult to drive with a bright spot of light several hundred
feet ahead and darkness in the immediate foreground of your car.
Another method which has been used to some extent is the use
of lenses to more or less accomplish this, and I believe that Dr.
Gage is going to say something on that subject.
926 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
I thoroughly agree with Dr. Hyde that there should be further
research on this question and that the Illuminating Engineering
Society should cooperate with those having to do with the
automobile industry in this work. I do not feel that the glare
reducing device should be a part of the incandescent lamp itself.
The lamp should be as simple as possible and applicable to any
kind or type of headlight. The sockets in many headlight equip-
ments are not adjustable ; therefore, a glare reducing device if
put on the lamp itself might be satisfactory for one car and not
for another.
One method which can be easily applied to the lamp, though,
and which has been applied to some of the high candlepower
tungsten lamps is to all-frost the bulb having a concentrated fila-
ment. With the all-frosted bulb there is enough of the main
beam left to show light at a distance, and yet the all-frosted bulb
gives considerable light in the foreground and reduces the glare
somewhat.
I have felt that good results might be accomplished by the use
of polarized light either having two sets of tourmaline crystals
for the front glass of the headlight, or one set on the headlight
and the other set used by the driver for goggles.
Dr. H. P. Gage : I should like to add something to Mr. Ben-
ford's paper on the theoretical calculation of the intensity of
the beam as obtained by the use of semaphore lenses. The re-
sults come out very similar to those of the parabolic reflector.
We start out with a certain intrinsic brilliancy of the source,
which we can call I or S. The lens or mirror re-directs the light
from this source into a practically parallel beam. All actual
sources which it is necessary to consider are not point sources,
but extended sources ; consequently, looking at this lens from in
front, at any reasonable distance for which the lens is to be used,
the apparent size of the source is magnified so that it covers the
entire front surface of the lens. The simple method of calcu-
lating the candlepower in this case is to multiply the intrinsic
brilliancy of the source by the area of the lens, and by some
factor which in my experiments I call area efficiency, and which
Mr. Benford calls reflective efficiency. As the lens is seen from
the front, one gets an appearance of a solid disk of light inter-
THE PARABOLIC MIRROR 927
rupted by dark rings. The average intrinsic brilliancy of the
lens is reduced by those dark rings as well as by the reflection
losses and absorption losses of the lens itself.
Regarding the comment as to where, when a lens is set up, the
distance from the lens should be measured — the distance is
measured from the edge of the lens, because the lens appear as
a luminous disk of light. At the Corning Glass Works we
specify the projected beam as follows: First, the apparent
candlepower of the center of the beam, calling that the beam
intensity. For the spread of the beam, we take the angle between
the two directions where the intensity has fallen off to 50 per cent,
of the axial intensity and call it the spread of 50 per cent, in-
tensity. For signal purposes, the angle between the directions
where the beam shows about 1 candlepower is called the ex-
treme spread. The spread of 50 per cent, intensity would, I
think, be a good measure to take for the spread of beam with the
different headlight reflectors.
I should like to make a few comments on the parabolic re-
flector as used as an automobile headlight and some of the de-
vices for reducing glare. Frosting the upper two thirds of the
reflector has been suggested. Placing a small source at the exact
focus of the parabola, results in a perfectly parallel beam of light.
Any light source available is an extended source and generally
approximately spherical. The angle subtended at the center of
the reflector extended forward gives the spread from the apex
of the parabola, making the small spot in the center referred to
by Mr. Benford. At the extreme edge of the parabola, the
angle subtended by the source is very small; consequently there
is a very small spread ; that is, each zone of the reflector has a
different spread from every other zone, the outside being the
smallest. If the person setting up an automobile headlight
focuses the source inside the focus, the beam from the lower
clear part of the parabola is directed downward toward the road
exactly the same as though the whole headlight were directed
down. If, on the other hand, the lamp is set in front of the
focus the beam from the lower part of the parabola is directed
upward right into the eyes of an approaching automobile driver
and no illumination of the road in front of the lamp results. If
928 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
the Illuminating Engineering Society decides on specifications,
this device should be considered practically worthless. I have
had some slight experience driving an automobile against glaring
headlights, and perhaps what I can say will appeal to a number
of others as the result of actual experience. In meeting an ap-
proaching automobile, the glare seems to me proportional to
the intensity of the light; that is, the candlepower of the ap-
proaching light, and, as Dr. Hyde mentioned, the glare depends
on the square root of the candlepower rather than on whether
the headlight is of large or small diameter ; i. e., it is the question
of candlepower rather than of intrinsic brilliancy. The im-
portant criterion of glare is not the discomfort to the eyes of the
driver, but it is the question whether the driver can see beyond
the light. Some devices will reduce the discomfort of the op-
posing light, but do not increase the visibility beyond that light.
That question is coming up, and my suggestion of the solution
would be something as follows : Set up a large white screen,
perhaps larger than this blackboard, with a hole in the center
through which can be seen the headlight to be tested ; around the
opening paste or write on test letters such as are used by occu-
lists, twice the size usually employed for the given distance.
If the headlight is to be observed at 50 ft. (15.24 m.), use the size
for 100 ft. The test is made by illuminating moderately the test
letters and observing the conditions under which these letters can
be read and how close to the axis of the headlight they can
be read.
Norman Macbeth : My experience has been that the glare
effect of headlights depends more largely upon the extent of the
retina covered by an after image and the period of recovery
which is, of course, largely dependent upon the extent and nature
of the retinal burn. The solution of this problem lies in the
control of the light as against the more generally practised
methods of absorbing the uncontrolled and misdirected light. I
have driven many hundred miles making observations with head-
lights, particularly those where the beams are confined within a
very narrow angle — where a very narrow beam was directed
forward and downward along the road. The parabolic reflector,
the kind we experimented with, was shallow and intercepted only
THE PARABOLIC MIRROR 929
a third of the light flux generated by the lamp, and there was
considerable direct light from the lamp around the front of the
machine. I have driven in machines equipped with headlights
having proper reflectors and there is absolutely no light within a
safe distance of the eyes of approaching drivers.
Three or four years ago, when the amber glasses came out, the
manufacturers said, "The solution of the headlight glare is to
wear a pair of amber glasses." My personal opinion after road
tests, was that the amber glasses resulted in about the same effect
as if you closed your eyes when you were approaching a headlight
and opened them immediately after it had passed, thus eliminating
a burning of the retina and enabling you immediately to see the
road again.
There has been a great deal of foolishness attached to this
headlight proposition. One manufacturer, for instance, uses a
hemispherical globe on the front of the lamp, etching all but a
small clear spot below the center and makes the claim that "this
headlight is without glare because of the illuminated background
surrounding the high intensity spot." The illuminated back-
ground being 10 in. (25.4 mm.) in diameter, subtends but a
slightly wider angle and in area is far from being a background.
The real trouble is that headlights are part of a car equipment.
Manufacturers of automobiles to-day are putting out their cars by
the thousands and tens of thousands and I know manufacturers
who have supplied devices for automobiles one year and lost that
business the following year because their devices cost 5 cents per
car more than some other available device, and on fifty thousand
cars the saving was reckoned. The reflector for automobile
headlights, as used to-day, cost 60 to 80 cents. There was none
of this difficulty in the old type of lamps using acetylene,
not because they were gas lamps but because they used mangin
mirrors.
I made a test a short time ago with properly designed, well
made metal reflectors. I had two of these reflectors freshly
plated, polished and put in good condition; then I took one of
them and with a piece of fine emery cloth, carefully scratched the
surface of the reflector. This was just the cleaning process ex-
aggerated and that reflector had a light distribution as wide as
930 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
one would secure with a China dinner plate. The other reflector
confined the beam within 30 in a similar manner to a good ground
and polished mirrored glass reflector. Many hours of observation
with headlights having reflectors good and bad have convinced
me that a well made properly ground to shape, mirrored glass
reflector with a beam within 20 or 30 will meet all the just re-
quirements— that light should not be directed higher than 4 or 5
feet above the ground in order to protect both the driver and those
approaching a car so equipped. From one pair of such reflectors
I obtained a beam of 68,000 candlepower with 24-candlepower
lamps. The reflectors were shallow and intercepted less than half
the light generated.
A very simple and effective method was adopted for city driv-
ing. The lamp sockets were attached to a sleeve with a hinge
controlled by magnets in such a manner that by pressing a con-
venient button the lamp was moved up about an inch and out
of focus with the result that a large pear-shaped image of the
lamp filament was projected onto the pavement just in front of
the machine and forward for about 40 feet. My conclusion has
been that the solution of the headlight glare proposition is sim-
ply a matter of the control of light, which is not difficult unless
one is required to do it for an amount not exceeding one dollar
per lamp.
Mr. W. R. Mott : The headlights on automobiles are, most
of them, stationary, and it is perfectly possible now, with the
development of headlight turning apparatus, to turn the head-
light with the wheels. I have ridden in automobiles thus equipped
and noticed a great improvement in the lighting.
Dr. P. G. Nutting: I do not wish to take the time of the
Society with any further discussion, but I wish to make the an-
nouncement that this whole subject is adequately treated, I think,
in the report on automobile headlights of the Committee on
Glare.* In this report we have discussed the subject from ele-
mentary optics to model ordinances. A great deal of discussion
would have been saved if this report had been presented here.
Nearly all the questions raised this morning are answered in that
report.
* This report is to appear in the next issue of the Transactions.
THE PARABOLIC MIRROR 931
Mr. F. A. Benford (In reply) : Mr. Minick brought up the
question of measuring the zero point along the beam. I have
taken the zero point at the source. Actually the zero point should
be in the edge of the plane of the opening of the mirror. This
applies both to a lens and to any type of reflector. The difference
between the edge of the plane of the opening and the source is
ordinarily very small and may be neglected.
Dr. Mees' suggestion as to frosting the bulb was answered by
Mr. Cravath's saying that the intensity of the beam would be
reduced in the same proportion as the intensity of the parent
source.
Dr. Mees : I suggested the frosting of the bulb and Mr. Cra-
vath was talking about the frosting of the lens.
Mr. Beneord: It works out somewhat the same, though.
Dr. Mees : Not at all.
Mr. Benford : In reducing the candlepower in the center,
I mean.
Dr. Mees : Not in distribution.
Mr. Benford : Mr. Porter brought up the question of the
edge of the beam with a view of establishing some percentage
of intensity which may be called the edge. That may be done
for certain classes of work and yet would not be a good thing as
a rule. Take the automobile headlight, as an example, the in-
tensity of one candlepower at an angle of 45 ° downward from
the lens will produce more illumination, on the average, than
10,000 candlepower in the center of the beam, because of the
great distance at which the center will strike the road and the
high angle of incidence ; so if one puts an arbitrary edge to the
beam at 10 per cent, of the center intensity, one will be losing
much of the effective light.
932 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
ULTRA-VIOLET RADIATION AND THE EYE *
BY W. E. BURGE.
Synopsis: Transparent, free-swimming, unicellular organisms, para-
mecia were exposed to the radiation from a quartz mercury burner and
observed under the microscope during the exposure. The organisms
became more and more opaque during the exposure and were dead after
30 minutes. The conclusion is drawn that ultra-violet radiation kills
living cells by coagulating the protein of the cells, as is the case when
they are heated to ioo° C.
A square of glass was covered with a thin film of egg white and per-
mitted to dry. A piece of cardboard with a circular area cut from the
center was fitted over the transparent film. This preparation was placed
10 cm. from a quartz mercury burner and allowed to remain for 30 hours.
Thus the circular area of egg white was exposed to the radiation while
that under the cardboard was not. At the end of the 30 hours the card-
board was removed. No difference could be seen between the exposed
and unexposed parts of the film of egg white. The preparation was
immersed in 0.1 per cent, calcium chloride for 10 minutes. The exposed
circular area became an opaque coagulum while the unexposed part
remained transparent. The conclusion is drawn that ultra-violet radia-
tion coagulates protein by changing it in such a way that certain salts
such as those of calcium can combine with it to form a coagulum.
The eyes of one batch of frogs living partially immersed in 0.1 per
cent, sodium silicate were exposed to the radiation from a quartz mer-
cury burner. The eyes of another batch living partially immersed in tap
water were also exposed. Those living in the silicate developed very
severe anterior eye trouble, while those living in tap water developed it
very slightly. The eyes of fish living in 0.1 per cent, sodium silicate were
exposed to the radiation from a quartz mercury burner for the same
length of time as those living in tap water. Those in the silicate solution
developed cataract, while those in tap water did not. The unmoistened
human skin was exposed to the sunlight as well as skin moistened with
water rich in calcium salts. The skin that was moistened sunburned
much more quickly and severely than that which was not moistened. The
conclusion is drawn that ultra-violet in the radiation from the quartz
mercury burner and from the sun produced these injuries by modifying
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
BURGE : ULTRA-VIOLET RADIATION AND THE EYE 933
the protein of the cells of the crystalline lens and of the skin in such a
manner that the salts present can combine with it to form a coagulum.
Cataract is prevalent among people living in India and among glass
blowers. Analyses of human cataractous lenses from the United States
show a great increase in the salts of calcium and magnesium and those
from India in addition an appreciable amount of sodium silicate. Tropical
light is comparatively rich in ultra-violet radiation. Silicious earths form
part of the diet of certain classes in India. To explain the prevalence of
cataract among people living in the tropics and among glass blowers the
assumption is made that ultra-violet radiation modifies the protein of the
lens so that the salts of calcium and of magnesium and sodium silicate
when present in abnormal amounts can combine with the modified pro-
tein of the lens to form a coagulum and hence an opacity or cataract.
The wave-lengths in the ultra-violet region of the spectrum effective
in changing the protein so that certain salts can combine with it to form
a coagulum lie between 254MM and 302M1" inclusive.
It has been recognized for some time that, unless protected
by a glass globe, the radiation from a quartz mercury arc or
from an iron arc or from any light source emitting large quan-
tities of ultra-violet rays is harmful to the eye. In a general way
it has been assumed that all radiation of shorter wave-lengths
than 350/n/n is injurious to living tissues. So far as I know little
or no attention has been paid to the mode of action of this radia-
tion in producing the injury. The object of this investigation,
among other things, was to determine which wave-lengths in the
ultra-violet region of the spectrum are injurious to living tissues
and the mode of action of these wave-lengths in producing the
injury.
An organ, e. g., the eye, is composed of tissues, connective
tissue, nervous tissue, etc. The tissues are composed of cells.
The most important constituent of the cell is the protein. Pro-
tein is a nitrogenous, semi-fluid organic compound, colloidal in
nature. Egg white is a good example of a protein. This, how-
ever, consists of several proteins. Dreyer and Hanssen1 showed
that egg white is converted into an opaque coagulum by exposure
to ultra-violet radiation just as it is when it is heated to ioo° C.
I exposed free-swimming organisms, paramecia, to the radia-
1 Dreyer and Hanssen ; Comptes Rendus, 1907, vol. CXI<V, p. 234.
934 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
tion from a quartz mercury burner and observed them under the
microscope during the exposure. These organisms are fairly
transparent and are just visible to the unaided eye. During the
exposure they moved more and more slowly and gradually
became more granular and opaque. After twenty or thirty min-
utes the organisms were dead. Fig. I ( I ) represents the normal
transparent animal, (2) represents an organism that was killed
by ultra-violet radiation and (3) one killed by heating to 45 ° C.
It may be seen that whereas the normal animal ( 1 ) is transparent,
(2) and (3) are both granular and opaque. As exposure of
egg white to ultra-violet radiation caused it to lose its trans-
parency and to become an opaque mass, so the exposure caused
the living material or protoplasm of these organisms to coagulate
and to become an opaque mass. The conclusion may be drawn
that ultra-violet radiation injures or kills living cells by coagu-
lating or rendering insoluble the protoplasm or living material
of the cells.
Experiments were carried out in an attempt to determine the
mode of action of ultra-violet radiation in coagulating or render-
ing insoluble the protein of cells and to determine the specific
wave-lengths in the quartz mercury arc active in this respect.
A normal excised crystalline lens was placed between two quartz
plates and pressed into a thin layer by squeezing the plates
together. By means of a quartz spectrograph the spectrum from
a quartz mercury burner operating at 70 volts and 800 candle-
power was focused on the layer of lens material. This layer of
material was almost perfectly transparent. The exposure was
made for one hundred hours. At the end of this time there was
no visible change in the material. It was as transparent as at
the beginning of the experiment. However, when the preparation
was immersed in a 0.1 per cent, calcium chloride solution four
bands of coagulated lens protein appeared where the bands of
the spectrum had been focused. Fig. 2 (3) is a photograph of
the preparation after it had been immersed in the calcium chloride
solution ; ( 1 ) is a photograph of the spectrum that was focused
on the material. It may be noticed that the lens material (3)
was precipitated in the extreme ultra-violet region of the spectrum
where the photographic plate (1) was not affected.
burge: ultra-violet radiation and the Eye 935
A similar preparation was made except that the lens was
soaked in a o.i per cent, solution of calcium chloride for several
hours previous to being pressed between the quartz plates. The
spectrum was focused on this layer of lens material just as it
had been focused on the layer of normal lens material. After
fifteen hours of exposure nine bands of coagulated lens material
could be seen where the corresponding bands of the spectrum had
been focused. Fig. 2 (2) is a photograph of the lens material
on which the spectrum had been focused for fifteen hours. The
line of coagulated lens protein in (2) where the spectral line of
wave-length 254/i/i was focused appeared after sixty minutes
exposure; that where the spectral line of wave-length 265^/1, was
focused after seventy-five minutes of exposure. The other lines
of coagulated lens protein where the lines of the spectrum was
focused appeared after two hundred minutes of exposure.
Egg white was introduced into a quartz cell. The spectrum
from the quartz mercury burner was focused on this material
for fifteen hours. At the end of this time nine bands of coagu-
lated egg white could be seen where the bands of the spectrum
had been focused. These bands of coagulated egg white occurred
where the bands of coagulated lens protein had occurred and
the time of appearance of the different bands was about the same
as those of the lens protein, (2) Fig. 2.
Egg white was poured on a glass plate and spread out in a thin
layer. After the egg white was dry the spectrum from the quartz
mercury burner was focused on it for fifteen hours. At the end
of this time no visible change had been produced on the egg
white by the spectrum. The glass plate with the layer of egg
white on it was immersed in a 0.1 per cent, calcium chloride solu-
tion. In a few minutes nine lines of coagulated egg white
appeared in the region of the spectrum where the lines of coagu-
lated lens protein had appeared.
From these experiments it would seem that calcium salts in
some way make it possible for ultra-violet radiation to precipitate
protein. It would seem that ultra-violet radiation acts on the
protein in such a way that calcium salt can combine with it and
form a precipitate or coagulum. Magnesium salts and silicates
have the same effect as the calcium salts.
7
936 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Cataract is an opacity of the crystalline lens. Analyses of
human cataractous lenses from America show a great increase
in the salts of calcium and magnesium and those from India show
in addition to these salts silicates. I am told that silicious earth
forms a part of the diet of certain classes in India. This may
account for the silicates in the cataractous lenses from there.
Cataract is of very common occurrence in India. Tropical light
is comparatively rich in ultra-violet radiation. To explain the
prevalence of cataract in India, the assumption is made that the
relatively great amount of ultra-violet radiation in tropical day-
light acts on the lens protein in such a way that the silicates in
the eye media can precipitate it and produce an opacity. To
explain the prevalence of cataract among glass blowers, the
assumption is made that the eyes of glass blowers are subjected
to more of the short wave-lengths than the eyes of people gen-
erally and for this reason the protein of the lens is modified and
if such substances as salts of calcium, magnesium or silicates are
present in sufficient concentration the protein will be precipitated
and the lens rendered opaque or cataractous. The glass blowers
who develop cataract form a relatively small percentage of those
engaged in that occupation. Since the eyes of those who do and
those who do not develop cataract are exposed to the same quality
and quantity of radiation from the furnaces, it is assumed that
those who do develop it have a disturbed condition of nutrition
expressing itself in an increase of those substances which can
precipitate the protein of the lens acted on by ultra-violet
radiation.
PRODUCTION OF AN OPACITY IN THE LENS OR
CATARACT IN LIVING ANIMALS.
Experiments were carried out in an attempt to increase in the
fluids of the body of living animals and hence in the eye media,
those substances found to be greatly increased in cataractous
lenses with the hope that on exposure of the eyes of the animals
to ultra-violet radiation cataract would develop. Many observers
have demonstrated that it is impossible to produce an opacity of
the lens or cataract in a normal living animal by exposure of its
eye to ultra-violet radiation. Burge2 showed that it was im-
2 Burge ; Amer.Jour. o/Phys., vol. XXXVI, 1914.
Fig. i.
-Paramecia. (i) the normal transparent animal. (2) Paramecium killed by ultra
violet radiation. (3) Paramecium killed by heating to 450 C.
1 Sl 3 1
400^
436,
4 04.
36&.
31.T
302
297
289
1 *0'
2 80
276
2 70
265
120'
.ao.o'
..2o.p- ...
.I.6.V....
2S4
_..5.0'. .
249
.2. P. P.'...
Fig. 2.— Photograph of spectrum of quartz mercury arc. (1) Made on a photographic
plate. (2) Made on lens protein extracted by 0.1 per cent, calcium chloride. (3) Made
on a thin layer of lens, immersed in 0.1 per cent, calcium chloride after the exposure.
Fig. 3— Fish (1) living in tap water and exposed to ultra-violet radiation for 12 hours.
Fish (2) living in 0.1 per cent, sodium silicate and exposed to ultra-violet radiation
for 12 hours. Fish (3) living in 0.1 sodium silicate and exposed to ultra-violet radia-
tion for 24 hours.
Fig. 4- — Frog (i) living in tap water and exposed to ultra-violet radiation for 5 hours.
Frog (2) living in 0.2 per cent, sodium silicate and exposed to ultra-violet radiation
for 5 hours.
burge: ultra-violet radiation and the eye 937
possible to produce an opacity of the excised lens exposed directly
to ultra-violet radiation for very long periods. Fish were chosen
for the experiments because they could be kept alive in the solu-
tions of the salts desired. One batch of gold fish was kept in
0.8 per cent, calcium chloride, another in 0.8 per cent, calcium
lactate, another in 1.0 per cent, dextrose, another in 0.1 per
cent, sodium silicate for ten days. At the end of this time each
fish in its turn was introduced into a small box with a quartz
window in one side. In practise four of these boxes were used
so that four fish were exposed at one time. Clear tap water was
kept flowing through these boxes during the exposure. The
boxes containing the fish were adjusted so that the quartz win-
dows were 15 cm. from a quartz mercury- vapor burner operating
at 140 volts, 3.3 amperes and 2,400 cp. In this manner one eye
of each fish was exposed to the radiation. Each exposure was
of six hours' duration. After the exposures the batches of fish
were replaced in the solutions from which they were taken. For
comparison the eyes of fish living in tap water were exposed in
the same manner and for a similar length of time as those living
in the salt solutions. As a rule a slight opacity in the cornea of
the eye exposed appeared about fifteen hours after the first ex-
posure.
Ten days after the first exposure the eyes of the fish that had
been exposed were exposed again for another six-hour period.
At the time of this second exposure as a rule an opacity of the
cornea and lens of the fish living in the salt solutions had increased
while the opacity of the cornea of the fish living in tap water had
cleared up. Several hours after the second exposure as a rule
the opacity of the lens and cornea of the fish living in the salt
solutions became more marked. An opacity of the cornea of the
fish living in tap water also developed, but it was slight and
cleared up in a few days, while that of the fish living in the salt
solutions increased.
After the second exposure no prescribed rule as to time for
the third exposure can be laid down. In order to clear up the
opacity of the cornea of the fish in the different salt solutions,
it is necessary to transfer them to tap water. As a rule the
opacity of the cornea will clear up in a few days, while the lens
938 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
remains opaque. By nursing, by exposing to ultra-violet radia-
tion, by transferring back and forth from salt solutions to tap
water, I have been able to obtain fish in the condition indicated
in Fig. 3. Fish 1 had been living in tap water in the laboratory
for thirty days and had been exposed to ultra-violet radiation for
two six-hour periods or twelve hours. Fish 2 had been living
in 0.1 per cent, sodium silicate for twenty-eight days and had been
exposed to ultra-violet radiation for two six-hour periods or
twelve hours. Fish 3 had been living in 0.1 per cent, sodium
silicate for forty-two days and had been exposed to ultra-violet
radiation for four six-hour periods or twenty-four hours.
It may be seen that the lens of fish 3 living in the silicate solu-
tion and exposed to ultra-violet radiation for twenty-four hours
had become perfectly opaque, that of fish 2 living in the same
solution but exposed to ultra-violet radiation for twelve hours
had become partially opaque, while the lens of fish 1 living in
tap water and exposed to ultra-violet radiation for twelve hours
was practically clear. The results of these experiments would
seem to support the assumptions made in explaining the preva-
lence of cataract among people living in the tropics and among
glass blowers.
THE PRODUCTION OF ANTERIOR EYE TROUBLE
BY MEANS OF ULTRA-VIOLET RADIATION.
One batch of frogs was kept partially immersed in 0.2 per cent,
sodium silicate, another in 0.8 per cent, calcium chloride, another
in 1 per cent, dextrose for fifteen days. The eyes of these frogs
were exposed to the radiation from a quartz mercury burner at
a distance of 20 cm. one hour each day for five successive days.
Photographs of the frogs were made fifteen days after the
exposures. Fig. 4, frog 2 had been living partially immersed
in 0.2 per cent, solution of sodium silicate previous to the
exposure. Frog 1 had been living partially immersed in tap
water for the same length of time. It may be seen that the skin
covering the anterior part of the eye of the frog living in the
salt solution had been coagulated and converted into an opaque
mass, while that of the frog living in tap water was very little
injured. The solution of calcium chloride and of dextrose had
the same effect as the solution of silicate. The conclusion may
BURGE: ULTRA-VIOLET RADIATION AND THE EYE 939
be drawn that salts such as are found to be greatly increased in
human cataractous lenses not only increase the effectiveness of
ultra-violet radiation in producing an opacity of the lens or cata-
ract, but they also increase the effectiveness of ultra-violet radia-
tion in producing anterior eye trouble.
The skin is more easily sunburned when it is wet than when
it is dry. Sunburn is a precipitation of the protein of the cells
of the skin by the ultra-violet radiation in sunlight. Ultra-violet
radiation acts on the protein of the cells of the skin in such a way
that certain salts in the lymph bathing the cells can combine with
it and precipitate it. If the skin is wet, the salts in the water
facilitate this process.
CONCLUSIONS.
i. Ultra-violet radiation kills living cells and tissues by chang-
ing the protoplasm of the cells in such a way that certain salts
can combine with the protoplasm to form an insoluble com-
pound or coagulum. The effective region of the spectrum in
coagulating the living material of the cell or protoplasm is
between 249/x/i and 302^. The most effective region is around
254/1/u, in case of the mercury arc used.
2. An opacity of the lens or cataract can be produced in fish
living in solutions of those salts found to be greatly increased
in human cataractous lenses by exposing the eye of the fish to
ultra-violet radiation. This cannot be done with fish living in
tap water.
Nela Research Laboratory,
National Lamp Works of General Electric Co.,
Nela Park, Cleveland, Ohio.
August 25, 1915.
DISCUSSION.
Mr. W. R. Mott: Referring to glass 1 millimeter thick not
absorbing ultra-violet light at 300/z/a, I think it makes an enor-
mous difference what kind of glass is used. The ordinary win-
dow glass really cuts off ultra-violet quite well ; therefore a state-
ment of the kind of glass1 referred to might be of advantage. I
1 Note on Non-transmission of ultra-violet (300/u.fi) through glass ; p. 94, E. C C Baly's
book on Spectroscopy ; p. 3, Plotnikow, Photochemische Versuchs-technik Lepzig, 1912,
Akademische Verslagsgesellschaft ; pp. 301 and 335, Eder's Handbuch ber Photographic,
1912; p. 608, Light Energy by Dr. M. Cleaves.
940 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
have made a few little experiments on the coagulation of albu-
men with different kinds of flame arcs. With the white flame
arc there is very little coagulation if cooled by air or water when
very near the arc. With an iron arc there is very marked coagu-
lation.
Relative to the point that some people who are afflicted with
cataract have diabetes, I call attention to the fact that uranium
has been used as a homeopathic remedy for diabetes, and in
large doses, undoubtedly produces conditions of chronic nephri-
ties. Uranium has another interesting characteristic : it responds
to the action of light in the presence of organic material, causing
very severe decomposition of almost any organic acid. The com-
bined action of the chemical and of light produces entirely dif-
ferent results from the action of either alone. The same is true
to a limited extent of iron, and this again raises the question :
What is the chemical reaction in some of these cases? In that
connection, I have been doing some experiments on dye fading,2
and in looking up the literature, I find that dyes ordinarily are not
faded if they are placed in a vacuum where the oxygen cannot get
at them ; and I saw a reference to the statement that bacteria are
not killed by ultra-violet light in a vacuum.3 I don't know how
true it is, but it is an interesting statement.
Another valuable article is that by N. P. Peckoff on "Quantita-
tive Light Filters for the Ultra- Violet Part of the Spectrum,"
which has appeared in the Journal of the Russian Society of
Physical Chemistry, vol. 47, pp. 918-942, 191 5.
A simple and easy test for determining the presence of the
ultra-violet light is much desired. I have worked on about nine
different tests. A well known test is to use paraphenylendiamine,
which is white, on weighted blotting paper with nitric acid and
quickly dry. This turns blue or green blue in the presence of
ultra-violet light (radiations beyond about 380/x/u), and is a very
satisfactory test because it is unaffected by ordinary light. The
amount of ultra-violet light in sunlight, by the way, with that
test is a little greater than it is with the white flame arc. As an-
2 Mott W. R., A paper read at the Sept. 1915, meeting of the American Electrochemical
Society. Use of the Flame Arc in Paint and Dye Testing.
3 Hirshberg L. K., Scientific American, vol. 112, p. 313, April 3, 1915. Review of French
work of Prof. Roux.
ULTRA-VIOLET RADIATION AND THE EYE 941
other test, lithopone, under the action of ultra-violet light, darkens
very readily and is a very good test though somewhat slow.
Dr. J. W. Schereschewsky : I think that Prof. Burge's
statements are extremely interesting and offer some very valuable
suggestions for further investigation in this interesting field. I
should like to ask Prof. Burge a few questions in regard to his
work. While it is quite possible that the ultra-violet content of
light, in the light of Prof. Burge's experiments and of the spec-
ulations of other people, might have something to do with the
production of cataract, it is rather hard to see how glass blower's
cataract can be produced by the ultra-violet component of light.
According to Prof. Burge's researches, it is evident that the active
region, so far as ultra-violet light is concerned, is rather closely
restricted to wave-lengths which are shorter than 302 millimi-
crons. It is hard to see how the light from molten glass, at the
temperature at which the furnaces are held, can produce such
ultra-violet light. At this temperature it seems to me extremely
unlikely that there would be any ultra-violet radiation from
glass furnaces of a wave-length shorter than 360 millimicrons.
I should like to ask Prof. Burge what, if any, effect was ob-
served in the eyes of fish placed in the solution of mineral salts
while they were becoming adapted to the solution? Of course, if
one goes into an aquarium there will be seen a number of fishes
which though apparently exposed only to the water, tap water or
artificial sea water as the case may be, which suffer from corneal
opacities of various kinds and often from cataracts. Now, of
course, we ought to presume, from Prof. Burge's paper, that fish
living in these mineral solutions were unaffected by those solu-
tions until they were exposed to the ultra-violet light ; but I should
like a definite statement in regard to any effects which might have
been observed in the eye apparatus of fish due to the solutions
alone. I suppose, too, that the boxes in which the fish were
placed were so narrow that it was impossible for more than one
eye of the fish to be exposed to the light. I notice that while the
photograph on the fifth page shows the spectral regions which are
most effective in producing coagulation and that undoubtedly
certain portions of the spectrum which are apparently effective in
producing coagulation of protein material, may penetrate the
942 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
cornea, we have to remember that the cornea may be somewhat
variable in its transmission. Most figures for the transmission
of the cornea show that absorption is complete of wave-lengths
shorter than 300, but there seems to be room for considerable in-
dividual variation in this respect, in that the tissues of young
animals are more permeable to ultra-violet rays than those of
older animals. Inasmuch as cataract is usually a development in
the aged, I do not know that we can always infer that the ab-
sorption of the cornea is within the limits of 300 in such cases. I
mean that in older persons it is quite conceivable that the cornea
may have become more opaque, so that the absorption, instead
of stopping at 300, may possibly extend to 305. In this way the
spectral regions shown by Mr. Burge to be especially active would
be prevented by corneal absorption from acting on the lens.
Mr. I. G. Priest: It is stated commonly that the tanning of
the human skin is due to ultra-violet light. I should like to know
whether there is a definite source for that statement and also, is
there any work which shows the cause of the difference in the
action of the light upon different individual skins? It is well
known to people who are out in the summer time that some people
tan and get a nice, leathery tan, while others repeatedly burn and
never get a tan. Has any scientific work been done on that sub-
ject?
I am interested in the question Mr. Mott raised as to whether
it is true that bacteria are not killed by ultra-violet light in the
absence of oxygen ? I can answer Mr. Mott's question by experi-
ments I have recently made myself on cotton seed oil. The color
is very permanent when exposed to direct sunlight, that is, sun-
light that comes through a thin layer of glass, if sealed in a
vacuum, while a sample of the same oil exposed to the same sun-
light, with a thicker layer of glass but in contact with the atmos-
phere, will fade in a very few hours from amber to nearly water
white. The same sample, exposed in a vacuum, in three weeks'
exposure to all the sun that would shine, showed no change in
color as followed colorimetrically on the Arons chromoscope.
On the seventh page very specific data are given in regard to
dimensions distances of lamps, etc,, but not as to the dimensions
of the box in which the fish was contained, nor as to the thickness
ULTRA-VIOLET RADIATION AND THE EYE 943
of water between the quartz window and the eye of the fish. I
should think it would be well, in revising the paper for the
Transactions, to add these data. And it seems to me rather
vague to specify water, where one is interested in the mineral
content of the water, merely as "tap water." I presume that it
was Cleveland tap water, which would be different from Wash-
ington tap water, St. Louis tap water or other tap waters.
Wouldn't it be well to supplement the statement with an analysis
of the tap water, or perhaps better to have made the experiments
in distilled water?
Dr. E. P. Hyde: It has been my privilege and pleasure to
follow the experiments of Dr. Burge throughout most of their
course. There is one point he did not mention, and I presume
that he did not, consistent with the idea which he presented that
he does not care to insist upon the explanation of various
phenomena which one encounters, on the basis of these experi-
ments, but prefers rather to let the experiments stand for them-
selves. There is one point, however, which I think of interest,
and inasmuch as it has been raised by one of the other speakers
before myself, I should like to refer to it, namely, the produc-
tion cataract in the eyes of glass workers. I had the pleasure,
some years ago, of talking with Dr. Parsons, at the time when
the Governmental Commission was being formed in England,
to consider this question. The results of the investigation in
England, as published by Professor Crooks, indicated — if I
may use the word indicated, because I scarcely think that the
data which were presented by Crooks would justify such a con-
clusion— indicated to him at least, or suggested to him, the sig-
nificance of infra-red rather than ultra-violet radiation as the
cause of the malady. One of the first experiments Dr. Burge
performed was to expose the excised eyes of pigs and cattle to
radiation of different wave-lengths. He exposed the eyes to
ultra-violet radiation, and under conditions of modified nutri-
tion, obtained cataractous lenses. He exposed the eyes to in-
tense radiation in the visible region and secured no evidence
of cataract. He placed the opening of an electric furnace at
about i,ooo° or 1,200°, very, very rich in infra-red radia-
tion, as close to an eye as he could without actually burning
944 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
the eye by the heat, and in all cases in which he was able to
keep the lens at a reasonable temperature, he obtained no in-
dication whatever of any modification which, in the presence
of the saline solutions, would produce cataract. That may be
taken for what it is worth. I do not say that this proves that
infra-red radiation may not play a part. I do not think it
proves that ultra-violet radiation is the actual cause of cataract
in the eyes of glass workers, but the fact itself is significant and
anyone may draw whatever conclusion he wants to draw from it.
From what I have heard from Dr Burge, he is not willing to
draw positive conclusions, but I think it is significant that infra-
red radiation in such quantity and intensity as he has obtained
did not produce cataract or modify the lens in any such way
that cataract was ultimately produced with the saline solutions,
and that ultra-violet radiation did modify the lens in such
a way that cataract was formed. The paper, as a whole, marks
a distinct advance in our knowledge of the effect of radiation.
Dr. H. P. Gage: Since the investigation of Crooks, every-
body interested in the manufacture of spectacles has taken a
sudden and deep interest in getting a glass which, in a thin
layer of one or two millimeters, would cut out ultra-violet rays,
and we are certainly very glad to know what radiations are
of the greatest danger; one might say fatal radiations. The
question whether radiations nearer the visible are harmful could
only be determined by very long experiment. We are also glad
to learn something of the effect of the infra-red. Apparently
the eye needs no protection from the infra-red when working
with any source except where the intensity of the light or the
infra-red is so great that there is danger of actually cooking the
tissues of the eye by the thermal effect of the infra-red, and then
it simply becomes a question of getting a glass which will cut
down the infra-red enough for comfort when working.
Mr. I. G. Priest: In regard to the suggestion just made by
Mr. Gage, I know the opinion seems to be current that there is a
cooking of the tissues. Now I do not pretend to know any-
thing about biology, but Dr. Schereschewsky is here and can per-
haps answer. Isn't that idea absurd upon the face of it? Any
amount of energy that could go into the eye could not possibly
ULTRA-VIOLET RADIATION AND THE EYE 945
raise the temperature of the lens, (as long as the subject is
living), enough to cook it. That is, would it ever get above a
fever temperature ?
Dr. ScherESCHewsky : No, I hardly think that is possible
at all. Any injurious temperature like that would certainly burn
the skin long before it could possibly affect the tissues of the
eye itself. As a matter of fact, the conjunctiva, which is very
effective in absorbing infra-red radiation, will probably not trans-
mit more than 10 per cent, of all the infra-red radiation falling
on the eye.
There was one other question Mr. Priest brought up which
I would like to mention in regard to tanning and sunburn. I
notice that Dr. Burge, in his paper, states sunburn is a form
of coagulation. I do not know whether that is so or not; but it
has been noticed, especially in the last few years, when exposure
to the sun has become a rather favorite method for improv-
ing the condition of persons suffering from tuberculosis, that
if, in the process of acquiring a good tan, excessive sunburn is
permitted, this retards very much the development of pigment
in the skin which is the result of tanning. The object of this
treatment by tanning is to improve the metabolism; that is all it
does. The aim is to cover the entire body with as deep a coat
of tan as can be secured. Certain precautions are adopted, the
exposure must be very gradual and must be only a few minutes
to start with. The entire body cannot be exposed, but only
certain portions, first the extremities and then the thorax. If
the exposure goes as far as severe sunburn, the deposition of
pigment is interfered with. Dark persons tan deeply ; very blonde
persons are almost incapable of tanning under usual circum-
stances, but by careful exposure one finds that even very blonde
persons, with a correspondingly small amount of pigment in
the skin, are capable of taking a fair amount of tan. If severe
sunburn is allowed, it so alters the protective functions of the
skin that tanning does not develop so well as when sunburn is
avoided. The protection afforded by a good coat of tan is very
marked. There are marked individual differences; some per-
sons have such good pigment production that they can stand any
amount of sunshine and it will merely intensify the deposit of
946 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
pigment in the skin. On the other hand sunshine, in others,
produces an amount of reaction which prevents good pigmenta-
tion.
Mr. I. G. Priest: Chemically, what is the difference between
sunburn and tan?
Dr. ScherEschewsky: Sunburn is a reaction of the skin to
ultra-violet rays and is quite comparable to a slight burn, where-
as tanning is a protective which consists in the deposition in
the skin of absorbing pigment.
Dr. W. R. Burge (In reply) : Only one eye was exposed and
the other was not exposed. The unexposed eye was the control.
So far as the objections to the carrying out of our experiments on
living animals in tap water is concerned, and the suggestion that
we should have used distilled water, it is known that living pro-
toplasm is killed by distilled water. I think that Dreyer and
Hansen exposed many substances to the radiation from a quartz
mercury-vapor burner. In Parke-Davis' laboratory the work
has taken up during the last year or two and many more addi-
tional substances have been exposed to the radiation from a
quartz mercury burner. So far as glass blower's cataract is con-
cerned, I do not wish to say anything about the application of
this work or whether it may be applied or not. I think such
discussion would be futile, and all that can be done is to take the
experiments for what they are worth. If the experiments have
any practical value it is to be hoped that such application may
be made in due time. So far as the experiments on the tanning
of the skin are concerned, these were incidental. Anyone can
perform the experiment for himself, if, before going out to row,
he wets one side and leaves the other dry. It will be found that
the wet side always sunburns much more quickly than the dry
side. The salt in solution on evaporation of the water on the
skin, becomes more concentrated, and acts as the salt in these
experiments. I don't know of any data on the subject.
Mr. Priest: Was your experiment made with salt water or
fresh water.
Dr. Burge: Fresh water from Lake Erie.
MEES: ARTIFICIAL IELUMINANTS 947
ARTIFICIAL ILLUMINANTS FOR USE IN
PRACTICAL PHOTOGRAPHY.*
BY C. E. KENNETH MEES.
Synopsis: Artificial illuminants can be used in negative making for
portraiture, cinematograph work and photo-engraving. For portraiture
diffused sources are necessary, and either a large source must be used or
the light must be reflected from a large area. In cinematograph work
about a quarter kilowatt per square foot of stage is used, the usual
arrangement including the use of mercury-vapor lamps overhead and at
one side of the stage, and arcs in front. For photo-engraving an arc lamp
is hung on each side of the copy board, most engravers using flame carbon
arcs.
For printing papers the enclosed arc is used for silver papers while
for platinum the mercury-vapor lamp is satisfactory. In printing fish glue
on metal it is important that a small source of light should be used in
order to get sharp definition of the dots, and the printing should be as
far away as possible. The photographic efficiency of artificial illuminants
depends upon their quality and upon their visual efficiency, but must be
considered from the point of view of the materials used, which materials
are of three chief kinds: (1) panchromatic materials sensitive to the
whole spectrum and used with filters to give a rendering similar to that
seen by the eye, or for color photography; (2) ordinary materials having
their maximum sensitiveness in the blue violet; (3) materials sensitive
only to the ultra-violet. For panchromatic materials the efficiency of the
illuminant will depend almost entirely upon its visual efficiency, while for
ordinary materials the chief point of importance is the efficiency in the
blue violet, but since the latitude and freedom from halation increase
with shorter wave-lengths it is better to use light sources having their
maximum near 400/"/"' rather than near 470MM. It is pointed out that nearly
all artificial illuminants have application in some branch of photography
or other.
While in the early days of photography almost the only source
of light was the sun, the application of artificial illuminants to
the art is continually increasing. The illuminants which are
available are of many kinds, and, indeed, include all the more
powerful sources of light. The advantages of artificial illum-
inants which have caused their introduction are chiefly their
constancy and their ready availability ; the variation of the inten-
sity of natural light makes the judging of the time for which the
sensitive material is exposed a difficult task, so that the photog-
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, '91 5-
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
Communication No. 31 from the Research laboratory of the Eastman Kodak Com-
pany.
948 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
rapher has to acquire considerable skill and experience in order to
avoid obtaining results showing the effect of incorrect exposure,
while with most artificial illuminants the matter of exposing can
be reduced to a simple calculation of time, thus eliminating one
chance of insuccess. The possibility of working at any time
under evenly uniform conditions is certainly an advantage in such
divisions of photography as photo-engraving, trade enlarging and,
indeed, all commercial work ; while it is a further advantage that
the artificial sources of light are available whenever they are re-
quired and that the worker is not confined to a small portion of
the day or to an intensity dependent on meteorological conditions.
One may summarize the purpose for which artificial illumi-
nants are used and the properties required in the illuminant when
it is applied to a particular purpose somewhat as follows :
Negative Making: Portraiture. — For portraiture a large dif-
fused light source is a necessity in most work and only occasion-
ally can a concentrated source be used. Consequently, either a
very extended source such as that given by the mercury-vapor
lamp must be employed, or else a completely diffusing system is
arranged; thus, for an arc it is convenient to place the reflector
behind the arc so that the light is directed away from the sitter on
to a large secondary reflector, which may be a wall, though it is
usually more convenient to have a movable arrangement. What-
ever system is used for obtaining a large source of diffused light
curtains and screens are necessary so that the operator can adjust
the area and direction of the light at will. An arrangement which
has given satisfaction consists of a battery of 12 or 16 nitrogen
tungsten lamps placed in a frame behind a diffusing medium and
covering an area of 30 or 40 sq. ft., the area to be utilized being
modified by applying independent control to the separate lamps.
Cinematograph Work. — In moving picture studios a consider-
able amount of light is necessary owing to the speed at which the
pictures are taken, the exposure being only 1/40 of a second with
an aperture of about F/8. The average stage, including an area
of perhaps 240 sq. ft., requires about 60 kilowatts for illumination,
and a typical arrangement of the lights will consist of 40 to 50
kilowatts expended in mercury-vapor lamps or quartz arcs ar-
ranged about 12 to 15 ft. above, as a roof to the stage and down
MEES: ARTIFICIAL ILLUMINANTS 949
one side to a distance of about 3 ft. from the floor, and about
12 kilowatts used in some form of arc, conveniently a flame arc,
about 10 ft. in front of the stage and the same distance from the
floor ; such an arrangement is typical of many of the stages used
by the large producers of moving pictures in this country and the
importance of artificial illumination in this work can be realized
when it is understood that many producers will have six such
stages working at a time.
Photo-Engraving. In photo-engraving the copy-board is gen-
erally lighted by an arc lamp hung on each side. In the earlier
days these were usually open arcs and later, especially in Europe,
the enclosed long flame carbon arc came into use, and is still very
convenient for work with wet collodion, but it is unsuitable for
color work owing to the deficiency of red and especially of green
light. In this country many photo-engravers use open arcs with
white flame carbons, which appear to be quite satisfactory. The
quartz lamp would be suitable for black and white work if it came
up to efficiency in less time, but a great lag in reaching efficiency is
against it. Neither the quartz lamp nor the mercury-vapor lamp
seems to be as efficient as the flame or enclosed arcs; for color
work the nitrogen tungsten lamp might perhaps be applied to ad-
vantage.
For color photography, such for example as color portraiture,
the most important thing about a lighting system is the constancy
of the quality of the light ; but high intensity is required and the
conditions as to size of source already explained under portraiture
fully apply: we have adopted the battery of nitrogen tungsten
lamps already spoken of as being very suitable for color por-
traiture.
In ordinary photographic printing the Aristotype and solio
papers which used to be very popular are often printed by means
of a large enclosed arc instead of daylight, and this seems to be
very suitable for the printing of such silver papers. For platinum
printing, however, it is advisable to use a source of light which is
not so hot, as the heat is very liable to give mealy prints. One
large company do their trade printing by means of mercury- vapor
lamps which are held constant by a resistance and ammeter, the
current being watched and the printing being done entirely by time.
950 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Bromide and chloride papers are, of course, printed by artificial
light exclusively, the usual printing cabinet containing tungsten
lamps, though for quick trade work an arc lamp or mercury-vapor
lamp is frequently used, thus enabling very short exposures to be
given.
For enlarging it has been customary to use an open arc, but if
a condenser is used, it would seem to be better to employ a con-
densed filament tungsten lamp because of its great constancy, the
changes in the intensity of an arc making accurate exposure diffi-
cult unless the arc is one which permits of very good regulation.
Much enlarging in trade houses is done without a condenser, the
negative being lighted by a diffusing screen behind which the
source is placed, such a suitable diffusing screen being a sheet of
opal glass. For such work suitable illuminants are the enclosed
flame or open white flame arcs, but if mercury-vapor lamps are
used, a powerful diffuser is not needed, a sheet of ground glass
being sufficient if the tubes of the lamp are arranged so that there
are a number parallel to each other a short distance apart.
For the printing of fish glue or a similar resist on metal in
photo-engraving it is important to have a small source of light in
order to get sharp dots, as otherwise a very high pressure is re-
quired to ensure sufficiently good contact ; and it is, indeed, almost
impossible to print dry plates made on ordinary sheet glass by
means of large sources of light. The arc must necessarily be
powerful, but the flame should be as small as possible and the
distance as great as can be used in order to prevent the exposure
being too long. It would appear that for metal printing there is
an opening for the development of some form of lamp in which
approximately parallel light of high intensity is obtained.
For some photographic purposes constancy and lack of flicker
are essential, average constancy being important in almost all pho-
tographic operations. Flickering is a less serious disadvantage
in many operations than lack of average constancy, but where the
exposure is short, as in developing out printing, enlarging or
photo-engraving, flickering of the light source is very much to be
deprecated, and this is a great disadvantage of enclosed and open
arcs. The table on the fifth page summarizes the advantages and
disadvantages of various illuminants for different classes of work,
MEES: ARTIFICIAL ILLUMINANTS
951
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952 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
the efficiency, which is considered in the next section, being also
taken into account.
In addition to the suitability of a light source as to size, con-
stancy, intensity, etc., the efficiency and quality of the light must
be considered. The visual efficiency and the quality taken to-
gether will represent the photographic efficiency, since this can
be calculated if one knows the spectral energy curve, which is the
quality, and the height of one portion of it which is given by the
visual efficiency. This relation between the visual and photo-
graphic efficiency for a number of light sources and for three
different classes of photographic materials has been dealt with by
Messrs. Jones, Hodgson and Huse in their paper* presented to
this meeting.
When we consider the quality and efficiency of an artificial
illuminant for use in photography we are confronted with a
problem of rather different type from that with which we meet
when the illuminant is for visual use. The color sensitiveness of
the human eye in different individuals is so nearly alike that we
need consider only the visibility curve of the average human eye,
which can be determined with sufficient accuracy by taking the
mean of the curves obtained by a number of observers, after-
wards rejecting any results where the sensibility is not approx-
imately the same as that of the average as being abnormal or
pathological cases which can be ignored in the general choice of
an illuminant ; but there is no such average sensitiveness in photo-
graphic materials. In dealing with the choice of an illuminant
for photographic purposes we must consider the use to which it
is to be put and the materials which are likely to be exposed by
means of it.
There are three main groups of photographic materials as re-
gards their spectral sensitiveness : ( i ) materials which have been
sensitized by means of dyes to the longer wave lengths of the
spectrum and which are intended for use with color filters either
to obtain a rendering approximating to that perceived by the
human eye or for use in color photography where exposures are
made for two or more defined areas of the spectrum. These
materials are usually known as "panchromatic." Panchromatic
plates are sensitive to the whole visible spectrum, their sensitive-
* Published in this number of the Transactions.
MEES: ARTIFICIAL ILLUMINANTS 953
ness between Asoo^/x and A6oo/i/i being about one eighth, and be-
tween A6oo/x and A800/A about one-tenth of their total sensitive-
ness to daylight. (2) Positive or negative materials sensitive only
to the blue violet and ultra-violet regions of the spectrum, and
with their maximum sensibility in the blue-violet region, these
including all ordinary plates or films used for landscape or por-
traiture, dry plates used in photo-engraving, and all the printing
materials which are developed, such as bromide or gas light
papers. These materials have a sensitiveness extending from the
ultra-violet to about A500/1M, the sensitiveness diminishing rap-
idly with longer wave length after about M6ow*- (3) Materials
which are sensitive almost exclusively to the ultra-violet, such as
printing out papers or the wet collodion plates used in photo-
engraving.
These classes of materials do not coincide with those discussed
by Messrs. Jones, Hodgson and Huse; their "ordinary" materials
are my second class materials sensitive only to the blue and ultra-
violet regions, and their panchromatic or orthochromatic materials
are considered, as they explain, as being used without filters and
therefore do not coincide with my first class, where the materials
are considered as being used only with filters, because in practise
color sensitive materials are almost always used with filters which
correct the light affecting the plate so that the plate sensibility
and the spectral energy curve of the light and the filter together
produce a rendering comparable with that observed by the eye by
daylight. A light source is therefore more efficient with these
materials if it enables us to make use of a weaker filter to attain
the same result.
For panchromatic materials the efficiency of an illuminant de-
pends chiefly on its visual efficiency, since it is used under such
conditions that the light affecting the materials is nearly the
same as that to which the eye is sensitive. Any ultra-violet light
is of no use whatever, since it must be cut out by the filters, but
inasmuch as the most color-sensitive materials which can be made
are still deficient in their red sensitiveness compared with their
sensitiveness to the green or blue, it is advisable that the maxi-
mum energy of the light source should be shifted towards the red
end of the spectrum as compared with daylight; in fact, the high-
954 TRANSACTIONS OF IEEUMINATING ENGINEERING SOCIETY
est efficiency will be realized with a quality of light where the
energy maximum is about A6oo/*/ji, and any source approximating
this, provided its spectrum is continuous or nearly continuous,
will be of suitable quality, the decision as to which illuminant
is to be used resting chiefly on the question of its visual efficiency
and its suitability in other respects, such as area and steadiness.
The "ordinary" materials, which comprise by far the greater
quantity of all photographic materials used, require a source of
light of which the maximum is in the blue violet and, indeed, the
energy maximum of these materials is between \380n1x and \460n11,
varying somewhat from one material to another but having
X440fi/j. as a fair average for the maximum of the negative mater-
ials of this group. The photographic efficiency, therefore, of a
light for use in ordinary negative making depends upon its in-
tensity around A440/UJU.
Another question than efficiency, however, enters into the choice
of a light for negative making; the latitude of the photographic
emulsion varies very rapidly with its absorption, and the scale,
gradation, and latitude of photographic materials depend upon
the wave-length of the light to which they are exposed, since the
absorption varies greatly with the wave-length, the scale being
greater the shorter the wave-length. Other things being equal,
a negative taken by light of A48o/u,/u, will have a shorter and steeper
scale and less perfect gradation than if it were taken by light of
A400/X/*.
Halation is caused by the penetration of light through the
emulsion and its reflection from the back of the support, there
being more halation the longer the mean wave-length of the il-
luminant employed, since the emulsion is more transparent the
lower the frequency of the light. Where halation is a difficulty,
therefore, as, for instance, in portraiture or cinematographic
work, it is desirable to use an illuminant where the photographic
effect is largely in the ultra-violet rather than one which depends
upon the longer wave-length end of the blue violet for its effect.
It is an advantage, therefore, both for the attaining of the best
gradation and for the reduction of halation to a minimum to use
for these ordinary materials light of an average wave-length as
near as possible to A400/i|u. rather than light having its maximum
near X^yofifi.
MEES: ARTIFICIAL IU.UMINANTS
955
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956 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
The third class of materials, sensitive only to the ultra-violet,
naturally require illuminants producing as much ultra-violet as
possible, and the efficiency of the illuminant depends largely upon
the intensity of the ultra-violet light which can get through
glass, because it must be remembered that the ultra-violet light
which cannot penetrate glass is of no use in photography, where
the lenses or negative supports will cut out all rays below A330JU/A.
It may be mentioned that carbon tissue, photogravure tissue,
bichromated fish glue and, in fact, all the materials which depend
on the sensitiveness of bichromate are more sensitive in the blue-
violet than in the ultra-violet, the maximum sensitiveness of
these materials being near A460/X/X.
The table on the ninth page summarizes the various qualities of
the chief artificial illuminants. The figures for visual and photo-
graphic efficiency are from the paper by Messrs. Jones, Hodgson
and Huse, 100 being taken as the efficiency of sunlight.
It will be seen that almost all sources of artificial illumination
have application in some branch or other to photography. Each
source has its own particular sphere of application, and no one
source is suitable for all purposes. Claims are often made on
behalf of one or other method of producing light as being the
ideal source for all purposes, but such exaggerated claims only
do harm to the cause which they are intended to advance, and it
is better to recognize that photography is a wide field, having
many sub-divisions, and that nearly all sources of light can be
applied with special advantage in some one or other of those
divisions.
DISCUSSION.
Mr. M. Luckiesh : My side of this subject involving the de-
velopment of a photographic tungsten lamp and the general appli-
cation of the tungsten lamp to photography was presented before
this Society in January (Trans. I. E. S., vol. X, No. 2, p. 149,
1915), and I believe Dr. Mees is in general agreement with the
conclusions presented in that paper. It is very difficult and I
believe inadvisable to attempt to draw sweeping conclusions in
dealing with such a subject as photographic illuminants, and I
am glad to hear Dr. Mees qualify some of his conclusions while
presenting his paper.
ARTIFICIAL IU/UMINANTS 957
With the recent increase in the efficiency of tungsten lamps,
there appeared the first important opportunity for the tungsten
lamp to enter the photographic field, therefore we made an exten-
sive study of the subject in relation to the tungsten lamp. This
brought us into the practical application of our developments and
we have long ago realized that in portraiture (the chief field at
which we aimed) the personal opinions of photographers dif-
fered so that no general decisions as Dr. Mees attempts to give
in his tables are worth much. If the author of this paper repre-
sented the composite portrait photographer his conclusion would
be of considerable interest but very likely such is not the case
because opinions are so varied.
The tungsten lamp at present can not be introduced into all
photographic fields. It is operating at present with considerable
success in portraiture, color photography, printing, enlarging,
copying, and to some extent in moving-picture production. The
principal development has been in the blue-bulb photographic
tungsten lamp which emits a light that approximately matches
daylight in color and by absorbing some of the rays that do not
affect ordinary plates a light of high actinic value per lumen is
obtained. The actinic value per lumen is roughly the same as
daylight with the result that short exposures without glare can
be obtained in portraiture. The actinic value and color of the
light approaching closely to that of daylight, makes it possible to
use this illuminant in combination with daylight. This has been
a desirable feature in many cases. The success of the unit has
been demonstrated by thousands of practical installations and
demonstrators of a large photographic supply house are com-
pletely equipped with them. Opinions of noted portrait photo-
graphers are much more valuable than such a summary as is
given in this paper by one who in presenting the paper stated
that he could not qualify as portrait photographer or as an expert
in most of the fields considered. Such a unit as the photographic
tungsten lamp has an additional feature of merit namely the ease
of control by rheostats or reactances. As I have stated on several
occasions the lamps operate satisfactorily at normal voltage but
inasmuch as photographic conditions are so different from or-
dinary lighting conditions, it is justifiable to operate these lamps
considerably above normal voltage thereby taking advantage of a
958 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
tremendous gain in actinic value. Dr. Mees' data and conclusions
are no doubt based upon normal operating voltage. They would
have been still more favorable to the tungsten lamp if based on
a voltage above normal which is justifiable.
Dr. Mees stated that in the moving-picture studio the aperture
at which pictures are taken is F8. Several producers have stated
to me that F5.6 is the maximum aperture necessary for indoor
work and that on many sets F4.5 is used indoors.
The clear tungsten lamp has been found successful in color
photography but Dr. Mees fails to give the blue-bulb photographic
tungsten lamp any mark in this column. Apparently he believes
it has no continuous spectrum because any illuminant having a
continuous spectrum is at least "very poor" for color photo-
graphy. Color photography is at present a very crude process
yielding far from perfect results. I have found that the blue-
bulb lamp yields practically the same results as daylight even
when the same filters are used. Of course it is wasteful to
throw away light that is photographically active and we would
not recommend the blue-bulb lamp for general adoption in color
photography. However, these are studios in which some work is
done along this line. If these studios are equipped with blue-bulb
photographic lamps for portraiture I wish to assure the operators
that they can use these lamps very successfully for color-photo-
graphy. Quite the same argument holds for enlarging. Dr.
Mees fails to give a mark to the blue-bulb photographic lamp in
this column which is again misleading.
One great advantage of a portable unit such as the tungsten
photographic lamp is that it can be placed in any position. This is
a dominating feature in portraiture after actinic value has passed
the test. Dr. Mees does not lay any stress upon this point, but
an acquaintance with a few hundred studios equipped with such
a unit would convince him that there are many features to be
considered in making out tables such as he has attempted.
Inasmuch as I have gone into detail on this subject on several
occasions, I will not discuss it further but will conclude by stating
that Dr. Mees has presented a personal opinion in this paper
which loses weight inasmuch as he stated in introducing his
paper that he could not qualify as an expert in many of the fields
ARTIFICIAL ILLUMINANTS 959
which he discussed. After all the conclusions of those who use
illuminants daily in various photographic fields will determine the
future of photographic illuminants.
Mr. W. R. Mott: Dr. Mees' paper represents a very broad
subject and one that deals with an enormous variety of processes.
I admire very much his sound and careful treatment of the whole
subject and I agree with him in nearly all respects. While ad-
mitting the superior efficiency of the flame arc, he has suggested
some of the objections to the flame arc, namely, that of fumes,
odor and the question of its being a concentrated source of light.
With regard to fumes and odor, these can be taken care of by
placing a little ammonium carbonate in a cabinet with a diffusing
screen. Such a cabinet was exhibited two years ago before two
hundred photographers and no one complained in the least of
odor, although it was running (nearly continuously) during the
four days. The construction of such a cabinet may be described
as about 5 feet across, 7 feet high and 3 feet deep. It is arranged
with the curtain at a 45 ° inclination both vertically and on the
side so that a perpendicular from the center of the curtain enters
the field where maximum illumination is desired. Such a cabinet
(with white flame arc) has been in satisfactory commercial oper-
ation in a portrait studio for over five years in Cleveland. Since
then others have been using the flame arc on quite an extensive
scale.
Since, other things being equal, the test comes on the question
of efficiency, I wish to call attention to the fact that the flame
arc is ahead of all the other sources of light for efficiency in
the high amperage arcs. This is shown in the following tables.
Line volts Arc volts Amperes
White flame arc (open) 115 63 28.0
Nitrogen lamp, clear globe ... . 117 117 6.7
Nitrogen lamp, blue globe 115 115 8.5
The gas-filled incandescent lamp with a blue bulb taking 8.5
amperes gave 485 mean spherical candlepower. The candlepower
for the 28 ampere flame arc was 5130. (For equal line wattage
the flame arc gave over three times the candlepower.) The candle-
power efficiency is not only much in favor of the white flame
arc, but also there is the quality of the light which is an almost
Mean
candle-
Spherical
photo.
power
power
5.I30
IOO
866
4
485
5
960 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
exact duplicate of sunlight plus blue sky. This means that the
light is bluer than that of the lamp with a blue glass bulb (and
because of the higher content of blue, violet and ultra-violet),
and the light is photographically more efficient.
Dr. MEES : What was the material ?
Mr. Mott: Solio paper.
Dr. Mees : That is the most disadvantageous paper one could
select; it is only sensitive to ultra-violet light.
Mr. Mott : I tested it through glass and found that the ultra-
violet light of the white flame arc was nearly the same in amount
and quality as in sunlight plus blue sky.
A Member: Might I add that these tests were made for wet
plates.
Mr. Mott: In regard to other photo-chemical reactions, as
in dye fading, I have found that the time required with a 750-
watt clear glass gas-filled incandescent lamp was 17 to 100 times
longer at equal distances than with the white flame arc at 28
amperes on 115 line voltage.
I write these figures here in the tabe for comparison. Then,
in addition to these factors (candlepower, quality of light,
and dye fading tests) we must remember that the flame
arc is capable of enormous improvement, and I would say that
it is possible with known processes, by combining them all to-
gether to increase the efficiency not 100 per cent, but 300 per cent.
In further examination of these efficiencies, I might say that a
test was made by Lux, in which he showed that a gas-filled
tungsten lamp using 495 volts had an effect photographically of
8850; while that of a 220 volt enclosed arc lamp of 9.3 amperes
had a value of 243,000. The quartz mercury arc had a rather
considerable change in photographic value with change in cur-
rent, and after a certain amperage decreased in photographic in-
tensity.
A paper, "The Commercial Light Sources in Photography," by
Dr. H. Lux, Blectrotechnische Zeitschrift, pages 203, 204, April
29, 191 5, and Sheppard's book on Photochemistry, page 102, give
some interesting data on the photographic power of various light
sources.
ARTIFICIAL ILLUMINANTS 961
The enclosed arc lamp on no volts at 28 amperes is not as
efficient for action on solio paper or blue print paper as the flame
arc at the same amperage. My tests on blue printing and on
solio papers show two and a half to three times greater speeds
for like line power. (On 220 volts, two to four high amperage
flame arcs are used in series.) The important consideration is
that the white flame arc on no volts is much more efficient than
the efficient enclosed arc of high amperage. (Many photographic
operators use flame carbons even under semi-enclosed arc con-
ditions.)
Dr. C. E. K. Mees (In reply) : I would like the opportunity
of just replying to the criticism with regard to the lens aperture
in the cinematograph studios. I am sorry Mr. Luckiesh was
misled, and only wish you could see an aperture of 4.5 in the
studios; I shouldn't have any trouble whatever with sensitive
materials. There is not enough depth on the stage in the focal
plane to use such an aperture as 4.5. You can use it when you
are working with your actors sitting down at a table, but when
they chase each other over the stage and fall down stairs, it
doesn't work. With regard to windows in studios, and the sug-
gestion that they be made smaller and put nearer — that is satis-
factory where one sitter is to be photographed; but studios are
usually designed to take groups of not less than six people ; so I
think you must be prepared to make, for good workers and large
studios, quite considerable windows. The artist himself will cut
that window down ruthlessly with blinds, but you cannot help that.
With regard to Mr. Mott's point — I only referred to the fumes
and odor of the flame arc when used for color photography.
When a single lamp is used, there is no difficulty, but in color
work you have to use an enormous number of lamps and it
is quite a difficult problem to handle the fumes from the flame
arc. I would like to make a suggestion to Mr. Mott, and I know
he will take it as being from a neutral. He has published these
figures before, and they created on me a very unfavorable im-
pression. If an illuminating engineer wants to give figures, I
think he ought to give them in watts per spherical candle.
As to comparisons on solio paper, that would be satisfactory if
962 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
it were stated that it was for the purpose of wet plates but not
for ordinary photographic work. It is most important, when
you have a perfectly good case, as Mr. Mott has on photographic
efficiency, that you should make the most of the other fellow's
case.
JONES, HODGSON, HUSE : EFFICIENCIES OE ILLUMINANTS 963
RELATIVE PHOTOGRAPHIC AND VISUAL EFFICIEN-
CIES OF ILLUMINANTS.*
BY L. A. JONES, M. B. HODGSON AND KENNETH HUSE.
CONTENTS.
PAGE
I. Introduction • 964
II. Method 965
III. Apparatus • 9^7
a. Sensitometer.
b. Photometer.
c. Densitometer.
IV. Photographic Materials 969
a. Ordinary.
b. Orthochromatic.
c. Panchromatic.
V. Sources ••• 97°
a. Sun 97o
b. Sky 97o
c. Acetylene 971
d. Screened acetylene 971
e. Pentane 971
f. Mercury arc, quartz tube 971
g. Carbon arc, open 971
h. Carbon arc, white flame carbons 971
i. Carbon arc, enclosed, short arc 972
/. Aristo arc, enclosed, long arc 972
k. Magnetite arc • 972
/. Carbon incandescent 972
m. Tungsten, vacuum 972
n. Tungsten, gas-filled 972
0. Tungsten, gas-filled, blue bulb 972
p. Mercury-vapor 972
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
Communication No. 30 from the Reasearch laboratory of the Eastman Kodak Co.
964 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
PAGE
VI. Experimental details and errors 972
VII. Results 974
Typical curves and data ... 970b, 975
Efficiency curves 97ob, 975
a. Carbon incandescent 970b
b. Tungsten, evacuated 975
c. Tungsten, gas-filled 975
d. Tungsten, gas-filled, blue bulb 975
Efficiency tables 977
INTRODUCTION.
It is well known that, of two light sources which measured
visually are of equal intensity, one may produce a much greater
effect on a photographic plate than the other. This is due to the
fact that the spectral sensibility curve of the photographic plate
differs greatly in shape and position from that of the retina. The
maximum of the visibility curve lies at 555/t/*, while the maxi-
mum of the spectral sensibility curve of an ordinary plate lies in
the blue-violet region at approximately 460^/x. Hence, if we have
two sources of equal visual intensity, one being bluish and the
other yellowish in color, the blue source will produce the greater
effect on the photographic plate. For these reasons it is not
possible by a measurement of visual efficiency to decide upon the
effectiveness of a source for photographic work; that is to say,
the photographic efficiency is not proportional to the visual
efficiency.
A further complication arises from the fact that different types
of photographic materials have very different spectral sensibili-
ties, ordinary plates being sensitive only to blue, while ortho-
chromatic plates are sensitive to blue and yellow-green, and pan-
chromatic to blue, green and red. The problem presented, there-
fore, is the determination of the relation existing between the
visual and photographic efficiencies of various illuminants when
used in connection with photographic materials having certain
typical spectral sensibilities. In this paper the work is confined
to high speed materials used for negative making, no attempt
being made to cover the entire field of photographic sensitive
materials.
JONES, HODGSON, HUSE : EFFICIENCIES OF ILLUMINANTS 965
METHOD.
The method adopted for obtaining the desired ratios is essen-
tially that used in the determination of plate speeds, and is briefly
outlined in the following paragraphs.
If a strip of the plate to be tested be exposed in such a way
that successive areas receive exposures increasing by consecutive
powers of 2, it will be found upon development that a series of
spots of increasing opacity are obtained. By measuring the
density of each of these spots and plotting the value obtained
against the logarithms of the exposures given, a curve is obtained
which is known as the characteristic curve of the plate. Such a
curve is shown in Fig. I.
The term "density" as used in this work is defined as follows :
Let T = Transmission
Then 7p = Opacity, O
and log O = Density, D. D = — log T.
It will be noted by reference to Fig. 1 that the portion of the
characteristic curve between A and B is a straight line. This
line extended cuts the log exposure axis at O, and the value of
the exposure at the point O is termed the "inertia" of the plate.
This "inertia" value is proportional to the insensitiveness of the
plate, and the reciprocal of the inertia is proportional to the sen-
sitiveness or speed of the plate. Speed numbers for a plate are
obtained by multiplying the reciprocal of the inertia by some
arbitrarily chosen constant. The inertia value obtained does not
in general depend upon the time of development or upon the con-
stitution, concentration, or temperature of the developer used.
In Fig. 1, curve a was plotted from a strip developed three min-
utes, and curve b from one developed six minutes. It will be
noted that the straight line portion of each curve cuts the log E
axis at the same point, showing that the inertia value is inde-
pendent of the time of development.
The value of the inertia, however, does depend upon the quality
of the light to which the plate is exposed. Thus, if the plate is
sensitive to blue light only, a lower inertia (higher speed number)
will be obtained when a bluish light is used than when one of
yellowish color is employed. Hence, for a standard source for
966 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
use in sensitometry it is necessary to specify not only the intensity
but also the quality of the light emitted. The fact that the inertia
value obtained depends upon the quality of the light to which the
plate is exposed offers a very convenient means of measuring
the relative photographic efficiencies of different illuminants.
In testing plates for speed the light source is kept constant in
quality and intensity, and the reciprocal of the inertia value
obtained is proportional to the speed of the plate. Now, if the
plate speed be kept constant and the quality of the light changed
by using different sources, the reciprocals of the resulting inertia
values may be taken as directly proportional to the relative
photographic efficiencies of the various sources.
/
/^
/
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LOG EXPOSURE
Fig. 1.
Suppose that using source A an inertia value of ix is obtained,
and with another source B the inertia is i2. Then the photo-
graphic efficiency of B relative to that of A will be — X 100.
h
Obviously, in making such a comparison it is necessary to choose
some source to be used as a standard. Since in practical work a
great majority of the plates used are exposed to light from the
sun, it seems most logical to adopt that as the standard of quality
by which to judge all artificial illuminants. Some may contend
that daylight or north skylight would be more suitable and
JONES, HODGSON, HUSE : EFFICIENCIES OF ILLUMINANTS 967
nearer to actual practise as a standard of quality. Daylight is a
mixture of sunlight and skylight in some indefinite and variable
proportion, and skylight is likewise indefinite in quality and not
reproducible. Sunlight, on the other hand, if taken between
9 a. m. and 3 p. m. on a clear day, is of a very definite quality.
For these reasons sunlight has been chosen as a standard of
quality, and its photographic efficiency on any plate is taken to
be 100 per cent.
APPARATUS.
The sensitometer used in this work is of the "falling plate" type.
An aluminum plate in which a series of openings of varying
lengths are cut moves up and down between a pair of ways. This
plate is driven at a very uniform rate by a constant-speed gov-
erned motor. The openings in the plate increase in length by
powers of \/l so that a sensitive plate placed behind it in a suit-
able dark slide will receive a series of exposures increasing by
consecutive powers of T/T; thus, twice as many points are ob-
tained as in the usual type of sensitometer, allowing the charac-
teristic curve to be more precisely located and, hence, the inertia
value more definitely determined. The rate at which the falling
plate moves is very constant and is so precisely known that the
time of exposure can be determined to within ±0.2 per cent.
In order to measure the illumination on the photographic plate
a means is provided by which a modified Lummer-Brodhun pho-
tometer head may be inserted in place of the dark slide, the pho-
tometer screen occupying the same plane as the photographic
plate when in position for exposure. One side of the photometer
screen is illuminated by a small electric glow lamp carefully
seasoned and controlled to constant current by potentiometer
method. This lamp is mounted on a small carriage moving on a
pair of rails, with scale and index. The scale was calibrated by
means of a standard glow lamp set at varying distances from
the other side of the photometer screen. Thus it is possible to
measure very accurately the illumination incident on the photo-
graphic plate.
The sensitometer is mounted on a pair of rails running along
the top of a table extending down the side of the photometer
room. At one end of this table is the photometer bench on which
9
968 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
is mounted a three meter photometer of the National Physical
Laboratory type. The rails carrying the sensitometer are lined
up in such a way that as the instrument is moved along the ways,
the plate holder containing the plate to be exposed remains
always on the photometric axis of the bench photometer. The
light source to be tested is mounted on the photometer and by
moving the sensitometer along the rails the distance between the
plate and source can be adjusted, as desired, to any value up to
twelve meters.
The sensitometer is provided with a set of gears so that the
falling plate can be driven at various velocities. The highest
velocity of movement gives an exposure of two and one-half min-
utes to that portion of the plate behind the longest slot. It was
found that for medium speed plates and with the machine run-
ning at its highest velocity that an illumination of 0.1 meter
candle on the plate gave the proper exposure for the production
of a complete characteristic curve. Hence, an illumination of 0.1
meter candle was adopted as standard.
The distance available (12 meters) is only sufficient to make
possible the use of sources running up to an intensity of 14.4
candlepower ; therefore, in order to test high candlepower sources
such as the 1,000- watt gas-filled lamps, it was necessary to devise
some means of reducing their intensity without altering the
quality of the light. A rotating sector cannot be used on account
of the danger of introducing errors due to the intermittency of
the exposure given to the photographic plate. Various absorb-
ing and diffusing screens were tried but none were found suffi-
ciently non-selective to permit of their being used in work of
this kind. Finally, a lens system was tried and found to be very
satisfactory for the purpose.
Two lenses of short focal length are mounted so as to move
along the photometric axis. The one nearest to the source is so
placed that an image of the source is formed at the principle
point of the other lens — the one nearest to the sensitometer.
This arrangement gives a very uniformly illuminated field, readily
adjustable to any intensity by varying either the focal lengths of
the lenses used or the distance from the source to the first lens.
The lenses used for this purpose are made either of a clear
a
ORDINAE-Y
mil-1 j • iiiiiiiiiiiiii1111111111""11'111
ORTHO -CHROMATIC
PANCHROMATIC
Fig. 2.— Spectral sensibilities of photographic materials.
r
a l
UMENS
= 2 3£
WATT
b-
c-
;
= &.S5
= 150
i
-b
%
f//
/y>/
/ / //
4f.
4f/
LOG EXPOSURE
Fig- 3-
Fig. 4.
JONES, HODGSON, HUSE : EFFICIENCIES OF IELUMINANTS 969
white crown glass or of quartz. All reduction of intensity, then,
is made either by increasing the distance or by use of lenses, and
thus any change in the quality of the light is avoided. Since
the sensitometer is of the falling plate type the exposures are
always continuous, and all danger of intermittency errors is
avoided.
The photometric measurements were made on the bench pho-
tometer. The head is of the ordinary Lummer-Brodhun type and
the standards used are certified by the Bureau of Standards and
by the National Physical Laboratory. These standards were
operated on a storage battery and controlled by the potentiometer
method. The electric sources used were operated, when possible,
from the storage cells and controlled by potentiometer or by
reliable Weston volt and ammeters. Measurements involving a
difference in color were made directly without the aid of
compensating filters or a flicker photometer. Readings were
made by two experienced observers, and errors occurring due to
a lack of color match are undoubtedly much less than those due
to other factors involved in the sensitometric measurements.
The measurements of density were made by means of a Mar-
tens polarization photometer, the plates being placed with the
emulsion side in contact with an opal glass diffusing screen so
that the values obtained were for the diffuse density of the
deposit.
PHOTOGRAPHIC MATERIALS.
Photographic materials used for negative making, classified
with respect to the spectral sensibility, fall into three distinct
groups ; ordinary, orthochromatic and panchromatic.
The first of these, the ordinary, is sensitive only to violet, blue
and blue-green, the maximum occurring at about 460/uft. This
is shown by the photograph reproduced in Fig. 2, which is a
spectrum photograph made on an ordinary plate (Seed 23) by
exposure to an acetylene flame. The photograph was made in
a grating spectrograph in front of the slit of which was placed a
neutral gray wedge, thus causing the intensity to decrease
logarithmically from one end of the slit to the other. The curve
outlined by the dark portion is, therefore, the resultant of the
970 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
spectral sensibility curve of the plate and the spectral energy
curve of the source — in this case an acetylene flame.
Materials of the second class, orthochromatic, are sensitive to
blue and yellow-green, as is shown in Fig. 2, this being a spectrum
photograph made on an orthochromatic plate. In this case a
second maximum occurs in the yellow-green at about 560^.
The third class of materials, panchromatic, is sensitive to prac-
tically the entire visible spectrum; Fig. 2 shows a photograph
made on a Wratten panchromatic. The panchromatic plates were
used in this work without the interposition of a colored screen
between the source and the plate. In practise, these plates are,
as a rule, used with a filter of such nature that the resultant
spectral sensibility of the plate is very nearly the same as the
visibility curve of the eye, thus giving correct rendering to the
different colors in the subject being photographed. Under such
conditions, with the filter adjusted to the plate and source, the
relative photographic efficiency, Er , of any source is approxi-
mately 100.
One plate typical of each class was chosen for use in this work ;
each is of medium speed and is a good average representative of
its group. Those used are :
a. Ordinary — Seed 23.
b. Orthochromatic — Special experimental plate.
c. Panchromatic — Wratten panchromatic.
SOURCES.
1. Sunlight. — A heliostat was placed outside a window at the
end of the photometer bench and a beam of sunlight reflected
inward along the axis of the photometer. The heliostat mirror
is of clear white optical glass, silvered on the back surface. The
illumination incident on the photographic plate was reduced to
0.1 meter candle by crown glass lenses. The exposures were
made between 1.30 and 2.30 p. m. on a clear day.
2. Skylight. — The heliostat mirror was set in such a position
that by looking down the photometric axis a portion of the sky
near the zenith could be seen. The window was then closed by a
diaphragm which allowed no light except that reflected from the
mirror to enter the room. Glass lenses were used to reduce the
intensity. Exposures were made between 2.30 and 3.00 p. m. on
a clear day.
JONES, HODGSON, HUSK: EFFICIENCIES OF ILLUMINANTS 971
3. Acetylene. — A standard acetylene burner of the type pre-
viously described was used. The flame is of the cylindrical type
and is screened down to give approximately 1.3 candlepower.
4. Screened Acetylene. — The above source was screened with a
blue filter of such quality that the transmitted light matches very
closely the color of average daylight.
5. Pentane. — A standard Harcourt pentane lamp was used, be-
ing adjusted in accord with standard specifications.
6. Mercury Arc. — A 200-250 volt quartz mercury arc running
at 220 volts and 3.4 amperes was used. A reflector consisting of
a highly polished plate of black glass 2 cm. thick was employed in
this case. All the light utilized was reflected from the first
surface (air-glass), such reflection being considered to be very
non-selective. The intensity was reduced by a pair of quartz
lenses.
7. Mercury Arc. — The above source was screened with a piece
of heavy lead glass 4 mm. thick, sold under the trade name of
"Nultra" and recommended for use in the absorption of the ultra-
violet rays. This glass is quite colorless and transparent, the
sample used having a transmission (measured visually) of about
90 per cent.
8. Mercury Arc. — The conditions were the same as described
under No. 6, the one exception being that a clear white crown
glass lens was substituted for one of the quartz lenses used prev-
iously.
9. Carbon Arc, Open. — An automatic feed arc, with carbons at
right angles, was used for this test. The positive carbon was
coincident with the photometric axis, the crater facing the sensi-
tometer. The arc was operated on 1 10 volts, d. c, and a current
of 6 amperes was used. The drop across the arc was about 60
volts. The positive carbon was about 6 mm. in diameter and was
cored. Intensity was reduced by glass lenses.
10. Carbon Arc, White Flame Carbons. — A 115 volt d. c. arc
with a 10 mm. white flame carbon below and a 13 mm. cored car-
bon above. The arc was connected so as to make the lower car-
bon -f and was mounted in such a way that the flame, which was
about 2.5 to 3 cm. long, occupied a position on the photometric
axis. The intensity was reduced by means of one quartz and one
9/2 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
crown glass lens. The voltage across the arc was about 85 volts
and the current 24 to 26 amperes.
11. Enclosed Arc. — In this case the arc was enclosed in a glass
cylinder provided with close fitting metal ends. The carbons were
of the ordinary cored type, placed at right angles to each other,
the positive crater being on the photometric axis and facing the
sensitometer. It was run on no volts, d. c, and consumed 8
amperes, the drop across the arc being 65 volts.
12. Aristo Arc. — This was an enclosed arc with carbons verti-
cal, positive above. It was operated on 220 volts, d. c, and con-
sumed 16 amperes. The length of arc was approximately 2.5 cm.
13. Magnetite Arc. — This was of the ordinary commercial type
running on no volts, d. c, and using a current of 4 amperes. In-
tensity was reduced by glass lenses.
14. Carbon Glow Lamp. — For these tests a 50-volt lamp with
hairpin type filament, giving 16 cp. at normal voltage was used.
Tests were made at several points, beginning at 1 cp. and running
up to 21 cp. The m. h. cp. was determined by the point to point
method and a reduction factor of 0.79 was assumed for obtaining
the mean spherical candlepower.
15. Vacuum Tungsten. — A 120 volt, 10 watt lamp or the or-
dinary commercial type was used. Reduction factor = 0.78.
16. Nitrogen-filled Tungsten. — A 120 volt, 400 watt lamp was
employed, tests being made at various points between 59 and 130
volts. Reduction factor = 0.86.
17. Photolite Tungsten, Blue Glass Bulb. — A 120 volt, 1,000
watt G. E. photolite was used, being operated at various voltages
from 55 up to 134. Reduction factor = 0.88.
18. A mercury-vapor arc in a glass tube 45 x 2.8 cm. was
used. The tube was operated on 115 volts d. c, the drop across
the tube being 33 volts with a current of 3.5 amperes. The
tube was mounted so as to intersect the photometric axis at an
angle of 900 and a diaphragm being so placed that a section of the
tube 2 cm. long midway between the ends of the tube and on the
photometric axis was used in exposing the plates.
EXPERIMENTAL DETAILS AND ERRORS.
In exposing the plates the source to be tested was placed on
the photometer and conditions so adjusted that the illumination
JONES, HODGSON, HUSE: EFFICIENCIES OF ILLUMINANTS 973
on the plane of the photographic plate was o.i meter-candle. For
sources under 14.4 cp. this was done by computing from the
known candlepower the distance required and setting the position
of the sensitometer accordingly. For sources of greater intensity
the reducing lenses were placed in position and the sensitometer
adjusted to such a position that the required illumination was ob-
tained. This was determined by readings taken on the illumin-
ometer attached to the sensitometer, the probable error of the value
thus determined being approximately ±2 per cent. A light tight
partition separated the source and photometric apparatus from
the portion of the room containing the sensitometer, an opening
on the photomertic axis admitting light from the source to the
photographic plate. Screening diaphragms placed at proper in-
tervals prevented any stray light from reaching the plate, while
being exposed. All walls and ceilings were painted dead black
to prevent reflections.
The photographic plates were backed in order to prevent hala-
tion and development was done with a standard pyro-soda devel-
oper used at a fixed temperature, 70 ° F. The plates were devel-
oped in a tray which was rocked continually by hand during de-
velopment. This method has been found to give the most satis-
factory results where uniformity of development is desired.
Three to six plates were exposed under each condition and the
average of the inertia values obtained was used in calculating the
photographic efficiency.
The experimental error liable to occur in work involving the
sensitometry of photographic materials are numerous and rather
large. By using a "falling plate" sensitometer all possibility of
errors due to an intermittent exposure was eliminated. Errors
arising from a failure of the reciprocity law were eliminated by
keeping constant the exposure time and the illumination on the
plate. The exposure times were determined to within ±0.2 per
cent, and the illumination on the plate to within ±2.0 per cent.
Variations due to lack of uniformity of coating and to inequalities
in sensitiveness may in some cases amount to as much as 20 per
cent, from plate to plate. However, by making several exposures
and averaging the results the uncertainty can be reduced to a
probable error of about ±5 per cent. The total probable error
974 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
in values given in this paper is estimated at approximately ±7
per cent.
RESULTS.
In Fig. 3 are shown three curves obtained from three groups
of plates (Seed 23) exposed to a nitrogen filled tungsten lamp
operated at three efficiencies. The exposure was the same in all
cases and the shift in the inertia value indicates the increase in
photographic efficiency corresponding to the increase in visual ef-
ficiency at which the lamp was operated. In Table I are given
the data obtained from the individual plates of the group from
which curve A, Fig. 3, was plotted. This table of data is pre-
sented merely to show the order of agreement that can be ex-
pected in work of this nature.
TABLE I.
Density
Step
Exposure
M. C. S.
No. 108
No. 109
No. no
No. in
Mean
I
0.06
O.O
O.O
O.O
O.O
O.O
2
0.08
O.OI
0.0
0.02
O.03
0.02
3
O.I2
O.05
O.03
0.09
O.08
O.08
4
O.17
O.16
O.I2
O.17
O.16
O.15
5
0.24
O.3O
O.27
O.27
0.26
O.27
6
0.34
O.46
0.43
O.42
O.41
0.43
7
O.47
O.68
0.63
O.63
O.58
0.61
8
O.67
O.92
0.87
0.86
O.83
0.87
9
0.94
I.20
1. 14
I. IO
I.09
1.13
10
i-33
1-43
I.32
1-43
I.29
i-37
11
1.88
i-73
I.60
I.60
i-57
1.62
12
2.66
1.97
I.83
I.87
1.82
1.87
13
3-75
2.29
2.13
2.IO
2.10
2.16
*4
5-31
2.72
2.38
2.45
2.48
2.51
15
7-5o
2.96
2.91
2.9I
3-i6
2.98
16
10.60
—
—
—
—
—
17
15.00
—
—
—
—
—
Log?
o.33
O.32
o-35
o.33
o-332
i
0.214
0.209
0.229
0.214
0.216
S
4.67
4-79
4-37
4.67
4.62
The results obtained from the exposures made to sunlight are
as follows :
On Seed 23 (ordinary blue sensitive)
log i = 2.86
i = 0.0725
Sensitiveness = —7- = 1^.8.
i
On Experimental Ortho. (orthochromatic)
log **= 2.71
i = 0.0513
Sensitiveness = — r = 19.5.
JONES, HODGSON, HUSE : EFFICIENCIES OF ILEUMINANTS 975
On Wratten panchromatic (panchromatic)
log i = 2.796
* = 0.0625
Sensitiveness =
16.0.
Fig. 5-
60
NITRO
SEN F
LLED
TUNG
>TEN
a-
b-
c-
ORDir
ORTI-
PANC
ARY P
OCHRC
HROM
LATE
MATIC
\T1C
0
u70
0
s*o
^0
e
''o
0
C
fceo
u
>
"6
c
'b
0
•"&
'5
iLl
0=50
S*
0 **
xt£
^
0 ^
*/-
LUME
«
WAT
r
10 12 14 16 15 20 22 24 23
Fig. 6.
Since sunlight is used as a standard of comparison in this work,
its efficiency on each plate is assumed to be ioo per cent, and the
relative photographic efficiency of any illuminant is obtained by
976 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
taking the ratio (xioo) of the sensitiveness value -r- obtained
with that source on a given plate, to that obtained with sunlight
on the same plate. This ratio is termed the relative photographic
efficiency and is designated by the symbol, Er . Therefore, if the
relative efficiency ~Er of a source is 50 per cent. , in order to obtain
a given effect on a photographic plate twice as great an exposure
(measured in meter candle seconds) must be given when using
that source as would be required in case sunlight were used.
In Table II is given a complete set of data obtained by using a
nitrogen filled tungsten lamp at various efficiencies on an ordi-
nary blue sensitive (Seed 23) plate. Four plates were exposed
at each efficiency and the individual log i values are given in the
table, the Er values being computed from the mean of each group.
The agreement between the log i values in this set is somewhat
better than the average with the exception of the third group. In
this group (at 9.67 lumens per watt) the maximum deviation
from the mean of the inertia values is -f-22 per cent. This is
much greater than the average deviation existing and can only
Fig. 7-
be ascribed to inequalities of coating or sensitiveness, since all
other errors are known to be less than ±5 per cent.
JONES, HODGSON, H USE I EFFICIENCIES OF ILLUMINANTS 977
59
78
TABLE II.
Source — Nitrogen-filled tungsten.
Watts, 400.
Volts, 120.
Reduction factor, 0.88.
Plate— Seed 23 (Ordinary, blue sensitive).
Exposure — Meter-candle seconds = 15.0.
Illumination on plate = 0.10 m.c.
Time = 150 sec.
Sensitometric data
Photometric data
Volts Amps. M.h.cp.
2.42
2.8l
30.8
Rumens
Watt
2.38
5.61
hog 1
o-33
0.32
o.35
o.33
M 0.33
0.26
0.26
0.26
0.27
M 0.26
0.214
-7- Er
4.67
0.182 5.50
34
40
95.6 3.12 274.0
8.55
0.29
0.15
0.20
0.18
0.20
0.160
6.25
45
3-34 5M.o
15.4
0.10
0.13
0.12
0.12
0.12
0.06
0.07
0.06
0.08
0.132
7.58
55
120 3.52 760.0
19.9
0.07
0.06
0.05
0.05
0.05
0.1 17
8-55
62
125 3.61 920.0
22.6
0.05
0.03
0.03
0.03
0.05
0.1 12 8.93 65
13° 3-66 1080.0
25.0
0.03
0.107
9-35
68
978 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
In Tables III to VI, inclusive, are given the summarized results
on glow lamps, as follows :
Table III — Carbon from 0.5 to 3.8 lumens/watt.
Table IV — Tungsten from 3.23 to 10.9 lumens/watt.
Table V — Nitrogen tungsten from 2.48 to 23.8 lumens/-
watt.
Table VI — Nitrogen filled blue bulb Photolite, 1.00 to 12.8
lumens/watt.
The data on these sources are given as curves in Figs. 4, 5, 6
and 7. The curves obtained are all straight lines within the
limits of experimental errors and over the ranges of efficiencies
used.
tXble in.
Source — Carbon glow lamp.
Volts, 45.
Watts, 40.
Reduction factor, 79.
Exposure — 15.0 meter-candle seconds.
Illumination == 0.10 m.c.
Time = 150 sec.
Photographic material
Visual eff.
lumen
watt
2-33
6.09
9.00
IO.9
Visual eff.
lumen
watt
Ordinary
Orthochromatic
Panchromatic
S
nr
S
Ur
S
Kr
0.51
1-7
12
4.2
22
5-1
32
I.09
2.2
17
4.8
25
5-6
35
I.79
2.6
19
5-9
30
6.2
39
2.25
2.8
21
5-9
30
6.6
4i
2.70
3-i
23
6.2
32
6.9
43
3-14
3-4
25
7.0
36
7-5
47
3-4i
3-7
27
7-4
38
7-5
47
3-9°
4.1
3°
7.2
37
7-7
48
TABLE IV.
Source — Tungsten glow lamp.
Watts, 10.
Volts, 120.
Reduction factor, 78.
Exposure — 15 meter-candle seconds.
Illumination = 0.10 m.c.
Time -- 150 sec.
Photographic material
S
3-1
4-3
4.8
5-2
Ordinary
23
31
35
38
Orthochromatic
S
6.05
7.2
8.4
8.9
31
37
43
46
JONES, HODGSON, HUSE: EFFICIENCIES OF ILLUMINANTS 979
TABLE V.
Source — Nitrogen-filled tungsten.
Watts, 400.
Volts, 120.
Reduction factor 88.
Exposure — 15 meter-candle seconds.
Illumination, = 0.10 m.c.
Time = 150 sec.
Photographic material
Visual eff .
lumens
Ordinary
Orthochromatic
Panchromatic
watt
S
Er
S
Er
S
Er
238.0
4.8
35
8.6
44
8-3
52
5.6l
5.o
40
8.8
45
9-1
57
8-55
6-3
46
IO. I
52
9-4
59
15-4
7-5
55
II.7
60
10.7
67
19.9
8.6
62
13.0
67
12.0
75
22.6
8.8
64
13-6
70
12.0
75
25.0
9.2
67
14.O
TABLE VI.
72
12.5
78
Source-
-Nitrogen-filled, blue
glass bult
1.
Watts, 1,000.
Volts, 120.
Reduction factor, 86.
Exposure— 15
meter-candle seconds.
Illumination =
= 0.10 m.c.
Time = 150 sec.
Photographic
material
Visual eff.
Ordi
nary
Orthochromatic
Panchromatic
watt
s
Er
S
B,
S
nr
0.9
6.8
49
8.4
43
9.0
56
3.22
8.7
63
IO.9
56
I0.6
66
5-8i
10.6
77
14. 1
72
12.8
80
8.48
12.4
90
l6.2
83
14.6
9i
10.6
15-3
in
19-5
100
16.6
104
12.8
16.3
118
20.5
105
18.1
113
The results obtained with other illuminants are summarized in
Table VII. The visual efficiencies of some were not measured
in this laboratory. In such cases the available data on the sub-
ject were consulted and from them an estimate of the efficiency
existing under the conditions of operation employed in this work
was made, such values being indicated by stars.
980 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
TABLE VII.
Photographic materials
Visual Ortho- Pan-
efficiency Ordinary chromatic chromatic
lumens , • , , « , , < ,
Source watt S Er S Er S ~Br
1. Sun *i5o.o 13.8 100 19.5 100 16.0 100
2. Sky — 25.0 181 30.0 155 2I.O 130
3. Acetylene *o.7 4.1 30 8.6 44 8.3 52
4. Acetylene screened *o.c>7 11. 2 81 16.5 85 14.2 89
5. Pentane *o.45 2.5 18 5.5 28 6.7 42
6. Mercury arc — quartz..-. *4o.o 83.0 600 98.0 500 59.0 367
7. Mercuryarc — nultraglass *35.o 30.0 218 38.0 195 26.4 165
8. Mercuryarc — crown glass *37.o 44.7 324 53.7 275 39.8 249
9. Carbon arc — ordinary. •• *i2.o 17.4 126 22.0 112 17.0 104
10. Carbon arc — white flame *29.o 35.5 257 46.5 234 34.4 215
11. Carbon arc — enclosed •• • *9.o 24.2 175 34.5 177 26.4 165
12. Carbon arc — "Aristo"... *i2.o 110.0 796 209.0 1,070 119.0 744
13. Magnetite arc *i8.o 14.6 106 22.4 115 13. 1 82
14. Carbon glow lamp 2.44 3.2 23 6.2 32 6.7 42
Carbon glow lamp 3.16 3.4 25 6.8 35 7.2 45
15. Tungsten evacuated 8.0 4.6 33 8.0 41 8.0 50
Tungsten evacuated 9.9 5.1 37 8.8 45 8.5 53
16. Tungsten nitrogen-filled 16.6 7.7 56 12. 1 62 11. 2 70
Tungsten nitrogen-filled 21.6 8.8 64 13.3 68 12.2 76
17. Tungsten blue bulb 8.9 13. 1 95 17.0 87 15.2 95
Tungsten blue bulb 11.0 15.0 108 19.3 99 17.0 106
18. Mercury-vapor *23.o 42.7 316 69.0 354 43.7 273
As previously stated the values of Er given in Table VII are
relative values and do not express the photographic efficiencies
of the various sources in terms of the energy consumption of
that source. As the efficiency in terms of energy consumption
is of considerable interest the values obtained have been reduced
to that basis and are given in Table VIII.
The inertia values (i) obtained from the characteristic plate
curves are expressed in exposure units, that is, meter-candle
seconds. The luminous flux incident upon unit area (1 square
cm.) at a meter distant from a source of 1 mean spherical candle-
power is -*—. ; = t, lumens. This is the value of the luminous
r 47rr 100
flux incident upon a unit area of a surface at which the illumina-
tion is 1.0 meter-candle. Then
i (in m. c. s.) . .
ie — 1 is the inertia value
100
- . lumens seconds
expressed in 5 .
cm.
JONES, HODGSON, HUSE : EFFICIENCIES OF ILLUMINANTS 981
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982 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Now, if the efficiency of the source used is E ( in ) the value
V watt /
, . . lumen seconds 1 . ,
remains the same when expressed in — . ■=- is the
watt second E
„ . . watt seconds ,
efficiency in : =-. and
lumen seconds
. _ i (in m. c. s. ) 1 _ watts seconds
1002 E cm.
. i (in m. c. s.) 107 _ ergs
100 E cm.
ie is, therefore, the inertia value expressed in ergs consumed at
the source per cm.* at the plate. This value is inversely pro-
portional to the photographic efficiency of the source when used
on that particular plate. The photographic efficiency may be
obtained, therefore, by taking the reciprocal of ie.
In order to make the results obtained on different plates com-
parable with each other it is necessary to use some source as a
standard. Sunlight is used as before, its efficiency being taken
as 100 on each plate.
The values of visual efficiency for many sources were not meas-
ured directly, but were estimated from the last available data
found in the literature on the subject. The values tabulated in
Table VIII are:
* (m. c. s. ) 103 _ ergs
E,=
E cm.1
1,000 ie (for sun)
(for particular source)
It will be noted by reference to the curves in Figs. 4, 5 and 6
that the curves of relative efficiency are straight lines slightly
convergent toward the higher efficiencies. The curve for the
orthochromatic material lies about midway between the other two
in each case. In the case of the gas-filled lamp with blue bulb
the curves for the ordinary and the panchromatic materials con-
verge and cross at Er = 95 per cent., while the ortho curve is
entirely below them. This is due to the fact that the glass of
which the bulb is made has an absorption band in the green, the
region of extreme sensitiveness for orthochromatic materials.
The light emitted is, therefore, relatively weak in the green and
JONES, HODGSON, HUSE '. EFFICIENCIES OE IEEUMINANTS 983
as a consequence gives low efficiencies on orthochromatic
materials.
The values of ~Er given in Table VII enable us to pick from
any group of sources the one giving the greatest photographic
efficiency when used in connection with either of the three typical
classes of photographic materials, for a fixed value of the illumi-
nation. The values in Table VIII, on the other hand, enable us
to choose for either class of materials, the source that is most
efficient photographically, from the standpoint of energy con-
sumption.
The choice of a source for any particular purpose frequently
depends on factors other than efficiency, but no attempt is made
in this paper to deal with such cases.
Other photographic materials such as wet plates, printing
papers and processes depending upon the sensitiveness of bichro-
mate involving different spectral sensibilities have not been dealt
with in this paper. The authors hope at some future time to
extend the measurements to cover such cases and also some other
illuminants not dealt with at this time.
The authors wish to acknowledge their indebtedness and to
express their thanks to Mr. R. B. Wilsey for his able assistance
rendered in connection with the experimental work involved in
this research.
DISCUSSION.
Mr. M. LuckiESH : I want to compliment the authors for this
excellent summary and also to point out the fact that there are
other important viewpoints from which to consider an illuminant
for photographic purposes. We, as lighting people, are inclined
to apply ordinary lighting criteria and ideals to the photographic
field, but it is easy to show this is not justifiable. I also want
to call attention to the fact that the so-called efficiencies of il-
luminants for photographic processes must be considered a good
deal as we should consider efficiencies in lighting; that is, the
element of satisfactoriness must enter which is determined by
many factors besides the photographic efficiency given here. This
discussion is not presented to detract from the value of this
excellent work but to emphasize the other viewpoints so that
10
984 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
the illuminating engineers will not overlook these facts and as-
sume that the illuminants from a practical standpoint lie in the
order given here because they do not. I am glad the authors
include Tables VII and VIII because in much of the photo-
graphic field, energy consumption (or photographic efficiency
given in Table VIII) is of minor importance provided it is
within reasonable bounds. Of more importance is Table VII
because it is necessary to have a light of high actinic value per
lumen in order to obtain portraits with short exposures and
without glare. In the portrait studios it takes only a few min-
utes to do the posing and make the exposure so it is seen that
other factors may easily over-shadow photographic efficiency
(actinic value per watt). Even in the moving picture studios
where excessive wattages are used, it has been found that energy
consumption is far from being the most important factor. Actinic
value per lumen, cost, portability, simplicity, color, etc., are
factors of great importance to those who use photographic il-
luminants especially in portraiture and moving picture produc-
tion.
I am pleased to note that the authors have checked my
measurements given for the gas-filled tungsten lamps. Through-
out my work in converting the gas-filled tungsten lamp (Trans.
I. E. S., Vol. X, No. 2, p. 149) into an acceptable unit for the
portrait photographers, the kind of plate used was of great
importance. The ordinary plate which is used very predomin-
antly in portraiture was the determining factor in the develop-
ment of this photographic tungsten lamp. Of course it is the
photochemists' dream that some day the panchromatic plate will
be in general use and that this plate will be cheap, efficient, and
capable of recording brightnesses in the same relative value as
the eye sees them. That may be the ideal but it is far from
realization, so that the ordinary plate must be recognized as the
determining factor in dealing with the practise of photography
in general. This was done in the development of the blue bulb
for the photographic tungsten lamp and therefore it is most
efficient for these plates. In Table VII, the light from this unit
is seen to be comparable with daylight in actinic value. Another
point of importance is the color of this light. It is a close match
to daylight when considered integrally. It does not match day-
EFFICIENCIES OF IEEUMINANTS 985
light spectrally, but this is of no importance for ordinary plates.
The fact that this light is approximately of the color and actinic
value of daylight has proved to be highly in its favor because
of the possibility of using it combined with daylight. Incidental-
ly, this illuminant is satisfactory for orthochromatic or panchro-
matic plates and for color-photography for orthochromatic or
panchromatic plates and for color-photography because all rays
are present in its spectrum although it is less efficient for these
processes.
I want to emphasize that it is necessary to distinguish be-
tween the photographic process and the visual process, as the
authors have done, and that in dealing with photography we
are dealing with a lot of 'eyes' that differ from each other a great
deal more than normal eyes differ from each other, and that
these photographic 'eyes' are in general tremendously different
in sensibility from the human eye. That means that we must
alter our criteria for judging illuminants for photographic pur-
poses. For instance, the life which may be considered the most
economical for an electric incandescent lamp for ordinary light-
ing service will not be the most economical for a photographic
unit. The authors have taken, no doubt, the incandescent lamps
operated at their normal efficiencies which are determined by
ordinary lighting service and the human eye. When we use
photographic units a few minutes now and a few in the next
hour, we can boost the efficiency up and the life down very
considerably, and approach a more economical operating point
for an incandescent lamp. As I have shown in my papers on
the subject, a slight increase in voltage causes a much greater
increase in the actinic value of the light from the tungsten lamp
for ordinary plates, with an accompanying reduction in life ;
however, by increasing the voltage, we have approached the most
economical point at which to operate these lamps for photogra-
phic purposes.
In order to avoid confusion I wish to distinguish between two
units, namely, actinic value per lumen and actinic value per watt.
The relation between these two units is fairly definite (if the
photographic process is specified) for a given illuminant but
the relation differs with each illuminant. Therefore, in general
there is no relation between the two units.
986 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Mr. h. A. Jones: In regard to Mr. Luckiesh's point con-
cerning other considerations coming in for photographic work,
I think the point is very well taken. As stated in the paper, we
do not attempt to cover all the points of advantage and disad-
vantage in the various sources; but only treat the subject from
the standpoint of illumination and energy; also, I might add,
there are a great many other photographic materials having dif-
ferent spectral-sensibilities which we have not treated here, such
as wet plates, bichromated gelatine, etc. In regard to the question
as to the Aristo arc and white flame — I believe that has been
answered very satisfactorily. The Aristo lamp was an enclosed
arc burning hard carbons and the white flame was an arc equipped
with the ordinary white flame photographic carbons burning open.
In regard to the quartz lamp, No. 6, the intensity in that case
was reduced by means of quartz lenses, as I believe is stated
in the paper. No. 7 was shielded by means of a piece of lead
glass designed and sold as an absorber of the ultra-violet, while
in the case of No. 8, thre same arc was used with the exception
that a piece of crown glass, such as is used in making photo-
graphic lenses, was substituted, in place of the lead glass. Of
course, the efficiency given in No. 6 could never be realized in
case a glass lens is used in the camera, while the efficiency of
No. 8 is the efficiency that would be realized in case a camera
with a crown glass lens were used. No. 18 is the Cooper-Hewitt
glass tube mercury-vapor arc. In regard to the term "falling
plate" as descriptive of the sensitometer used, I probably failed
to clearly define its meaning. The term is used among workers
in photographic sensitometry to differentiate between the class
of sensitometer in which the exposure is continuous, and those
in which the exposure is intermittent, as is the case when a
rotating sector is used. As a previous speaker has pointed out
it is not the photographic plate which moves, but a metal plate
in which apertures of varying lengths are cut. This plate travels
at a uniform rate between the photographic plate and the light
source.
GENERAL REPORT ON GLARE 987
GENERAL REPORT ON GLARE.*
Synopsis: The work of the committee the past year is summarized.
Tentative definitions are offered of different classes of glare and the
phenomenon of glare is analyzed and defined with as much precision as
seems possible at the present time. Limits of tolerance of the eye to
brightness conditions above which limits glare may be said to exist are
stated as definitely as possible. The twelve reports supplementary to this
general report of the committee are briefly outlined.
INTRODUCTION.
The word glare has been commonly used since the beginning
of illuminating engineering and its general meaning is fairly well
understood. However, both our definitions and our common
conceptions of what constitutes glare have not been definite or
well defined. The work of this committee the past year has,
therefore, been confined mainly to the analysis of glare into its
fundamental causes and the formulation of precise definitions
and data relating to glare. In addition to this general report on
the subject of glare the committee has prepared supplementary
reports which have been issued from time to time during the past
year as follows :
1. General report on glare (classification and definitions).
2. Diffusing media I (classes and definitions of diffusion).
3. Diffusing media II (measurement and theory of diffusion).
4. Papers and inks.
5. Photographic papers.
6. Window envelopes.
7. Interior furnishings.
8. Projection and focusing screens.
9. Diffusing glassware.
10. Effect of glare on vision.
11. Automobile headlights.
12. Interior illumination.
13. Street illumination.
Reports i to 9 were drawn up by the chairman of the com-
mittee, No. 10 by Richtmyer, No. 11 by the chairman, No. 12
by Cravath, and No. 13 by Vaughn.
* Report No. I. of the I. E. S. Committee on Glare.
988 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
CLASSIFICATION.
Conditions for Comfortable Vision. — The brightness of white
diffusing paper in the open on a clear day at noon is about three
candles per square centimeter or ten lamberts in full sun and
skylight, or about three lamberts if illuminated by sky alone.
This is about the upper limit of comfortable, accommodated
vision. The lower limit is about a millionth part of this or
3 x io-6 lambert, about the brightness of white paper illuminated
by full moonlight. The absolute limit of vision (white threshold)
is about 6 x io~10 lambert.
Now, the illumination of full sunlight would be an intolerable
glare under either of two conditions : (a) sudden exposure of an
eye accommodated to a much lower mean brightness or (b) a
steady exposure with surroundings very much less bright. The
first case is simply a lack of accommodation due to lack of time
for adjustment, the second is a similar lack of accommodation
due to the impossibility of accommodating to a bright spot and a
dark field at the same time. These illustrations indicate the
relation of glare to vision. Physiologically, glare, in its broader
interpretation, is the direct cause of strained brightness accom-
modation. There are four classes of strained brightness accom-
modation :
1. Brightness above the maximum limit of full accommodation.
Full noon sun on snow, sand or water are examples of excessive
brightness glare. Whatever the nature of the adaptation of the
retina to the brightness of the image upon it (rate of catabolism
of visual purple?) there is an upper limit to it. Brighter images
cause distress and excessively bright images, long continued, re-
sult in a temporary loss of dark adaptation (snow blindness)
lasting for from a few hours to a week. The sole remedy for con-
ditions causing brightness glare is the wearing of absorbing
glasses, those transmitting 1/10 of the light (/. e., of density
unity) are sufficiently absorbing for snow fields. The solar disk
may be viewed comfortably through a screen whose transmission
is one millionth.
2. Brightness greatly in excess of that to which the eye is tem-
porarily accommodated produces painful glare lasting nearly until
the retinal accommodation has reached the new level. Coming
GENERAL REPORT ON GLARE 989
out of a dark room into full daylight is a familiar example of
temporary glare. A single short exposure, such as is caused by
lightning at night, cause flash glare. A succession of flashes
constitutes flicker. All kinds of glare of this class may be attri-
buted to the lag of accommodation behind exposure. This lag
is a real visual economy, since we are constantly viewing objects
of different brightness and if there were no lag (amounting to
from half a second to several minutes) the wear and tear on the
accommodation would necessarily be considerably increased.
3. Brightness localized in a field of much lower or much higher
luminosity. This is the case of contrast glare or spot glare. The
retina tends to accommodate itself to that part of the image fall-
ing upon the fovea, in other words upon that part of the field of
view upon which the attention is centered. We have no data
at present on the distribution of the accommodation over the
retina in the case of excessive contrast within the field of vision
nor on how this varies with the (a) average luminosity of the
field (b) the size of the brighter areas or (c) the location of the
brighter areas with respect to the center of attention.
Details are discerned by means of differences in brightness and
color. Vision is at its best when contrasts are about 1 : 20, while
it is accomplished with effort at contrasts as low as 98 : 100 pro-
vided the general illumination be sufficient, and without sensible
discomfort if contrasts be less than 1 : 100. Contrasts as high
as 1 : 10,000 are not rare, in window frames against open sky,
illuminants against their backgrounds or in spots of specular re-
flection or transmission ; these constitute contrast glare.
The physiological basis of contrast glare, is, no doubt, some
sort of conflicting tendency among the sets of nerves controlling
retinal adaptation. The means of control of the different parts of
the retina are only partly independent, hence the general level of
adaptation represents a compromise between local tendencies in
different parts of the retina. With but moderate contrasts in
the field, there is no effort toward local adaptation. It is only
excessive contrasts which tend to cause the differential accommo-
dation resulting in discomfort.
In general, no protective glasses can afford any relief from
contrast glare. The sole remedy is to reduce the contrasts caus-
990 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
ing it by keeping excessively bright spots out of the field of view
or by properly using diffusing media of suitable quality. It is
only in cases of contrasting fields differing in hue that protective
glasses are of any avail. These should be of the dominant hue
of the darker part of the field.
4. Brightness below the minimum limit of accommodation
causes a strain of whatever controls the accommodation, provided
the object viewed be given concentrated attention. Reading
dimly illuminated matter is a familiam example. This is not glare
proper but a cause producing a related effect.
Our special report on the Effect of Glare on Vision (Report
No. 10) deals at considerable length with the various effects out-
lined above and includes the quantitative data at present available.
Some cases of glare intermediate between classes 1 and 4 re-
quire special consideration, cases in which a bright field is com-
posed of numerous fine bright points, granular glare for short.
Familiar illustrations are sunlight on rough water, frosted glass,
sand or rain drops, a starry sky and the like. The resolving
power of the eye is about half a minute of arc, that is, the image
of any object however small will have a diameter of at least 0.002
mm. on the retina. The image of a distant arc lamp, star or
glare spot is spread over this minimum diameter on the retina,
hence will appear of lower intrinsic brilliancy and contrast than
it really is. In certain cases this effect of angular size of detail
is of considerable importance.
Another class of glare producing retinal strain is that in which
the object of attention is overlaid with a veil either darker or
lighter than the object in which details are to be discerned. Pro-
jection on a screen in a lighted room, reflection from varnished
wood or glossy paper, a landscape viewed through a haze or a
dirty window upon which the sun is shining are illustrations of a
bright veil ; a landscape viewed through a wire screen not illumin-
ated is an example of a dark veil.
Such cases are called veiling glare. Only specular reflection
from a glossy surface causes actual brightness glare of the nature
of veiling but all cases of veiling cause interference with vision.
The resulting discomfort depends in large measure upon the de-
gree of attention given the object viewed.
GENERAL REPORT ON GLARE 991
The pupillary diameter varies from 2 mm. to 7 or 8 mm. ; that
is, the area of the pupil varies in the ratio of about i to 15 in
extreme range. The extreme range of retinal sensibility is of the
order of ten million to one, so that in the total brightness accom-
modation of the eye, pupillary expansion and contraction play
but a minor part. It is very desirable to know the size of pupil
and retinal sensibility corresponding to each brightness of field
of vision and a sub-committee is at present engaged in obtaining
this data. The only data at present available is that of Nagel
(see Helmholtz, phys. Optik, II, 264) and others on the increase
of dark adaptation with time. Five observers obtain data in
substantial agreement. Starting with ordinary daylight interior
accommodation, the minimum perceptible brightness corresponds
to the flux density given by one meter candle. The reciprocal of
this minimum increases with time in the dark about as follows :
Minutes adaptation 0.5 4 9 04 19 31 61 (960)
Threshold sensibility ... 20 75 1,850 10,400 26,000 174,000 215,000 270,000
This may be represented by the equation
log I/I0 = 6.43 (1 — e-°™*)
t being the time of dark adaptation.
The effect of glare on vision is the basis upon which it is classi-
fied and defined. The fact must be strongly emphasized that it
depends not upon the objective brightness of the field viewed but
upon the subjective brightness sensation. The eye observes
brightness and variation in brightness but the scale reading (sen-
sation) is not proportional to the stimulus (light flux) over the
whole range of the instrument. It is impossible to measure di-
rectly the brightness sensation corresponding to each brightness
observed but relative values may be determined by an indirect
method.
The sensibility of an instrument is the derivative of its scale
reading with respect to the stimulus. Now, the photometric sen-
sibility curve of the average normal eye may be (Nutting, "Ap-
plied Optics," p. 127) well represented by the function P = Pw -|-
(1 — Ptw) (B/B0)«, B being the (meter-candle) brightness and
B0 the threshold value, and Vm the minimum perceptible photom-
etric difference, about 0.017. The general integral of this or
S = C log [1 + (1 — P»*)(B/B0)» — *]x/"
992 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
gives the general relation between brightness sensation S and
objective brightness B. Over a wide range of moderate bright-
nesses this reduces to Fechner's law, S = K log (B/B0). These
relations must be used in dealing with contrast when the field of
lower brightness is below that corresponding to a meter-candle
on a white reflecting surface.
DEFINITIONS.
Glare. — Glare is brightness within the field of view of such a
character as to cause discomfort, annoyance or interference with
vision. As pointed out above, glare causes other subjective visual
effects and impaired vision may be due to causes other than
glare. However, it does not appear feasible to broaden the defi-
nition without making it include all forms of improper or defec-
tive illumination.
Brightness Glare. — Brightness glare is glare due to an excessive
general brightness of the field of view. A brightness approaching
or exceeding that of white paper in direct sunlight is considered
excessive. The upper limit of comfort for fully accommodated
eyes is about 3 lamberts or 1 candle per square centimeter. This
limit is illy defined but of nearly the same value for all normal
eyes so far as known. If any quantitative expression is to be
chosen for brightness glare probably the most rational would be
G* = log (B/B0)
in which B is the brightness causing the glare to be specified and
B0 is the upper limit of comfort. Thus, a brightness glare of
1 corresponds to a brightness of 30 lamberts, a glare of 2 to 300
lamberts, and so on.
Contrast Glare. — Contrast glare is glare due to excessive con-
trasts within the field of view. A proper measure of contrast
glare is relative total brightness. This holds for the moderate
working brightnesses. Relative total brightness is, for nearly
normal illumination,
_B_ _ Brf-f B5 <*Rd + irRs
B' ~~ B'd -f- B, toR'd + irR's
in terms of specular and diffuse brightness Bs and B<* , specular
and diffused reflecting power R5 and Rd and solid angle w sub-
tended bv the source.
GENERAL REPORT ON GLARE 993
A quantitative expression for contrast glare applicable at all
brightnesses from the threshold of vision up to the highest that
are utilized is an expression for the difference in the brightness
sensations
n -Ifw i +Pm(B1»/B0«-i) _ \
^c ~ n \ g i + Pm (B2"/B0« — i) /
Pm being the least perceptible photometric difference (about
0.017), Bx and B2 the brightnesses (objective) of the contrasting
areas, B0 the threshold brightness and n a constant equal to about
0.35. The constant 2 signifies that glare begins at contrasts
of 100 : 1. This expression is to be used with care since contrast
glare varies to some extent with the length of the boundary
along which contrast occurs, with the part of the retina upon
which the brightest part of the image falls, the degree of general
accommodation and other factors.
Veiling Glare.— Veiling glare is that cause of impaired vision
due to a light or dark veil obscuring the field of view and of a
pattern different from that of the object viewed. The veiling
due to a bright veil is greater, the greater the (sensation) bright-
ness of the veil relative to that of the field to be viewed. If the
veil is a network or a uniformly illuminated area, probably a
mean brightness would serve as a measure of veiling. A quanti-
tative expression for bright veiling glare that would serve is a
statement of its effect in reducing contrast. Suppose a veil of
brightness V overlies a contrast measured by B/B1. Then
1 B 1 B + V
Gv = log ^ log B, y
For example, if on a glossy printed page, the contrast between
paper and ink is 20 : 1 away from the specular angle and 1 : 1 at
the specular angle, then the veiling glare in the latter case is log
20 or 1.3.
Dark veiling is difficult to describe in terms of brightness. It
involves a sacrifice of both brightness and definition. The latter
effect is so considerable in proportion to the first that a quanti-
tative definition based on brightness alone is of little service.
Temporary Glare and Flicker.— Temporary glare is glare caused
by temporary lack of brightness accommodation of the retina.
Temporary glare is greater the greater the brightness of the newly
994 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
exposed field relative to that of the field to which the retina is
accommodated. Now, the only known means of estimating the
level of brightness accommodation (see below) is by the magni-
tude of the threshold. If, now, glare is to be estimated by the
ratio of the new brightness to which the eye is tending to accom-
modate itself to the brightness to which it is already accommo-
dated the temporary glare is properly measured by
G< = kg -|s- — 2
where Bx and B2 are the two thresholds in question and the con-
stant signifies that glare begins at a ratio of brightnesses of
100:1. This expression is similar to that for contrast glare
(see above) but simplified.
Flicker involves not only the ratio of two brightnesses but the
rate of accommodation. The brightness sensation, at ordinary
brightnesses, rises to half its value in about 1/20 second, flicker
appears most pronounced at 8 or 10 cycles per second, that is
with the transition from dark to light occupying about 1/20 second.
At low mean brightnesses the rate of accommodation is very much
slower. Fluctuations in brightness as slow as i per second are
very disagreeable. Experiment shows that flicker disappears at
a frequency proportional to the logarithm of the brightness. No
simple expression more than approximately expresses the relation
of flicker sensation to frequency and brightness.
GLARE IN PRACTISE.
Since the photometric sensibility of the retina and, therefore,
the sensation of brightness, varies enormously with the brightness
of the field of view, any criterion for glare is incomplete unless
the temporary retinal sensibility be specified. The fact that this
sensibility varies continuously increases the difficulty of specify-
ing it.
The only practical way out of the difficulty appears to be to (i)
specify sensibility in terms of the mean level of brightness to
which the eye is accommodated and (2) choose and name a
limited number of those levels of brightness corresponding to
practical working conditions. We, therefore, consider practical
lighting problems in glare from the standpoint of the four fol-
lowing different levels of accommodation :
GENERAL REPORT ON GLARE 995
i. Bright daylight in the open. The brightness of the field of
view, excluding such extremes as deep shadows and specular
reflections of the sun, ranges from nearly white objects in the
sun (2 to 10 lamberts) and the open sky (1 lambert) down to
foliage (y2 lambert) and moderate shade (V10 lambert). Prob-
ably 1 lambert is a fair average for the brightness to which the
eye is accommodated under this condition of illumination.
2. Interiors in full daylight. Again excluding such excessively
bright objects as those in direct sunlight and such dark objects
as deep shadows, the brightness of the field of view in interiors
on a bright day varies from the sky at 1 lambert, white paper
(0.1 to 0.04 lambert) and walls with a brightness of about 10
millilamberts, down to rugs, dark objects and moderate shadows
1 to 10 millilamberts in brightness. In this case 10 millilamberts
is a fair average level of brightness.
3. Interiors artificially illuminated. Unshielded illuminants
range in brightness about as follows : arcs from 10,000 to 200,000
lamberts, gas-filled tungsten lamp filaments 5,000 to 8,000 lam-
berts, ordinary tungsten 200 to 500 lamberts, carbon filaments
150 to 300 lamberts, gas mantles 50 to 200 lamberts, acetylene
flames 50 to 200 lamberts, gas flames 5 to 40 lamberts, kerosene
oil flames 5 to 100 lamberts. Frosted lamp bulbs range from
1 to 50 lamberts in brightness while diffusing globes and bowls
vary from 0.1 to 1 lambert. Such illuminants are supposed to
be outside the range of vision except at rare intervals. Objects
within the field of view vary from 10 millilamberts down to 0.01
millilambert and lower. A brightness of 0.1 millilambert is about
an average for the field of vision in interiors at night. If the
illuminants are not properly placed so that one or more of them
is continuously or frequently within the field of view, of course
the mean eye adaptation is such as corresponds to a higher mean
brightness than 0.1 millilamberts.
4. Night Street Illumination. The range of brightness within
the field of view out of doors at night is enormous. Excluding
artificial light sources viewed directly (see preceding paragraph)
the various brightnesses ordinarily within the field of view are
roughly: white objects in full moonlight 0.01 millilambert, foli-
age, roads and pavements in full moonlight 0.0005 millilambert.
996 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
The same objects under starlight are about 1/20 as bright. Objects
can be just descerned with full accommodation at about io-6
millilamberts. Considering only brightnesses necessary and com-
fortable to the eye, probably 0.00 1 millilamberts represents a
fair average for night vision in the open.
The four levels of brightness determining the four chief levels
of accommodation may be thus summarized.
Average Preceptible Relative
brightness percentage retinal
level difference sensibility
i. Exterior daylight 1000 ml. 0.0176 1
2. Interiors in daylight 10 0.030 59
3. Interiors at night o. 1 0.123 1430
4. Exterior at night 0.001 0.79 22300
The percentage perceptible difference is the difference in bright-
ness that is just perceptible (from data of A. Konig) expressed as
a fraction of the whole. Retinal sensibility in the last column is
proportional to the increment just perceptible calculated from the
data of Konig. Such data are to be regarded as tentative only.
Your committee is now engaged in its direct determination.
Such data give a basis for the quantitative estimation of glare
under various conditions. For example, assuming the above data
correct, an area so bright as to be blinding in broad daylight must
be about 60 times as bright as one that is blinding in an interior
in the daytime and 22,000 times as bright as a surface blinding
at night out of doors. The light sufficient to read by, to just
distinquish objects by and the brightnesses causing fatigue or
strain are known to vary in somewhat similar proportions at
the different levels, but exact data are not yet available.
At each level of accommodation a number of brightness sensa-
tions may be denned (such as dazzling, blinding, excessive, un-
comfortable, annoying, normal, defective, deficient, signal and
threshold) in terms of the brightness causing them relative to the
mean level. It may be desirable ultimately to define quantita-
tively a set of such terms but only after the relation of each to
brightness and angular area shall have been investigated.
An important relation that has been noted by several writers
should be emphasized here, namely that the more contrasty the
field of view the higher the level of illumination demanded by the
eye for acute, comfortable vision. In machine shops where large
GENERAL REPORT ON GLARE 997
dark areas are general and specular glare common, much more
light is required for good seeing than in say a living room with
no specular surface, indirect lighting and light walls and floors.
Your committee are not prepared to state the relation between
proper average brightness and mean contrast but do not doubt
that such a relation exists and that it may be determined and
formulated. Data are now being obtained by a sub-committee.
The special reports prepared by this committee are listed below.
Report No. 6 was prepared at the request of the National Letter
Carriers Association, No. n at the request of the Automobile
Association. The remaining reports were prepared solely in the
interests of illuminating engineering:
REPORTS OF COMMITTEE ON GLARE.
1. General Report on Glare. — Nature of various classes of glare,
the effect of each on vision, limits of tolerance and means
of suppression.
2. Diffusing Media I. — Classes of diffusion, nomenclature and
physical theory of diffusion.
3. Diffusing Media II. — Instruments and methods for measuring
diffusion and theory of diffusion photometry.
4. Papers. — Print papers, sizings, fillers, inks. Writing papers
and inks. Typewriting papers, inks and carbons. Draw-
ing papers and India inks. Tracing papers and cloths.
Blue print papers. Photostat papers.
5. Photographic Papers and Plates. — Glossy, semi-glossy, semi-
mat, velvet, rough and mat papers. Stocks, finished
papers and developed papers in three densities. Raw
plates, negatives.
6. Windozv Envelopes. — Diffusion analyses of various kinds in
use.
7. Furnishings. — Walls, ceilings, floors, woodwork, fixtures,
shades, draperies and furniture; unfinished, finished, and
covered. Brightness, contrast and veiling glare.
8. Projection and Focusing Screens. — Washes, cloths, metal
and special coverings. Focusing and translucent projection
screens.
9. Diffusing Glassware. — Ground, frosted, etched and flashed
globes and shades.
998 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
10. Effects of Glare on Vision. — Excessive and deficient illumin-
ation, temporary glare, excessive contrast, veiling, fatigue,
annoyance, discomfort, loss of brightness adaptation, loss
of acuity, permanent injury.
11. Automobile Headlights. — Causes of excessive glare, mini-
mum requirements in lighting and warning. Headlight
regulation.
12. Interior Illuminants. — Intensity, character and position of
lighting units.
13. Street Lighting. — Character, brightness and spacing of light-
ing units.
The character of each report is indicated by the brief outline
of each. Reports 2-9 inclusive deal with diffusing media, No. 10
with visual effects and 11, 12 and 13 with practical engineering
problems. In Report No. 2 are defined various terms used in
dealing with scattered light such as reflecting power, transmis-
sion, opacity, turbidity, entrant scatter, exit scatter, optical density
and specific density, contrast and gloss. In the report on papers
are given the results of complete diffusion analyses of many kinds
of papers, inks, fillers, sizing, etc. Of particular interest are
gloss, specific density, back reflection and contrast ratio. Photo-
graphic papers are produced with a wide variety of accurately
reproducible surfaces such as rough, textile, mat, semi-mat, semi-
glossy and glossy, each having, in the finished print, a wide range
of diffuse reflecting powers. It is on account of the interest
attached to the study of such surfaces that this report is included
in the series.
Window envelopes are desired as transparent and as free from
diffusion as possible, properties quite the opposite of those re-
quired of print papers. The ease with which print may be read
through the prepared window is quantitatively defined in con-
trast ratio. The specular and diffuse reflecting power of in-
terior furnishings, upon which home and office comfort so largely
depend are discussed in report No. 7. In the report on projection
screens (No. 8) are given accurate diffusion analyses of various
types of screens. Screen efficiency is defined and the properties
of an ideal screen and of the best realizable screen given. Diffus-
ing glassware is treated from both the laboratory and engineering
GENERAL REPORT ON GLARE 999
points of view. Report No. 10, on the effects of glare on vision,
is one of the most important of the series since its effect on the
eye is the ultimate criterion not only of glare but of good and
bad lighting. Report No. 12 deals with various engineering
problems in interior illumination and No. 13 deals in a similar
manner with street illumination.
A complete bibliography of glare and related effects would be
very extended ; nearly all the literature of glare is readily avail-
able in the Transactions of our society. To those desiring to
read further on the subject we recommend the various reports of
the committees on glare, the papers by Dr. Cobb on the effect of
glare on visual acuity, of Professor Ferree on the effect of ex-
cessive and deficient illumination, Mr. Luckiesh on glare in its
various aspects, Mr. Cravath on brightness, Mr. Minick on head-
lights and Mr. Sweet on street illumination.
Your present committee has felt that the work most urgent for
them to do lay in the field between the optical laboratory and
illuminating engineering and extending into both. We have en-
deavored to secure the data and formulate the relations most
needed by the illuminating engineering profession in improving
illumination and lighting practise, leaving to later committees the
work of expanding and popularizing this material.
Your committee consider that the line of progress in glare re-
search lies in the further investigation of adaptation levels of the
retina, of local and partial adaptation and of limits of tolerance
in proper lighting. Another line of work urgently demanding
attention is required to fill the gap between laboratory and prac-
tical engineering data.
Nelson M. Black,
J. R. Cravath,
F. H. Gilpin,
M. Luckiesh,
R. K. Richtmyer,
F. A. Vaughn,
P. G. Nutting, Chairman.
:i
IOOO TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
THE EFFECT OF GLARE ON VISION.*
Synopsis: What is known of the visual effect of radiation is out-
lined. Retinal phenomena, retinal adaptation to flux density, optic images,
pupillary adaptation and deleterious effects of radiation are discussed.
The following subjects are also discussed briefly: glare and vision; effects
of excessive brightness, momentary and continuous; conjunctivitis; kera-
titis; retinitis; effects of excessive contrast; discomfort, interference with
vision; effects of excessive extra visual radiation; and effects of veiling
glare and flicker.
INTRODUCTION.
In many respects the viewpoint from which this report of the
effect of glare on vision is written must necessarily differ ma-
terially from that of other reports in this series. Many, if not
all of these reports deal to a greater or less extent with definite
quantitative data, on the basis of which precise statements of
facts are possible. With visual phenomena, however, particularly
in connection with the deleterious effects of glare, little data,
qualitative or quantitative, is to be found, and what there is seems
more or less conflicting. To a large extent, therefore, this re-
port is to be regarded as the committee's opinion as to the nature
of the effects of glare on vision, as based on evidence now avail-
able. On account of the necessity for brevity, detailed refer-
ences have been omitted.
Since any discussion of the physiology of glare must be very
closely connected with the more general question of the deleterious
effects of radiation on vision, a few introductory statements seem
necessary regarding radiant energy, the eye, and the physiology
of vision.
The general nature of the propagation of energy by wave
motion is assumed to need no discussion here. Excluding X-ray
radiation the shortest waves yet observed have a wave-length of
0.000006 cm. From this point, the known wave-length extend in
an unbroken sequence up to the longest electromagnetic waves,
the length of which is measured in miles. This series is fre-
quently thought of as divided into four parts : ( 1 ) the ultra-
violet, extending from the shortest known waves (excluding
* Report No. 10., I. E. S., Committee on Glare, 1914-15.
THE EFFECT OF GLARE ON VISION IOOI
X-rays) up to the point where ordinary vision begins, somewhere
in the neighborhood of 0.00004 cm.; (2) the visible, extending
for one octave from about 0.00004 cm. up to the upper limit of
vision, approximately 0.00008 cm.; (3) the infra-red, extending
from here up to waves a few tenths of a millimeter; (4) beyond
this point begins the region usually thought of as comprising the
electromagnetic waves.
Similarly, the known effects of radiation can be divided into
four classes. (1) The heat effect; (2) the chemical effect; (3)
electric and electromagnetic effects ; (4) the visual effect.
The division of the spectrum into four parts is obviously quite
artificial. It is based solely on the circumstance that the visual
effect comprises the octave between 0.00004 and 0.00008 cm.
The same may be said regarding the classification of the effects
of radiation. It might be safe to predict that when our knowl-
edge of physical processes is sufficiently extended we shall explain
all phenomena on the basis of the electromagnetic effect.
The heat effect of radiation throughout the spectrum is pro-
portional to the energy at each wave-length. Since in the spectra
of modern illuminants the energy is greatest in the infra-red,
the infra-red waves have sometimes been called heat waves. This
classification is evidently erroneous. In this sense all zvaves are
heat waves.
The chemical effect of any part of the spectrum is a function
of both the energy contained in, and the wave-length of, that part.
In other words, the chemical effect is selective. No definite
statement of its extent can be made. In general the shorter
visible rays and the longer ultra-violet rays are the more active
chemically. But it is quite incorrect to speak of violet and ultra-
violet radiation as chemical radiation. Photochemical effects are
known well into the infra-red.
Regarding the electromagnetic effect, little need be said in this
connection. Since radiant energy is itself electromagnetic, its
effects must be ultimately expressed in those terms.
THE VISUAL EFFECT OF RADIATION.
As to the ultimate nature of the visual effect, with which we are
directly concerned in this report, it would obviously be evading
the question to say that it is electromagnetic. For while such
1002 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
a statement is probably true, broadly speaking, we cannot explain
the transformation of radiant energy into visual sensation by
means of what are now recognized as electromagnetic phenomena.
There are no reasons for assuming that the visual effect of
radiation is simply a heat effect. The latter, as explained above,
is common to all parts of the spectrum, while the former is
highly selective. Further, granted that there might be in the
retina a selectively absorbing medium capable of making possible,
by temperature changes, the selective character of vision, it is
difficult to conceive of the myriad of visual sensations being pro-
duced by thermal phenomena. It is, of course, true that a visual
sensation results from electric currents in the optic nerve fibers,
and it is further known that light, falling on the retina, produces
electric effects in the optic nerve. It is thinkable that the rods and
cones of the retina are sensitive thermo-electric receivers. Our
knowledge of thermo-electric phenomena, however, does not point
to it as a suitable basis for a working theory of vision.
There remains, as a basis for an explanation of visual
processes, the chemical effect. About all that one is warranted
in saying at the present time is that an explanation on this basis
is a possibility. Several hypotheses have been advanced but all
are but little more than speculation.
Since so little is known of the fundamental processes by means
of which radiant energy is transformed into visual sensation, it
is evident that any discussion of the peculiarities of these processes
must be either empirical or superficial.
RETINAL PHENOMENA.
The reception of radiant energy on the retina is known to
produce at least three results in the retinal media :
(i) A change in shape of the cones. The tips of the cones
recede when illuminated, due to the body of the cone becoming
shorter and thicker. (2) Closely connected with (1) is the so-
called "migration" of the dark pigment. On exposure to light
the pigment bearing cells push up towards the tips of the rods
and cones. Conversely, they recede toward the base of the cones
in darkness. This pigment migration has been found in some
lower animals but has never been observed directly in mammals.
(3) Most significant of all, the visual purple, a watery fluid purp-
THE EFFECT OF GLARE ON VISION IOO3
lish in color, is bleached to yellow or even "white" on exposure
to light. Different wave-lengths have different bleaching powers.
A curve showing the bleaching power of various parts of the
spectrum is quite similar in shape and position to the luminosity
curve. The chemical or physical changes corresponding to the
bleaching of the visual purple are not known. Nor is anything
definitely known regarding the relation of this phenomena to
visual sensation. Several hypotheses have been advanced but
all have obvious difficulties.
Among the retinal phenomena which may be observed subjec-
tively and which have an important bearing on the subject of
glare may be mentioned two :
(1) Retinal adaptation, frequently called light or dark adapta-
tion, is a phenomenon well known, qualitatively at least, to every-
one who has experienced the sensation of not being able to see
when first entering a darkened room from full daylight ; or, the
reverse, the pain experienced when first going from a darkened
room into full sunlight. Quantitatively, retinal sensibility is
defined as the reciprocal of the minimum observable (threshold)
illumination. In terms of the meter-candle on a white surface.
the retinal sensibility is nearly unity for the eye adapted to sun-
light. On entering a dark room, adaptation is rapid at first,
then slower and slower. It continues until at the end of an hour
it has reached a value of about 200,000. That is, after an hour's
rest in the dark the minimum observable illumination is 1/200,000
of what it is with the eyes accommodated to sunlight.
The return from a condition of dark adaptation to light adapta-
tion is much more rapid, being accomplished in a few seconds.
One important result of the phenomena of adaptation is that,
under different condition, the same sensation may be caused by
widely different brightnesses. Thus, with the eye adapted to sun-
light, the threshold sensation is just caused by 1 meter candle
on a white surface. But with the eye adapted for one hour,
the same sensation can be caused by 1/200,000 of a meter-candle.
One might conclude therefore, that with the sunlight adapted eye
an illumination of 100 meter-candles would cause the same sen-
sation as 1/2,000 of a meter-candle with the eye dark adapted.
This does not necessarily follow. For with the eye exposed to
1004 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
1/2,000 of a meter-candle, it is no longer in a condition of adap-
tation where 1/200,000 meter-candle excites the threshold sensa-
tion, on account of the rapid change from dark toward light
adaptation noted above.
Whatever may be the nature of the processes by which radiant
energy is transformed into visual sensation, or by which adapta-
tion may be accomplished, it seems reasonable to assume that
there is at least a rough correspondence between sensation and
the physiological activity which causes it. In other words, the
intensity of physiological reactions produced by the reception
of radiant energy on the retina depends both on the flux density
of that radiation at the retina and on the state of adaptation of
the eye.
(2) Brief mention should be made of the formation of after-
images in the eye. Two kinds of after-images are recognized.
(a) Positive After-images. — If the eyes be kept in the dark
for a few minutes, and then suddenly exposed for two or three
seconds, a "positive" image of the field viewed will be seen. This
will gradually fade. The intensity of the after-image caused
by a given brightness depends on the condition of adaptation
of the eye. With the eye fully dark adapted one may observe
the positive after-image of a window looking out on a moon-
lighted scene. With the light adapted eye far higher intensities,
those usually met in daylight, are necessary to produce after-
images.
(b) Negative After-images. — These may be observed by gaz-
ing steadily for two or three minutes at a field in which there is
excessive contrast. On looking at a white wall a "negative" after-
image is observed. With negative after-images thus observed,
not only are light and shade reversed, but colors are usually seen
complementary. Negative after-images frequently follow a
faded positive after-image.
The following two statements may be made, based on the phe-
nomena of after-images : ( 1 ) The physiological processes set
going by the reception of radiation on the retina persist for some
time after the radiation is cut off. (Positive after image.) (2)
The ability of any part of the retina to respond to a given stim-
ulus depended on its immediate previous history ; thus, where one
THE EFFECT OF GEARE ON VISION IOO5
observes the negative after-image on the white walls those parts
of the retina previously stimulated in excess of their surroundings
are not able to produce from the same stimulus as great a sensa-
tion as their surrounding parts.
Pupillary adaptation, as a result of varying brightness, is well
known. Under normal conditions, the size of the pupil may vary
from something less than 2 millimeters to something over 7 milli-
meters, causing by "stopping down" the optical system of the
eye a variation in brightness of the physical image found on the
retina of from 1 to 20. Pupillary adaptation is a function of
the actual brightness of the field viewed, of the state of retinal
adaptation, and perhaps also of the color of the active light. It
is "a reflex act, secondary to retinal stimulation."
MEANS AVAILABLE FOR STUDYING EFFECTS
OF RADIATION.
The above are some of the ocular phenomena incidental to
vision. If one excludes such unusual cases as snow blindness,
ultra-violet "burns," etc., which are seldom if ever experienced
by the average individual, we know of no structural change in
eye media coincident with any of the deleterious effects of rad-
iation on vision. These disturbances produced are largely func-
tional, and they must, therefore, be studied by such phenomena,
observable objectively or subjectively, as are known to be closely
connected with the processes which result in visual sensation.
For example, a study of retinal adaptation gives much inform-
ation regarding the pathological condition of the retina. The
following clinical observations are illustrative :
Several patients (Arch. f. Ophth., vol. 82, p. 509) complained
of flickering sensation, inability to see clearly for a long time
after coming into a light room from a dark room, and other
general disturbances to vision, due, apparently, to working under
improper artificial illumination. A test of the time adaptation
curves showed threshold sensibilities far below normal, indicating
a serious functional disturbance — whatever its nature — in the
retina.
Likewise, observation by means of after-images, pupillary re-
actions, examination of the light and color limits of the periphery
1006 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
of the retina are some of the phenomena by which the oculist can
study functional disturbances in the eye.
GLARE AND VISION.
Below will be briefly summarized some of the effects of the
various recognized types of glare on vision. For purposes of
this report, we will keep in mind the effect of each of the several
types of glare as follows : (a) Effect on external and internal
eye media, (b) effect on muscular apparatus of the eye, (c) func-
tional disturbances produced in the retina. The last is by far the
most important.
EXCESSIVE BRIGHTNESS.
Glare due to excessive brightness may be of two kinds : ( i )
momentary, (2) continuous.
When the more or less completely dark adapted eye is suddenly
exposed to a higher illumination, the eye is "caught unawares"
with the pupil wide open and with the retina in a condition to
register weak light intensities. Excessive retinal stimulation re-
sults. This causes a "blinding sensation," as a result of which
there is a sudden contraction of the pupil so intense as to be
painful. There seems also to be some reason to believe that the
intense stimulation of the retina causes pain. Very quickly the
retina adapts itself to the new intensity — or at least attempts to
do so. If the brightness is not too intense, a condition of com-
parative comfort is soon reached. The glare is then said to have
been momentary. In probably the vast majority of cases there
has been no injury, even temporary, except when the process be
repeated rapidly, many times in succession, or when the eye is
exposed to an excessively brilliant momentary flash.
In some cases, however, the brightness may be so intense that
the sensation of discomfort or pain does not disappear after a
few seconds but persists. The glare is then said to be continuous.
Such conditions obtain when the eye is exposed to the excessive
brightness from large snow fields, deserts, the flash of an electric
switch, etc.
The reduction of the physiological activity by both pupillary
and retinal adaptation is not in case of continuous glare sufficient
to reduce the stimulus to an allowable maximum. There results
pain due in part to the continued attempt of the iris to close
THE EFFECT OF GEARE ON VISION IOO7
further ; excessive bleaching, without possibility of restoration of
the visual purple, and a general condition of muscular strain re-
sulting from squinting and tension of external eye muscles.
The effects appear to be much more harmful if the excessive
brightness is located beneath the general eye level. (This might
be anticipated by a consideration of the conditions under which
primitive man was developed.)
In cases of continuous glare due to excessive brightness of long
duration, there results such ocular disturbances as snow blind-
ness, desert blindness, etc., which, in addition to being accom-
panied by external irritating, result in a temporary or semi-per-
manent loss of power to dark adapt.
Among the classified disorders recognized by oculists as arising
from long continued exposures to excessive brightness may be
mentioned :
1. Conjunctivitis. — An inflammation of the conjunctiva, the
membrane covering the inner surface of the eyelids and the outer
surface of the eyeball. The eyes become blood-shot; there are
sensations of sandiness; sharp, shooting pains; heaviness of the
eyelids ; and marked dryness. Unless the exposure be of too long
duration, "recovery usually follows the removal of the cause."
2. Keratitis. — Inflammation of the cornea, accompanied by
cloudiness and consequent impairment of vision.
3. Retinitis. — Inflammation of the retina, with accompanying
functional disturbances.
Sun blindness (solar retinitis) has resulted in a number of
cases from direct observation of the sun. There is partial (or
absolute?) blindness of the central portion of the retina, defective
color vision, reduction of visual acuity, and an apparent distor-
tion of objects in the field of view. Frequently, ophthalmoscopic
examination of the retina shows no change, or there may be a
small orange spot near the fovea, with alterations in pigmenta-
tion. It is stated that in no case in which vision was reduced to
less than one third has there been full recovery of visual acuity.
Snow blindness may be so serious as to result in permanent
blindness. There are the ordinary symptoms of conjunctival and
corneal inflammation, spasmodic contraction of the eyelids, fre-
quently corneal ulcers, intense deep-seated pain when the eye is
1008 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
exposed to light (photophobia) quivering and unsteadiness of
vision, but no retinal changes observable by means of the ophthal-
moscope.
Until we know more about the phenomena of vision we can
only speculate on the ultimate nature of the retinal disturbances
incidental to the above diseases. For example, continuous ex-
cessive brightness causes an excessive bleaching of the visual
purple. Now if this acts in an electro-chemical way to produce
vision, the physiological processes caused by it are continuously
over-stimulated, as are likewise the processes by which the visual
purple is renewed. Obviously, as in any bodily function, what-
ever the nature of the processes underlying vision, the excessive
stimulation of any or all of them for a long period must result in
a lowering of the efficiency with which they can be carried on.
In other words, the deleterious effects of excessive brightness
seem to be primarily due to continued over-stimulation of the
retinal processes by visible radiation rather than to the presence
of extra-visual radiation.
The obvious remedy for glare due to excessive brightness is
the use of neutral tinted glasses of suitable density.
EXCESSIVE CONTRAST.
Glare due to excessive contrasts occurs when the general level
of the brightness of the visual field is not above the upper limit
for which the eye can readily adapt, while within the field there
exists more or less restricted areas whose brightness is much
above this level.
The brightness of these areas may be (i) so great as to cause
of themselves, injury by over-stimulation of restricted areas (as
in the case of bare light sources) or (2) they may be such as to
cause simply a reduction of visual acuity and the ability to dis-
tinguish contrasts in surrounding parts of the visual field, causing
simply "annoyance, or interference with vision." (1) depends
in large part, perhaps entirely, on the absolute brightness of the
area concerned ; ( for upper limit of brightness permissible within
the visual field see other reports in this series) ; on the retinal
area on which the image falls ; and, perhaps, to a small extent on
the condition of adaptation of the eye. (2) depends quite as
much on the condition of adaptation of the eye as on the absolute
THE EFFECT OF GLARE ON VISION IOC»9
brightness of the objects concerned. "Interference with vision"
due to (2) is from three causes:
(a) It is well known that an excessively bright area, even
though small as compared with the whole field, will cause a con-
traction of the pupil, thereby reducing the physical brightness of
the image of the whole field as formed on the retina. Certain ex-
periments seem to indicate, however, that this effect is in part
compensated for by increased visual acuity due to having the
lens stopped down.
(b) The eye media cause a slight scattering of the light from
the excessively bright area, causing the equivalent of veiling glare
over the areas immediately surrounding the bright source.
(c) More important still, the existence of excessively (rela-
tively) bright areas within the field of vision tends to shift retinal
adaptation toward that required for the brighter area. Whatever
the process of adaptation, it is probable that one part of the retina
is affected to some extent by the adaptation of another part. Con-
sequently, or inability to see detail in a dark field in the fore-
ground of which is a bright light source is in part to causes
exactly the same as those which make it impossible to see, at first,
when entering a darkened room from sunlight. That is, it is
simply a matter of adaptation.
The deleterious effects of excessive contrast depend in part on
the relative sizes of the contrasting areas. With large contrasting
areas (brilliantly lighted table top, with remainder of room dim)
re-accommodation both pupillary and retinal is necessary as one
shifts one's gaze from the brighter to the darker area and vice
versa. If this re-accommodation occurs too frequently interfer-
ence with visual functions may result. On the contrary small
"checker-board-like" contrasting areas do not necessitate such re-
accommodation, and from that standpoint are less objectionable.
As studied subjectively, we can divide the effects of glare due
to excessive contrast into two classes:
(1) Ocular discomfort. This manifests itself by a "sandi-
ness" which "soon passes over into a sharp, stinging pain, fol-
lowed by a muscular discomfort, an aching in the ball of the eye
which, if the exposure is continued long enough seems to radiate
to the socket and the surrounding regions of the face and head."
IOIO TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
This discomfort is not felt in the retina as a result of over-stimu-
lation, but in the other parts of the eye.
(2) Simple interference with vision, by reduction of visual
acuity, etc.
Ocular discomfort depends on the intrinsic brilliancy of the
bright area and on its extent. Thus, the ocular discomfort aris-
ing from a 500-watt tungsten lamp within the field of view is
greatly reduced by surrounding the lamp by a suitable translucent
shade. In general, bright areas within the field of view which
leave persistent negative after-images, are to be avoided.
Interference with vision, however, seems to depend on the total
light entering the eye from the bright area. Thus, while a globe
around a 500-watt lamp largely eliminates ocular discomfort, it
does not materially reduce interference with vision, unless the
intrinsic brightness of the area be brought down to the general
level of that in the field of view (under which condition excessive
contrast no longer exists). In this connection it has been shown
that if the interference with vision be expressed as a "blinding
effect," which quantitatively is "the per cent, increased illumin-
ation for equal clearness of vision as compared with conditions
where the blinding effect is absent," then the so-called blinding
effect is proportional to the square root of the candlepower of
the bright area (source) in the field of view.
Protective neutral tinted glasses may be of value in eliminating
ocular discomfort due to contrast glare. They obviously cannot
materially reduce interference with vision, since they simply re-
duce the general level of brightness and therefore of adaptation,
but do not reduce the contrast.
EXCESSIVE EXTRA- VISUAL RADIATION.
In spite of a great deal of experimentation and speculation on
the effect of extra-visual radiation on eye media and the visual
functions, no very definite conclusions have been reached. There
is, for example, much disagreement as to the limits of trans-
parency of the several eye media in the ultra-violet. One ob-
server states as follows :
Cornea : Transparent above 0.295/i, ; opaque below.
Lens : Increasing transparency from 0.350/t to 0.400/i ; com-
pletely transparent above 0.400/x,.
THE EFFECT OF GEARE ON VISION IOII
Vitreous : A 3/16-in. layer shows a broad absorption band
from 0.250/1 to 0.280/1, with a maximum at 0.270.
Another observer states that light wave lengths shorter than
0.320/i cannot pass the cornea. Another states that, with suffi-
ciently intense radiation, lines in the neighborhood of 0.30 are
distinctly visible as lines.
Less work has been done regarding the transmission in the
infra-red region. It is concluded that "the total energy trans-
mitted through the several layers of eye media, as they exist in
contact with each other, is about the same as that transmitted
through an equal quantity of water."
Ultra-violet radiation may be visible indirectly, by the fluor-
escence which it produces in the lens (and retina).
Over-exposure to ultra-violet radiation produces a "burn."
After a time, perhaps a few minutes, frequently many hours,
there results pain in the eyes, a deep-seated itching, sensitivity
to light, twitching and swelling of the lids. There is strong con-
traction of the pupil and conjunctival discharge. Examination
shows a contraction of the visual field, reduction in visual acuity
and partial or total loss of dark adaptation. Complete recovery
requires several days. In the more severe cases there may be
permanent reduction in visual acuity. One authority states that
the source of the trouble comes from rays shorter than 0.330/*.
Others seem inclined to put the limit somewhat lower.
No definite statement can be made regarding the effect of
infra-red radiation. In general, however, no deleterious effects
comparable to those due to ultra-violet radiation seem to have
been observed. Even in the case of radiation comparatively rich
in infra-red, it is probable that the absorbing power of the an-
terior eye media sufficiently protects the sensitive retina from
injury, except for the most intense and unusual cases.
It is probable that the harmful effects of extra visual radiations
on the retina cannot be expressed completely in terms of the
wave length and intensity of the radiation concerned. The con-
dition of the eye is a very important factor. For example, if the
eye be dark adapted, just as it is more sensitive to visible radi-
ation, so also it may be more sensitive to the effect of ultra-violet
radiation. It is possible that, by reason of being light adapted,
IOI2 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
the retina is protected from the ultra-violet of daylight, while
with the eye partially dark adapted there is insufficient protection
against the smaller amount of ultra-violet contained in artificial
illuminants. In other words, the mere fact that artificial illum-
inants contain proportionally less ultra-violet than daylight is not
of itself a proof that the ultra-violet of modern light sources is
not harmful. The effects of ultra-violet radiation are probably
due to atomic disturbances ; i. e., are chemical in nature. Since
the chemical effect of radiation is selective, the intensity of the
disturbances due to this cause are a function not only of the
energy contained in the radiation itself, but of the character of
the receiver. We may not be able to specify structurally, wherein
the dark adapted eye differs from the light adapted eye, but func-
tionally we know that a great difference exists.
It is safe to say, in spite of our lack of knowledge of the nature
of the harmful effects of radiation, that where the eye is exposed
to radiations known to contain relatively large amounts of extra
visible radiation, one should use protective glasses which cut off,
so far as possible, the ultra-violet and infra-red. Except for
esthetic reasons there is no particular harm in using a glass which
cuts off also some of the visible spectrum, if that be necessary to
insure complete elimination of the extra visual content.
VEILING GLARE AND FLICKER.
These conditions which cause ocular discomfort are dismissed
together, because it is probable that a large part of the source
of trouble is not directly physiological but is to a certain extent
psychological. The connection between the eyes and the various
bodily functions is well known. To a layman, this indicates that
a comparatively slight cause may seriously disturb the "equili-
brium" existing in our ocular apparatus. Thus, there are twelve
muscles which rotate the eye-ball in its socket. Each eye must
be so oriented that the image viewed will fall on exactly the same
part of each retina — an adjustment which must be made with the
highest precision. Evidently, this requires "a most complicated
and delicately balanced set of muscles and nervous connections —
and a small but persistent disturbing circumstance may work not
only great discomfort, but in extreme cases, such confusion of the
various eye movements as to make vision well nigh impossible."
THE EFFECT OF GLARE ON VISION IOI3
When we consider the still more delicate mechanisms which
operate the iris and the lens, it is safe to say that any condition
which, however little, interferes with comfortable vision must,
if continued, result in ill effects. Even were the data available,
it would be beyond the scope of the present report to analyze the
various conditions coming under the above head.
Veiling glare (see examples mentioned in other reports) re-
sults in insufficient contrast. "The seeing is bad." One feels
(perhaps unconsciously) an annoyance at not being able to dis-
tinguish clearly, and with ease, detail in the field of view. These
are possibly efforts to refocus. The annoyance, mental and ocu-
lar, causes a strained condition in all parts of the visual apparatus,
so that, even though the brightness be within the limits of toler-
ance, and the radiation reaching the eye contain no specifically
harmful component, serious harm of a more or less nervous
nature, may result.
The same remarks apply to flicker — either in brightness or in
space. The general dissatisfaction at not being able to see clearly
is of itself largely the cause of the ocular discomfort. In dis-
placement flicker there is the added strain on the external eye
muscles, and in brightness flicker a corresponding strain on the
iris due to constant attempts at pupillary adaptation, and if the
range of brightness be extreme, there is continual retinal adapta-
tion.
"It is a great though often forgotten physiological law that any
organ, exercised within its limits, tends to increase in power, and
facility, while if overworked it becomes less and less able to do
any work at all. If a man habitually uses his eyes in strong
lights he decomposes his visual purple faster than it can be re-
generated. If he uses his ciliary muscles without rest, day after
day, they begin to break down under the strain and become fa-
tigued even by short periods of use."
Permissible fluctuations in brightness depend on the adaptation
of the eye and on the time rate of change of brightness. Thus
10 per cent, "sine- wave" changing in brightness with a period of
several seconds would not be so objectionable as an abruptly
alternating increase and decrease of brightness of the same period
and amount.
IOI4 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
When the fluctuations of brightness are sufficiently high so as
not to give the sensation of flicker, common experience seems to
indicate that there is no harmful effect. It has been shown that
the optic nerve can transmit a flickering sensation whose fre-
quencies are far higher than those, (i. e., 40 or 50-light cycles
per second) at which vision becomes continuous. This indicates
that the damping out of the flicker must occur in the retinal
processes, and hence there can be no reflex excitation of the pupil
or other ocular apparatus whose functioning depend on light
sensation.
Nelson M. Black,
J. R. Cravath,
F. H. Gilpin,
M. LUCKIESH,
F. K. RlCHTMYER,
F. A. Vaughn,
P. G. Nutting, Chairman.
luckiesh: yellow light 1015
YELLOW LIGHT.*
BY M. LUCKIESH.
Synopsis: A discussion of the importance of color in lighting and
vision would be too extensive to be treated in a single paper. However,
inasmuch as most artificial illuminants are decidedly yellow as compared
with daylight and as yellow light has some distinctly different properties
as compared with many other illuminants, a brief discussion of its place
in lighting is presented. The knowns and unknowns, and the various
opinions regarding yellow light are discussed briefly with respect to
visual acuity, glare, fatigue, penetrating power, and esthetic value. The
procedure involved in altering the light from tungsten lamps to a match
with the light from the kerosene flame and old carbon incandescent lamp
is presented together with the resultant efficiencies of the altered light
for tungsten lamps operating throughout the extreme present range of
luminous efficiencies. The error usually made in attempts to simulate
the color of the older illuminants by means of screening tungsten lamps
with yellow filters is pointed out, and illustrated by a comparison of the
ideal transmission screens for accomplishing this purpose with ordinary
amber glass of various densities which is usually used.
The importance of the color of illuminants and their surround-
ings has become very evident to the lighting expert. In fact color
is so influential in lighting and vision that certainly the problems
would often be extremely simplified if color-vision ceased to exist.
Yet few persons realize that the ability to see color complicates
the study of lighting and vision very much. A treatment of the
subject of color in its relation to lighting would be far beyond
the scope of a brief paper, but inasmuch as the majority of arti-
ficial illuminants are yellowish in color, yellow light will be
briefly discussed. There are many unsolved problems pertaining
even to this narrowed field as will be seen by the confused state
of affairs. Any color phenomenon is so complicated that the
chief difficulty in interpreting observations lies in the absence of
properly recording or weighing all the influential factors found in
a given case. Too often matters of taste are construed as gen-
eral facts. The physical problems are usually easy to solve. The
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, 191 S-
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
12
IOl6 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
physiological and psychological problems are more difficult to
study owing to the vagueness of the criteria but these problems
are certainly capable of solution. However, the problems which
involve merely the esthetic taste are indeterminate. An attempt
will be made briefly to point out the knowns and unknowns and
to discuss the opinions and conclusions of various observers re-
garding those phenomena which are of chief interest in a discus-
sion of yellow light.
Visual Acuity. — Some years ago it was shown that mono-
chromatic light was superior to light of an extended spectral
character for the perception of very fine detail. An investiga-
tion1 showed that monochromatic light near the middle of the
spectrum, namely yellow light, was superior for the perception
of fine detail to monochromatic light of any other wave-length.
More recently the author2 has investigated visual acuity in day-
light and ordinary tungsten light. This problem has been studied
under various conditions in connection with other work with the
general result that visual acuity was found to be practically the
same under equal intensities of illumination for these two illum-
inants. These tests were made on fine parallel lines at the thresh-
old of discrimination. In some of the work by the author and
others another criterion was used, namely that of equal read-
ability or clearness of a page of type. This latter criterion ap-
proaches more nearly to the predominating condition found in
practise and has proved to be sufficiently definite to commend its
use in practical investigations. For instance in reading, the char-
acters are recognized in groups and the eye is not focused on in-
dividual letters but travels across a page in a series of jumps.
Even though the eye did examine each letter or portion of a letter
the illumination is usually sufficiently high so that the size of the
detail is far above the limits of discrimination.
Owing to the fact that yellow paper is often declared to be
"easier on the eyes" it was thought of interest to ascertain if there
was an appreciable difference in visual acuity when fine lines
were viewed against backgrounds of white and yellow copy paper.
1 I,uckiesh, M., The Dependence of Visual Acuity on the Wave-Length of I,ight;
Elec. World, 58. P- "32. 19"-
The Influence of Spectral Character of I,ight on the Effectiveness of Illumination;
Trans. I. E- S., vol. 7. P- i35, 1912.
* I<uckiesh, M., Visual Acuity in White I,ight; Elec. World, Dec. 6, 1913.
luckilsh: yellow light 1017
The illuminant was artificial daylight of approximately the same
spectral character as noon sunlight. The reflection coefficients
of the white and yellow papers for this illuminant were 0.77 and
0.69 respectively. Under equal illumination visual acuity was
found to be practically the same with a slight tendency to be bet-
ter with the yellow copy paper as a background. When the back-
grounds were equally bright visual acuity appeared to be slightly
but definitely higher with the background of yellow copy paper.
The illumination used varied from 3 to 10 foot-candles. It should
be noted that this paper was a pale and unsaturated yellow in
color. Although there was no appreciable difference in acuity
when the two backgrounds were illuminated to equal flux den-
sities it is apparent that the light reflected from the yellowish
paper, in which the blue and violet rays were somewhat sup-
pressed, showed a slight advantage per unit of brightness over
that reflected from the white paper in respect to defining power.
This does not necessarily indicate that the unsaturated yellow
light was better for revealing fine detail than any other unsat-
urated color, although other evidence points to this conclusion.
Further, with a given illuminant such as the light from a tungsten
lamp, apparently little advantage is gained in visual acuity by
screening out some of the visible rays of short wave-length. If
this screening were carried further possibly some advantage
might appear. It appears quite likely that, at the higher illum-
inations where visual acuity decreases slowly with decreasing
illumination, the reduction in visual acuity due to decreased il-
lumination, which is the result of the screening process, would
be more than overcome by the increasing definition due to the
approach toward monochromatism of the light passing through
the screen. This point is open to further investigation.
Glare. — The opinions regarding the relation of the color of the
illuminant and glare are quite conflicting. This state of affairs
is no doubt largely due to the indefiniteness of the criteria and
the lack of an approved method of measuring the vague con-
dition known as glare. The opinions that have been expressed on
this point are usually associated with headlights. It is strongly
asserted by some that a yellowish headlight is less glaring than
a white one. While the author does not wish to be understood
IOl8 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
as supporting this conclusion it has often appeared to him that
a greenish-yellow headlight which was experimented with con-
siderably, appeared to be noticeably less glaring than a 'white'
light without the greenish-yellow screen, the units being of equal
wattage. The greenish-yellow screen, however, absorbed about
25 per cent, of the total light which was emitted by the tungsten
lamp used.
On the other hand others have strongly asserted that yellow,
orange and red rays contribute more to the production of glare
than the visible rays of shorter wave-lengths. In fact the ideal
illuminant according to these observers is one that has even less
of the yellow, orange and red rays than daylight. However, until
more convincing evidence is submitted this question is un-
answered.
Yellow and yellow-green glasses are worn considerably for
protecting the eyes from the glare of daylight. That such glasses
reduce glare is quite apparent especially when the eyes are called
upon to perceive fine detail. In the case of outdoor target-
shooting such glasses have proved very helpful; however, in
such cases the decrease in glare is not due, predominantly at
least, to any inherent virtue in the yellow or yellow-green light,
but is due chiefly to the great reduction in brightness of the broad
expanse of visible blue sky and the accompanying decrease in
the luminous flux entering the eye. The author has suggested
the use of a greenish-yellow light for illuminating indoor rifle-
ranges owing to the fact that for equal brightnesses of the targets
and their surroundings (and therefore perhaps approximately
equal conditions of glare) the targets can be seen more clearly,
the increased definition being due in this case to the less extended
spectral character of the light. No definite data is available from
such installations. Protecting glasses will not be effective in the
same manner indoors as outdoors, owing to the absence of a
broad area of high brightness which is present in the latter case.
When yellow or yellow-green glasses are used for distant vision,
with or without field glasses, the increase in the clearness of de-
tails is quite apparent. One reason for this is the partial elim-
ination of the bluish haze which is more or less effective in
obliterating distant details. Some of these effects are not directly
LUCKIESH : YELLOW LIGHT IOIO,
connected with the problems of lighting but nevertheless are
often confused and misinterpreted.
Some time ago Dr. P. W. Cobb showed that a bright light
source in the field of view was glaring even when the image of
this source fell on the blind spot of the retina. He attributed the
glare due to scattered light in the eye. It has been suggested that
blue light might be more glaring than yellow light because of
the greater scattering of the blue rays by fine particles as dis-
cussed later. However, diffusing media differ in their selective
scattering of rays of light and little is known about the selective
scattering of the sclerotica or white exterior coat of the eye-
ball.
The advantage of using yellow or yellow-green glasses has
been shown elsewhere.3 An acuity object was set up on a clear
day in the shade of a building in such a position that a large sky
area was visible to the observer. Visual acuity readings were
made as rapidly as possible and after three minutes had elapsed
yellow-green glasses were quickly placed before the eyes and the
readings were continued. At the end of three minutes these
glasses were removed and readings were made as before. At the
beginning of the observations only a slight sensation of glare was
experienced ; however, as soon as acuity observations were begun
the glare became very evident and rapidly grew painful. Acuity
was always better when the colored glasses were before the eyes
and during the latter part of the experiment, which lasted 18
minutes, it was indeed a great relief to wear the yellow-green
glasses. The absorption coefficient of these glasses was about 50
per cent, yet acuity was better with this reduced illumination than
with the total light and the discomfort due to glare was practi-
cally eliminated. This experiment showed conclusively the re-
duction of glare attending the reduction in the brightness of the
sky area.
The foregoing provides an example of the ease with which
confusing conditions are brought about. It might be argued
that the decrease in the amount of blue light due to a reduction in
the brightness of the sky area was responsible for the reduction
of glare. However, it is quite certain that this excessive glare
* I,uckiesh, M., Safeguarding the Eyesight of School Children; Trans. I. E. S., p. 181,
No. 2, 1915.
1020 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
was due to the broad expanse of bright sky in the visual field
and was not related appreciably to the color. As previously
stated there are no definite data available relating to glare and the
color or spectral character of the illuminant.
Fatigue. — Here again definite data are lacking for quite the
same reasons as found in the measurement of glare, namely the
vagueness of the condition and the criteria and the absence of
an approved and thoroughly tested method. It is perhaps safe to
state that there is a general opinion that ordinary artificial light
is more productive of fatigue than ordinary daylight. The author
is inclined to believe that sufficient weight has not often been
given to the fact that artificial light is usually judged after the
eyes have done a day's work under daylight. It has been con-
tended that the greater energy absorption in the eye media4 per
unit of light for ordinary yellowish artificial illuminants than
for daylight accounts for eye-fatigue under artificial light. Little
account seems to have been taken of the much greater intensi-
ties of illumination usually experienced in daytime. If this con-
tention is correct there should be plenty of evidence of eye-
fatigue due to absorption of energy in many cases of daylighting.
Inasmuch as this point has not been proved and as there are no
experimental data available that throw much light upon the sub-
ject, it is futile to discuss it further.
It has been contended5 that yellow and orange lights at high
intensities are more fatiguing than green and grenish-blue lights.
It has been suggested by some that this result obtains because the
yellow rays are more effective in bleaching the visual purple than
rays of other wave-lengths. There is much to be learned about
this process and several problems must be investigated before
such a conclusion is tenable. For instance, the relation of the
bleaching action to the amount of light-sensation produced and
to fatigue must be known before such a contention can be con-
sidered more than a hypothesis.
The statement is often made that yellow light is "easier on
the eyes" than white light. Usually this is applied to the use of
yellow paper; and, based on this premise, certain books have
4 Luckiesh, M., Radiant Energy and the Eye; Elec. World, Oct. 25, 1913.
Energy Density in the Eye-Media; Elec. World, 1915.
6 Steinmetz, C P., Radiation, Light and Illumination; 1909, p. 265.
luckiesh: yellow light 1021
been printed on yellow paper. There are so many variables that
it is impossible to draw definite conclusions from the available
data. However, it is well to distinguish between the two con-
ditions, namely, black type on a yellow paper illuminated by
white light and black type on white paper illuminated by yellow
light. In general there will be a difference in the contrast ratios
between the type and backgrounds in the two cases. The ink may
be assumed to reflect light non-selectively and therefore, for equal
brightnesses of the type in the two cases, the brightnesses of the
backgrounds, one of which selectively reflects light, will be un-
equal. The contrast ratio is probably of some importance from
the standpoint of fatigue, but there are no data available regard-
ing this point.
The author has used artificial daylight for several years for
desk lighting and it has been his experience that it is less fatigu-
ing than the light from a tungsten incandescent lamp. This is
especially evident when the daylight must be reinforced by ar-
tificial light. This experiment was carried further by using
clear tungsten lamps and tungsten lamps with medium and dense
yellow bulbs for several hours of reading on a great many even-
ings. It is certain that the deep yellow light was more fatiguing
than the light from a clear tungsten lamp and that the latter
seemed to be more fatiguing than the daylight. Another observer
drew the same general conclusions. The experiments were made
with the yellow lamps versus the clear lamps in the evening, but
the comparisons of the artificial daylight and tungsten light were
made in daytime under ordinary working conditions. The light-
ing conditions such as the distribution of light, position of the
book and observer, etc., were such as would be termed satis-
factory. It is recognized that such experiments are not of the
character that would be pronounced conclusive, but it appears
that such data should be gathered and recorded. As long as a
simple method for testing eye fatigue is unavailable such ob-
servations as noted above must govern our practise and in all
events they will be available for future summaries.
PENETRATING POWER.
Inasmuch as blue rays and others of short wave-length
are scattered more than the rays of longer wave-length it is in-
1022 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
teresting to consider the penetrating power of yellow light as
compared with that of other lights. It is well known that smoke
consisting of fine particles appears bluish in color while its
shadow on a white surface is of a reddish hue. The setting sun
appears red owing to the partial absorption of the visible rays
of short wave-lengths by the smoke, dust, etc., in the atmosphere.
This absorption is produced largely by scattering the blue rays
more than the rays of longer wave-length with the result that the
skylight, which is scattered sunlight, appears predominantly blue
in color. In the same manner the familiar haze in the distance
appears blue. It is thus seen that the yellow light will penetrate
through a greater thickness of ordinary atmosphere than white
or bluish light. Obviously deep yellow and red lights if they
could be produced at a high efficiency would be quite satisfactory
for signals that must penetrate a dust and smoke laden atmos-
phere. In experiments conducted on a clear night it has been
found6 that there was no difference in the penetrating power of
tungsten and carbon incandescent electric lights for distances of
a mile.
In the case of headlights another condition is of interest,
namely that when the observer is behind the headlight. In this
case, the condition is different from that of an observer in the dis-
tance trying to distinguish the signal light. An automobile or
locomotive driver uses the light for illuminating the pathway and
if a considerable portion of the light be scattered by fog, smoke,
or dust, it should be more difficult to see through the illuminated
veil than in the case of little or no scattering of light. In fact,
the reduction in the ability to see is very likely due more to this
luminous veil than to the actual loss of light in the projected
beam. This condition is reproduced by painting a screen door
white and attempting to see beyond it. It is well known that it
is difficult to see into a room when such a screen is highly illum-
inated by daylight on the side toward the observer. Owing to
the fact that visible rays of short wave-lengths are scattered
more than the yellow, orange and red rays, it appears that the
luminous veil in an atmosphere laden with fog, smoke, or fine
dust would be less apparent and less liable to obscure vision in
6 Paterson and Dudding, Visibility of Point Sources, National Physical laboratory,
England; Abstract in Elec. World, 1913, vol. 67, p. 266.
luckiesh: yellow light 1023
the case of a yellow illuminant than in the case of one contain-
ing a relatively greater amount of rays of the shorter wave-
lengths. Such experiments are difficult to perform owing to the
impossibility of obtaining constant conditions out of doors and
to the absence of a simple and rapid method for making the
observations. However, the author experimented with tungsten
lamps in automobile headlights using a greenish-yellow glass over
one headlight and a clear glass over the other. On several foggy
nights the experiments were made and although the screens were
used interchangeably on the two lamps the four observers con-
cluded that distant objects in the fog were more easily seen by
means of the greenish yellow light notwithstanding the fact that
the luminous intensity of this beam was 25 per cent, lower than
that of the 'white' beam through the clear screen.
Based upon the forgoing principle several different types of
headlights have been constructed by various companies. These
include gold-plated reflectors, greenish-yellow glass reflectors
backed with a silver coating, yellow-green bulbs for tungsten
lamps, and greenish-yellow lenses in the aperture of the re-
flector. It appears that the latter scheme has all the advantages
possessed by the others and the additional advantage of sim-
plicity. Of course there may be cases where a glass screen can
not be used in the aperture, such as in the extremely powerful
searchlights. In such cases the observer could wear the screens
before his eyes.
The phenomenon known as the Purkinje effect has often been
misinterpreted in considering the penetrating power of illumin-
ants. It is true that at low intensities of illumination the visible
rays of short wave-lengths possess a relatively greater illumin-
ating value than the rays of longer wave-lengths, as compared
with their relative values at high intensities. This fact is per-
haps worthy of attention, but it should be noted that the Purkinje
phenomenon is usually studied with the entire retina dark adapted.
This is not in general the condition found in practise because the
foreground, especially from the point of view of an automobile
or locomotive driver, is usually of brightnesses well above the
Purkinje region. Some investigators have found the Purkinje
phenomenon to be much less marked in the case of the photo-
metric field being surrounded by a field of moderate brightness.
1024 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
It is interesting to note that the visibility of point sources of
light in clear atmosphere has been shown6 to vary directly as the
candlepower and inversely as the square of the distance. Further,
in the case of signals it must be remembered that the central
region of the retina, where objects are seen clearly, is more sen-
sitive to yellow light than to blue light.
ESTHETIC VALUE.
The esthetic value of colors is quite a matter of taste; there-
fore it is not surprising to find a diversity of opinion. For this
reason it is difficult to discuss this phase of the subject. Too
often the illuminating engineer fails to distinguish between mat-
ters of taste and scientific facts that are not affective in nature.
So that it appears profitable to discuss this subject briefly in order
to emphasize this point. The history of the esthetic value of
yellow is interesting as it is for colors in general. It is of par-
ticular interest inasmuch as artificial illuminants were for many
years of a yellowish hue and even to-day most of the illuminants
that are used where the esthetic taste is important are quite
yellow as compared with daylight. While there are problems
pertaining to the affective value of colors awaiting solution, it
appears to the author that the chief object of the lighting expert
in dealing with the esthetic side of color in lighting should be to
ascertain, and satisfy if possible, the esthetic taste of his client
rather than his own. It is the client who must be satisfied and
it is the client who is obliged to live amid the surroundings whose
appearance is largely under the control of the lighting specialist.
Experience shows that illuminants of many tints find a place in
lighting owing to the diversity of taste which actually exists.
If a person interested in lighting prefers the "warmer" tints of
the older illuminants he should recognize that this is a question of
personal taste and should not enforce upon others a condition
which is strictly a matter of taste. Likewise those who believe
that modern illuminants should be altered in the other direction
because they prefer artificial daylight should take care that they
distinguish between those cases which require light of a daylight
quality for scientific reasons and those which are governed only
by the esthetic sense.
« Paterson and Dudding. Visibility of Point Sources, National Physical laboratory,
England; Abstract in Elec. World, 1913, vol. 67, p. 266.
luckiesh: yellow light 1025
There are many interesting, conflicting, and amusing state-
ments to be found regarding the psychological (and physiological)
influence of color. It is quite permissible to express personal
opinions and convictions regarding the psychological influence
of color, but care should be taken to label these "personal convic-
tions" in order that those less familiar with the subject may not
take the statements too seriously and assume that they are gen-
erally applicable. A common mistake is made in expressing a
conclusion involving psychological influence of a certain condition
of lighting and ascribing a reason which can be shown to be
unjustified. It has been stated by a lighting specialist that the
"white" light of the tungsten lamp caused persons to be depressed,
to have a headache or to have the blues. It is a remarkable fact
that those persons enjoy life at all considering that they are com-
pelled to live in daylight for a large portion of their time. Of
course the appearance of a color is very largely influenced by its
environment and contrast is an important factor. How much a
purely imaginary contrast can effect personal taste the author is
unable to state; but, if the person who is depressed by tungsten
light owing to its "whiteness" is mentally comparing its color
with that of the carbon lamp or another old illuminant, it is quite
likely that the tungsten lamp appears unduly white. But why
should the older illuminants be taken as the standard for com-
parison? If that person should compare carbon and tungsten
lamps side by side with daylight relatively little difference will be
seen between the colors of the kerosene, carbon and tungsten
lights. It is strange indeed to hear so little complaining regard-
ing the unesthetic color of daylight. However, influenced by
these various appeals for "warmer" illuminants, one is often
inclined to believe that the Creator made a mistake in designing
the first and most universal illuminant. Perhaps He designed the
best utilitarian illuminant leaving it to man, as he rose in the
scale of intelligence, and developed an esthetic sense, to provide
his own luxuries.
In a recent paper in the Transactions the use of amber glass
was very much in evidence for altering tungsten light to a
"warmer" tint. Amber glass will not alter tungsten light to
match any of the older illuminants and while it may be preferred
1026 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
by many persons it has a greenish tinge that is objectionable to
many. Thin amber glass is nearly a lemon yellow and the dense
specimens become less greenish when viewed in tungsten light,
but at no density will the ordinary amber glass match any of
the older illuminants. Therefore, if light of an amber color is
preferred it is not because it imitates the color of older illu-
minants. Here it may be of interest to refer briefly to some
experiments conducted in a study of color preference.7 A group
of fifteen fairly saturated colored papers (representing the whole
range of the spectrum) each 4 inches (10.16 cm.) square, were
presented to fifteen observers who were instructed to choose
the colors in the order in which they preferred them. Among
other instructions each observer was asked to choose the colors
for color's sake alone by isolating each color in his mind. In fact,
he was told to "live" and to "see" each color individually until he
was prepared to make his choice. Both in tungsten light and
daylight (the separate experiments being conducted usually sev-
eral weeks apart) the lemon yellow ranked last and the more
reddish yellows ranked about midway in the preference order.
The lemon yellow was placed last in the preference order by
nearly every observer. These data are not presented as proof
that the average person does not like an amber color because it is
a long step from this experiment to lighting conditions, but rather
to illustrate that the esthetic or affective values of colors can be
studied with groups of persons.
The author has experimented with clear tungsten light, arti-
ficial daylight, rose, yellow, blue, red, and amber lights in the
home, and while some of these results are outside the scope of
this paper, it may be of interest to record his personal con-
clusions. Clear tungsten light was found to be satisfactory in
most cases when the glass shade or accessory was of a yellowish
tint. The light itself was satisfactory as far as the appearance of
most objects was concerned. Especially in a shower over the
dining room table it was satisfactory but largely due to the fact
that the glass shades which concealed the lamps were a deep
yellow in color providing a low intensity yellow light for il-
luminating the walls and ceiling and permitting unaltered light
to illuminate the table. The artificial daylight lamps were pleas-
7 I/uckiesh, M., Color and Its Applications, Fig. 77; Scientific American, June 26, 1915.
luckiesh: yellow light 1027
ing in the same fixture and also in a reading lamp with a yellow
silk shade the direct light being unaltered in color. In a white
semi-indirect bowl in the living room slightly rose-tinted lamps
were used for several months. These were found to be definitely
unrestful and somewhat irritating. The yellow lamps which were
carefully made to match a kerosene flame were the most satis-
factory for the general illumination in the living room for con-
versational purposes, but not for reading. The deep blue light
which was used to illuminate the ceiling of the dining room in
order to roughly imitate out of doors was quite depressing. The
red, as is commonly experienced, was highly unsatisfactory for
general illumination even at low intensity and low saturation.
The amber light was not as satisfactory as the unsaturated yellow
which simulated the kerosene flame. These conclusions were
quite definite in all these cases and were arrived at through many
experiments and many months of observation under ordinary
conditions in the home. It should be noted that the rugs and
paintings in the room lost much of their beauty under the yellow
illuminants which suggested the possibility of using tungsten
lamps with both clear and yellow bulbs on separate circuits. This
scheme was tried and has been used for a year with considerable
satisfaction.
SIMULATING OLD ILLUMINANTS.
The present efficiency of illuminants makes it possible to vary
their color to suit the requirements by the use of colored screens
and yet enjoy the advantage of a fairly high efficiency. The
quality of the tungsten light has been altered to match in spectral
character various kinds of daylight. Owing to the fact that many
have expressed a desire to simulate the color of the older illum-
inants, considerable attention8 has been given to this subject.
The transmission of ideal screens for converting the light from
vacuum tungsten lamps of various luminous efficiencies to the
same spectral character of the old carbon incandescent lamps
(3.1 watts per mean horizontal candle) and of the kerosene flame
have been computed and the resulting luminous efficiencies have
been determined. In Fig. 1 Curve Or represents the transmission
8 I,uckiesn, M., Simulating Old Illuminants; Elec. Review and W. E., July 24, 1915,
p. 161.
1028 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
of the ideal screens for total light for converting the light from
vacuum tungsten lamps operating at various efficiencies into light
of the same spectral character as that of the carbon incandescent
/<x>
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Fig. i. — Showing the transmission of colored screens for use with the vacuum tungsten
lamps for simulating old illuminants; also showing the luminous efficiency of the
altered light.
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Fig. 2.— Data similar to that in Fig. i but for the gas-filled lamp.
lamp. Curve Kt is a corresponding curve for the ideal screens
which convert the light from vacuum tungsten lamps into light
of the same spectral character as the kerosene flame. On com-
luckiesh: yellow light
1029
bining the transmission of the ideal screen in any case with the
luminous efficiency of the unscreened illuminant, the luminous
efficiency of the altered light is obtained. Curve CE represents
the final luminous efficiencies of the vacuum tungsten lamp after
it has been screened to match a carbon lamp in color. KE shows
a similar data when the tungsten lamp has been screened to match
the kerosene flame. In Fig. 2 the corresponding data are given
for the gas-filled lamp.
In Fig. 3 curve C represents the spectral transmission curve of
the ideal screen for altering the light from a vacuum tungsten
lamp, operating at 7.9 lumens per watt, to a spectral match with
ary
J6/js*-Le"fM
Fig. 3.— Ideal screens for tungsten lamp (vacuum) operating at 7.9 lumens per
watt compared with common amber of various densities.
the light from the carbon incandescent lamp under consideration
between 0.40/i and 0.70/1, the transmission being assumed to be
100 per cent, at 0.7071, the practical long-wave limit of the visible
spectrum. Curve K is a similar curve of an ideal screen for
matching the spectrum of the kerosene flame. Curves C and K'
in Fig. 4 are similar curves of corresponding ideal screens for the
gas-filled tungsten lamp operating at 22 lumens per watt. Similar
computations have been made for tungsten lamps operating at
various efficiencies, which data have been used in plotting the
curves shown in Figs. 1 and 2.
In producing practical colored screens for the foregoing pur-
IO3O TRANSACTIONS OF II^UMINATING ENGINEERING SOCIETY
poses the obvious beginning is to use a yellow pigment. No per-
manent pigment has been found which alone will suffice. This
is not surprising to one familiar with coloring elements, but it has
not usually been recognized in practise. Most so-called yellow
pigments have a greenish tinge in the lesser densities and the
author is not aware of any permanent yellow pigment that matches
a spectral yellow in hue, or that at any density will, when used
with the tungsten lamp, match the unsaturated yellow of the old
illuminants. Usually a pigment which is given the name of
amber is considered satisfactory. Of a number of yellow pig-
ments examined (and these represent perhaps all the permanent
0.+&U.
t66v&- /-<~nfM
Fig. 4. — Ideal screens for tungsten lamp (gas-filled) operating at 22 lumens per
watt compared with common amber of various densities.
yellow pigments) none was found to be satisfactory alone. An
example which is approximately representative of this group of
yellow pigments is shown by the so-called amber glass of four
different densities in Figs. 3 and 4. The numbers on the curves
represent the relative amounts of coloring matter present per unit
of surface area of the amber glasses. In general the glasses are
seen to transmit green rays too freely. In order to make this
point clear the spectral transmission curves of the ideal screens
C and K in Fig. 3 have been plotted equal to unity of all wave-
lengths in Figs. 5 and 6 respectively, and the transmission of the
amber glasses were made equal to unity at o.yoyi, the practical
LUCKIESH : YELLOW LIGHT
IO3I
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Fig. 5-— Showing the ratio of transmission of amber glass (various densities) to that of
an ideal screen for converting the light from a tungsten lamp operating at 7.9 lumens
per watt to the same spectral character as that from the carbon lamp.
&>o
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Fig. 6. — Showing the ratio of transmission of amber glass (various densities) to that of an
ideal screen for converting the light from a tungsten lamp operating at 7.9 lumens per
watt to the same spectral character as that from the kerosene flame.
13
1032 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
limit of the visible spectrum. It is thus seen that no density of a
so-called amber glass will suffice for the purpose under consid-
eration.
These curves for an average yellow pigment have been pre-
sented to illustrate that it is not an extremely simple matter to
simulate the color of the older illuminants by using colored
screens with tungsten lamps. However, inasmuch as the re-
quirements do not demand more than a close approximation, one
familiar with pigments and color mixture readily can produce a
proper coloring. The match can be subjective if the spectral
character of the altered light does not vary too much from the
illuminants to be matched. Satisfactory colorings have been made
for matching the kerosene flame by means of the tungsten lamp
and on viewing this lamp in comparison with the common amber
lamps the truth of the foregoing is strikingly evident. That is,
the ordinary amber lamps appear very different from the unsatu-
rated yellow of the properly colored lamps.
It has long appeared to the author that illuminating glassware
which largely is practically colorless, if properly tinted an un-
saturated yellow instead of the common greenish-yellow, would
meet with the approval of many users. For instance, the ap-
pearance of a semi-indirect bowl of the proper tint would satisfy
the esthetic taste of those who desire the "warmer" tints, and if
the walls and ceiling were properly tinted clear tungsten lamps
would be satisfactory. It has been shown9 that the color of the
surroundings alter considerably the useful light by selective re-
flection. In fact it was shown that with the so-called indirect
and semi-indirect systems a yellow tinge in the color of the walls
and ceiling altered the tungsten light which reached the useful
plane to a yellowish hue more saturated than that of the older
illuminants. This alteration by selective reflection can be utilized
in many cases of so-called indirect and semi-indirect systems and
in the case of the latter the bowl can be properly tinted. In the
case of direct units it is more difficult to obtain the "warmer"
light without coloring the lamp. However, as shown in the case
of the shower, if the shades are deep enough and of the desired
color the results can be made pleasing. However, it is not the
» IyUckiesh, M., The Influence of Colored Surroundings on the Color of the Useful
Light; Trans. I. E. S.
LUCKIESH : YELLOW LIGHT IO33
intention of the author to discuss fully this phase of the subject.
An attempt has been made to point out briefly the place of
yellow light in the problems of lighting and vision. There are
many conflicting opinions and a lack of data on some questions.
The chief reasons for the confusion appears to be due to misin-
terpretation of results by the lack of careful analysis of the con-
ditions. It has appeared worth while to record the results that
have been obtained, to summarize the opinions and conclusions
of others and to discuss briefly the theory underlying certain
phenomena. Many of the questions involved in the foregoing
discussion have arisen from time to time and it is to be hoped data
will be presented by others which will aid in clarifying the con-
fusion now existing. It is further to be hoped that the illumin-
ating engineer will be more analytical in drawing conclusions and
recording observations concerning such phenomena as are dis-
cussed in the foregoing paragraphs.
OTHER REFERENCES.
LUCKIESH, M.
Color and Its Applications, New York, Chapters VI and XL
Cobb, P. W.
Physiological Points Bearing on Glare.
Trans. I. E. S., 1912, 6, p. 164.
The Psychology of Yellow.
Pop. Sci. Monthly, 1906, 68, p. 456.
Jastrow, J.
The Popular Esthetics of Color.
Pop. Sci. Monthly, 1897, 50, p. 361.
DISCUSSION.
Mr. J. R. Cravath : I am very glad Mr. Luckiesh has ex-
ploded a bomb under a lot of nonsense that has been talked about
matters of color in connection with illumination engineering, and
shown where the line of demarcation is between taste and
scientific fact. There has been a great deal said about color which
is purely a matter of personal opinion.
Dr. J. W. ScherESCHewsky: It seems to me that, consider-
ing the matter on physiological grounds, there can be no reason
whatever for asking for a yellowish tone in artificial illuminants.
The nearer they approximate the spectral composition of day-
1034 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
light, the better they are for seeing purposes. I think possibly
one reason why we have found kerosene light, for instance, agree-
able, is that at the low intensities at which kerosene lights are
usually employed, the eye perhaps finds it a little more able to
adapt itself to the luminous intensity involved. It seems per-
haps— I don't know — that this is a subject for future investiga-
tion. There is some internal evidence to the effect that the
shorter wave-lengths will tend to produce a state of hyperadap-
tation, that they are stimulators of adaptation. That is to say,
when we have high intensities, we will get a little better adapta-
tion to those intensities if the percentage of blue light in the
source approximates daylight. On the other hand, in very high
intensities in which the yellow component is more in evidence,
there may not be that physiological stimulus to complete adapta-
tion which blue wave-length seem to bring forth. On the other
hand, where we use low intensities, as in the case of kerosene
light, the eye is perhaps a little bit more sensitive to the light
under those circumstances ; and consequently with that low inten-
sity, we find the light agreeable to read by; but I think on the
whole that we are advancing toward the natural trend which
illuminating engineering ought to take, where our whole aim will
be to reproduce, as nearly as we can, the natural composition of
daylight and raise the intensity. I cannot see any real object in
trying to produce warm tones except simply the psychological
association with firelight which was the symbol for warmth and
comfort in the early days when men had a much harder struggle
to live than they have now.
Mr. G. H. Stickney: In practical illuminating engineering,
questions relating to the color of light arise in quite a number of
problems. It is not surprising that there is more or less confusion
as to whether the color differences affect the physiological action
of the eyes or the mental processes, especially as both are quite
susceptible to suggestion. This is rather borne out by the dif-
ferences of opinion among different individuals or communities,
while those who are closely associated seem inclined to agree one
way or another.
In street lighting, for example, some people think they can see
much better by a white light than by one having a slightly yellow
YELLOW LIGHT IO35
tint. On the other hand, others claim they can see fully as well
by the yellow tinted light and prefer it on account of its pleasing
color. Personally, I have been unable to discover any apprecia-
ble difference, traceable to color, in the seeing value of light from
the high efficiency incandescent lamps or the white or even
slightly bluish lights. I believe that such differences are more
readily explained by variations in intensity, direction or glare.
Again, we sometimes hear that white light from street lamps
is preferable for use in conjunction with incandescent lighted
show windows. My own observation has been that the most
pleasing effect is obtained when both are approximately the same
color. When two such colors of light are mingled so as to em-
phasize the simultaneous contrast, I have noticed that if the white
light is more brilliant, the yellow light looks dingy; or if the yel-
low light predominates it looks warm and pleasing, while the
white lights appear cold and blue. Still I am not sure but what
there are conditions under which it might be desirable to combine
the two colors of light.
In store lighting we sometimes find a compromise necessary.
White light is unquestionably preferable for the selection of
colored materials for daylight use. On the other hand, most store
managers seem to prefer the appearance of the store under in-
candescent illumination, and even where colored materials are
sold they often consider the warm homelike effect of the yellow
tinted light more important than the degree of color matching
quality obtainable with any practical illuminants.
Another phase of this question arises in connection with head-
lights for automobiles, etc. It has sometimes been thought ad-
visable to use yellow screens in connection with incandescent
headlights to reduce the glare. This, of course, has to be con-
sidered from two standpoints. To the approaching observer
glare does not seem to be reduced to any greater extent than has
the illumination ; on the other hand, to the driver behind the head-
lights there is undoubtedly a reduction of halation especially on
damp or foggy nights. Beyond the reduction of this diffractive
halation, I doubt if there is any advantage to be gained in cutting
down the illumination by the use of any form of color subtractive
screen.
IO36 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
A Member: Some fifteen years ago I carried on a series of
experiments with a view to determining the best light for the eyes,
taking as the criterion, the ease with which reading could be done,
and after going over quite a range of colors, I decided on the
yellow-green. Experiments were carried on in a closed room at
night and with a light source out of the range of vision.
Dr. J. W. ScherEschewsky: I forgot to mention the range
of personal preference of individuals with regard to the refrac-
tion of the eye. It seems to me that the refraction of the eye
often has a marked influence on the kind of light and the kind
of colors individuals prefer. Persons who have a tendency to
hyperopia are naturally inclined to prefer colors at the short end
of the spectrum, whereas myopes prefer longer wave-lengths
which can be focused with greater ease on the retina; so I
think that the preference really lies in the state of refraction of
the eye of the individual concerned.
Mr. W. A. Durgin: If the use of white or yellow light is
only a matter of personal preference, as this paper rather indi-
cates, the immediate problem of light supply becomes a deter-
mination of the present preponderance of that preference. My
personal experience seems to indicate a majority choice of yel-
low light. In the offices of Commonwealth Edison Company of
Chicago, where 1,200 employees work under a distinctly yellow
flux, at least sixty have come forward with expressions of ap-
proval, whereas none has expressed dissatisfaction. This, how-
ever, is only an indication. Widespread observation is needed,
and the accumulation of such preference data should be made a
part of all illumination testing programs.
Dr. Charles P. Steinmetz: The subject matter of Mr.
Luckiesh's paper on the effect of the quality of color on the ease
of the eye is a very interesting one and very well worth careful
consideration and study, especially since the experimental evi-
dence of different observers not infrequently directly contradicts,
and even the conclusions of one and the same observer under dif-
ferent conditions are not infrequently entirely contradictory.
Now the reason, the way I look at it, is, that the easiest light is
the light that is least fatiguing to the eye. Now at times it de-
pends on the conditions, whether fatigue will occur with one
YELLOW LIGHT IO37
color of light or another color. I do not believe there is any par-
ticular color of light which, by itself, is less or more fatiguing
than another, but the question depends entirely on the relation
of the color of the light to the color of the objects which are dis-
tinguished and the purpose for which we desire to distinguish
them. If there is any special quality in the light by itself, we
would naturally expect that in the middle of the spectrum, which
is about between 53 and 54 microcentimeters, the light would be
the easiest. Now then, we use light to distinguish, and where
the observer of the light is to distinguish objects sharply, as for
instance, in reading and calculating and doing exact work, there
naturally that light will be the least fatiguing which gives the
sharpest distinction, that is, which exaggerates contrast ; and that,
indoors, is a short wave light, the white or the bluish green.
Where the purpose is to rest the eye, that is, not to give strong
contrast and thereby irritate the eye by continuously seeing ir-
relevant things, but merely to show enough contrast to be able to
walk around and see the room, as for general indoor illumination,
there the light will be the least fatiguing which reduces the con-
trast. Now you see that depends on whether you arrange your
experiment in trying the restfulness of light under conditions of
exact detail work or under conditions of resting after the day's
work in your room ; obviously exactly opposite conclusions about
the color of the light may be obtained. Furthermore, the restful
light, which reduces contrast so much that when you are nervous
or irritated, you feel that it is restful, will usually be the long
wave-light, yellow or orange-yellow, because the predominant
doors, where the predominant colors are blue and green, the
was pointed out by Mr. Luckiesh is very irritating because it is
intensified by contrast with the different kinds of light; while out
doors, whwere the predominant colors are blue and green, the
short waves, the blue sky is not irritating, while if, under certain
atmospheric conditions you have a yellowish sky, you feel un-
comfortable. You cannot speak of a definite color of light as
having a definite effect, but it is all relative. Monochromatic
light allows the eye to focus, because you get a definite focus,
but where a definite distinction is not wanted, monochromatic
light is not wanted ; otherwise chromatic, light, by distorting the
color effect, is irritating to the eye; it means, in short, that the
IO38 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
effect of color of light, in its effect on the eye, is entirely a relative
condition dependent on the surrounding objects in their color
character and the purposes for which you desire to see.
Mr. M. Luckiesh (In reply) : I gathered together these con-
flicting conclusions with the hope that with closer attention by
lighting engineers the questions will be answered eventually. The
last sentence in the paper brings forth a vital point in future pro-
cedure. There is little to add to the discussions by various
members. I should like to bring out one point in connection with
Mr. Durgin's remarks. He has exhibited here a unit consisting
of amber glass cased with opal glass. When the unit is lighted
the bowl appears a decidedly amber color. He mentioned that
quite a number of employees "have come forward with ex-
pressions of approval wheras none has expressed dissatisfaction."
Inasmuch as only a portion of the light (the direct component) is
altered by the amber glass, I wonder whether the employees in
expressing approval were influenced by the color of the light unit
or the actual color of the light which they use. These are prob-
ably two different colors, the light which they use consisting of
the altered direct component plus the indirect component which
is altered by reflection from the walls and ceiling. I have shown
that the alteration due to colored surroundings is considerable
(Trans. I. E. S., vol. 8, 1913, p. 62). This illustrates a point
from which much confusion may arise. A danger in using the
opinions of laymen is that these opinions may be influenced, as is
possible in this case, by the impressions gained by looking at the
lighting unit instead of through a consideration of the light that
actually reaches their working planes. It may be in this case that
no such errors exist; nevertheless, this is a very common error
among those who use light. In considering this entire subject,
one should be careful to make a complete analysis of the con-
ditions and when using the opinions of laymen, one should be
certain that the opinions are based upon such an analysis. An-
other danger in using opinions of laymen is that there is often a
decided tendency of such observers to form opinions that they
believe are desired by their superiors. These are examples of
pitfalls that are well known and thoroughly considered by the in-
vestigator.
MILLAR: THE EFFECTIVE ILLUMINATION OF STREETS IO39
THE EFFECTIVE ILLUMINATION OF STREETS.*
BY PRESTON S. MILLAR.
Synopsis: This paper mentions the dependence of effectiveness in
street lighting upon municipal appropriations and efficient lamps, but dis-
cusses more particularly those aspects of effectiveness which are dependent
upon skilful utilization of the light to produce the most effective illumina-
tion. There are included a classification of streets, a statement of the
objects of street lighting and the elements of vision under street lighting
conditions. The paper emphasizes three considerations which are some-
times neglected in street lighting discussions; namely, the silhouette effect,
specular reflection from street pavements, and glare. The remainder of
the paper is given over to a presentation of the variables upon which the
effectiveness of street illumination depends, and upon the influence which
each feature of the installation exercises through these several variables.
As a part of this discussion illuminating efficiency values for the several
modern street illuminants are given. The appendix includes statistics and
photographs of some very recent installations which illustrate the latest
trend in street lighting.
Improvement in street lighting involves (i) larger municipal
appropriations; (2) more efficient lamps and accessories; (3)
greater skill in application.
FACTORS INFLUENCING IMPROVEMENTS.
Larger Municipal Appropriations. — The public is gradually
becoming acquainted with the advantages of more liberal use of
light. Use of the streets at night is becoming more general
throughout a greater number of hours. Requirements for good
street lighting are becoming greater as traffic becomes denser and
as traffic speed increases. Also the advertising value of exten-
sively employed light is commanding appreciation in mercantile
lines. These things combined are leading to larger municipal ap-
propriations. Larger appropriations mean betterment in street
illumination because the mere addition of lamps with no increase
in lighting efficiency and no greater skill in application usually
improves conditions. The greatest single obstacle to satisfactory
street illumination is lack of funds.
More Efficient Lamps and Accessories. — The last two years
have witnessed increases of 25 to 50 per cent, in efficiencies of
street illuminants, the gas-filled, tungsten incandescent lamp and
the magnetite arc lamp having progressed contemporaneously.
At the present time in the magnetite lamp of medium and high
* A paper read at a joint meeting of the American Institute of Electrical Engineers
and the Illuminating Engineering Society, at a convention of the former organization
held June 29 to July 2, 1915, at Deer Park, Md.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
IO4O TRANSACTIONS OF* ILLUMINATING ENGINEERING SOCIETY
power, in the gas-filled lamp of low, medium and high power,
and in the flame arc lamp of high power there are available il-
luminants having efficiencies four or five times greater than those
of various types of enclosed carbon arc lamps which were the
principal street illuminants in this country a few years ago.
Some advance has been made also in the design of lamp equip-
ments, notable among which are the prismatic refractor and a
variety of light density translucent glassware which combines
fairly good diffusion with high transmission. These improve-
ments in the materials of street illumination combined with the
increased sums which municipalities are appropriating make
possible a very general improvement in street lighting.
Skill in Application. — Recently installed systems are almost
invariably superior to the systems which they replace. Usually
the improvement is due in part to greater skill on the part of
the engineers in charge. City engineers, central station engineers
and manufacturers are better acquainted with the problems and
have acquired more skill in meeting them. The result is street
illumination of greater effectiveness. Notwithstanding this ad-
vance there are but few principles of street illumination which
are regarded as thoroughly established. Although the subject
has received perhaps more than a fair share of discussion and
study, it is still enveloped in much uncertainty. In the literature
and in practise there is much which indicates differences of
opinion in regard to principles of fundamental importance. It
must be admitted that progress in the conception of correct prin-
ciples is slow. Yet there is progress and it may be that by the
time most street lighting is made good, those of us who talk and
write of the principles may reach an agreement as to what con-
stitutes good street lighting.
It is the purpose of this paper to discuss the variables of street
illumination and the principles underlying the best use of modern
illuminants and accessories under modern conditions in this
country. Therefore, matters pertaining more especially to the
third factor entering into improvement in street illumination, as
enumerated in the opening paragraph1, will be discussed first.
1 This paper may be regarded as a continuation of the discussion presented by the
author before the 1910 convention of the Illuminating Engineering Society under the
title " Some Neglected Considerations Pertaining to Street Illumination ". Trans. I. E.
S. Vol. v, p. 653.
MILLAR: THE EFFECTIVE ILLUMINATION OF STREETS IO4I
CLASSIFICATION OF STREETS.
For the purposes of this discussion the following classification
of streets is adopted:
Class Description
la Metropolitan thoroughfares of greatest distinction,
it Important city streets largely traveled at night.
2a Business streets not largely traversed at night.
2b City residential streets.
3a Suburban residental streets.
3b Suburban thoroughfares.
It will be apparent that requirements for street illumination
are diverse as among these different classes of streets. For
example, the ia class of streets is distinguished by a requirement
for dignified, pleasing fixtures and for lamps and illumination
which should be of fairly high intensity, lighting building fronts
as well as street. Streets of the lb class are likely to be char-
acterized by much show-window and sign lighting which
augments the street illumination during the hours of greatest
traffic. Here intensities are likely to be highest, and the ordinary
fundamental requirements of street lighting are supplemented
by the desirability for recognizing acquaintances in the passing
throng and for detailed vision, approaching that common to in-
teriors at night.
In streets of the 2a class a moderate intensity of illumination
which lights building fronts as well as street is customary.
Policing purposes and good seeing conditions for the occasional
pedestrian are the principal desiderata. In streets of the 2b
class it is usually desirable to keep the light upon the street sur-
face, avoiding brilliant illumination of the upper stories of resi-
dence fronts and providing fairly good lighting for the low den-
sity vehicular and pedestrian traffic.
In streets of the 3a class it is likewise desirable to keep the
light upon the street, illuminating the sidewalks well to serve the
purposes of pedestrians. In streets of the 3b class, which are
the important automobile highways connecting populous centers,
the principal requirement is that of the automobile driver. Here
the most difficult problems of street illumination are encountered.
The discussion in this paper is applicable in varying degree to
streets of these six classes.
1042 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
OBJECTS OF STREET ILLUMINATION.
From several points of view the objects of street illumination
may be stated in somewhat different ways. The point of view
of the motorist differs from that of the pedestrian, which in turn
differs from that of the police commissioner and from that of
the merchant. When, however, one assembles the considerations
growing out of all these viewpoints, those of first importance
appear to fall within the comprehensive classification presented
by the National Electric Light Association Street Lighting Com-
mittee in 1914 which is as follows:
Fundamental Purposes to be Served by Street Illumination.
1. Discernment of large objects in the street and on the sidewalk.
2. Discernment of surface irregularities in the street and on the side-
walk.
3. Good general appearance of the lighted street.
It would appear that in proportion as these three purposes are
served the street illumination will be regarded as satisfactory,
and it may be concluded that no street lighting installation which
serves these three purposes reasonably well can be regarded as
unsatisfactory. The weight to be given each will vary in dif-
ferent streets though in a general way it is probable that the pur-
poses are served in the order named. It is possible to install at
a low cost a system which will reveal large objects (Purpose No.
1 ) while failing to serve the two other purposes. With increased
appropriations or more efficient illuminants, large objects may be
revealed to better advantage and surface irregularities (Purpose
No. 2) may also be revealed although the third object may not
be served. With still larger appropriations and still more ef-
ficient illuminants, discernment may be improved and a pleasing
appearance for the street (Purpose No. 3) by day as well as by
night may be had. All three objects may be served when appro-
priations are adequate.
Process of Seeing. — In streets at night objects are seen by
reason of contour, relief, shadow or color.
One perceives the contour of objects when they are markedly
different in brightness from their background. Since most large
objects on the street at night are darker than their background
they are usually perceived as silhouettes.
MILLAR: THE EFFECTIVE ILLUMINATION OF STREETS IO43
Contrasts in relief are perceived when the exposed surface of
an adequately illuminated object presents areas of different re-
flecting powers, or elements which are more or less favorably
inclined with respect to incident light, or elements which lie in
the shadow of other elements of the surface.
Small objects may be perceived by reason of their shadows
occasioned by the interception of sharply inclined rays of light.
Shadows of large objects are not always of value in promoting
discernment and are often misleading, as in case of the shadow
of a telegraph pole thrown across the sidewalk.
Color contrasts are not usually relied upon since in installa-
tions where discernment is at all difficult, color is usually lost and
objects are perceived more readily by other means.
The several kinds of contrast perception are suggested in the
accompanying series of photographs of test targets. These have
been located successively in six representative positions between
lamps in the street shown in Figs. 8 and 9. Fig. ia shows the
lighting effects by the centrally mounted lamps shown in Fig. 8.
Fig. ib corresponds with Fig. 9. The targets are of substantially
the same color as the street surface. It is to be noted that those
which are most clearly revealed receive the least light and are
silhouetted against their background. Those least distinctly re-
vealed receive on the observed surfaces about the same light as
their background.
Contrast perception is the ruling visual process with which
street illumination is concerned. To increase contrasts on sur-
faces to be seen is to better conditions for vision, a consideration
often ignored.
In much of the literature of street illumination, curves of
illumination intensity form the principal basis of judgment as
to effectiveness. There is a tendency to over-emphasize the im-
portance of incident light to the prejudice of other important
considerations. Three of the principal considerations which are
not emphasized directly by study of illumination intensity curves
are presented in the following paragraphs.
Silhouette Effect.2— When the writer directed attention to the
* Millar, Preston S., An Unrecognized Aspect of Street Illumination; Trans. I. E. S.,
vol. V (1910), page 456.
1044 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
silhouette effect in 1910, there existed but little appreciation of
its importance. During the five years which have intervened
there has gradually developed a greater appreciation of the ex-
tent to which it enters into conditions of visibility in street illum-
ination. Yet its very general applicability even now is un-
recognized by some engineers. There is an impression that only
in lighting of very low intensity is it the prevailing method of
discernment. As a matter of fact the silhouette effect is pro-
nounced whenever there are bright street or building back-
grounds. A photographic under-exposure of any street in the
daytime shows objects as silhouettes. The casual glance of an
automobile driver corresponds roughly with such an under-
exposure. The majority of observations of large objects on the
street in our more intensely lighted thoroughfares, especially in
the practise of automobile drivers, falls under this heading, be-
cause a driver is concerned primarily with avoiding obstacles and
usually looks carefully enough only to detect the presence of
pedestrians and other objects. Usually he sees these as dark ob-
jects silhouetted against the lighter street surface or building sur-
faces. The pedestrian too obtains distant views of large objects
as silhouettes, but as he moves more slowly and approaches ob-
jects more closely, he has opportunity for closer observation, and
in the more brightly lighted streets supplements discernment by
silhouette with actual observation of surfaces in relief.
Figs. 6a and 6b show illustrations made from the original sil-
houette photograph illustrating the importance of this effect in
street lighting.
Nature of Street Pavement. — Modern streets which require
greatest care in lighting are traversed by automobiles. The
majority of them are paved with asphalt, asphalt block, wooden
block, treated macadam, etc. As a result of automobile traffic
such pavements become oiled and polished. The high spots of
the pavement then reflect specularly. Fig. 4 is a night view of a
part of Columbus Circle, New York City. The pavement is of
wooden block. The street in the immediate foreground of the
picture is not traversed by vehicles. The pavement in the outer
ring of the circle, which appears in the middle of the photograph,
is traversed by vehicles and has become polished in the manner
icIH
Fig. ia.— Test targets in six representative locations as illuminated by centrally mounted
lamps as shown in Fig. 8. Illustrating reliance upon contrasts and different kinds of
contrasts presented to view.
Fig. ib.— Test targets in six representative locations as illuminated by lamps mounted as
shown in Fig. 9. Illustrating reliance upon contrasts and different kinds of contrasts
presented to view.
MILLAR: THE EFFECTIVE ILLUMINATION OF STREETS IO45
described. It reflects specularly and its brightness as viewed is
due largely to distant lamps.
Fig. 2 shows measurements of horizontal illumination intensity
and of brightness at the angle of an automobilist's view. The
broken line shows horizontal foot-candles as measured on East
80th Street, New York City. This has an ordinary asphalt pave-
ment and is illuminated by multiple enclosed arc lamps 365 ft.
(101.15 m.) apart. The continuous line shows brightness values.
0.6
. 0.000020 0.5
0
©•
£ 0.000016 «3 0.4
a. a
ec z
y 0.000012 $ 0.3
I 1
A
11
f 1
---- Horizontal Intensity
rEffective"Brightness
1 \
1 \
1 ^
a
z
<
a
0.000004 0.1
\
\
\
1
1
/
<
y
/
0.0
3 4
0 80 120 160 200 240 280 320 360 400
FEET
Fig. 2.— Curves of brightness and illumination intensity.
0.5
0 0.000016 0.4
o-
</>
0= ft
£ 0.000012 £ 0.3
1 ?
p 0.0OC0O8 £ 0.2
i 0.000004 0.1
— — — Horizontal Intensity
*Effective"Brightness
A
\
/
1
\
\
\
i
f
^N
/
/
f
\
\
\
^ >
:=^T
\ i
_^\
0.0
3 *
0 8
0 1
.'0 1(
FEET
>0 2(
» 2t
0 280
Fig. 3. — Curves of brightness and illumination intensity.
It will be noted that whereas the foot-candles vary in the ratio
of 46 to 1, the brightness varies in the ratio of 8 to i. This is a
street in which automobile traffic forms but a small part of the
total traffic.
Fig. 3 shows corresponding data for upper Seventh Avenue,
New York City, which is a street largely traversed by automo-
biles. The street is paved with block asphalt. The horizontal
IO46 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
foot-candles vary in the ratio of 10 to 1 ; the effective bright-
ness varies in the ratio of 2 to 1. The impression of uniformity
which one derives from a trip through the street is expressed by
this brightness ratio rather than by the foot-candles ratio. On
this street, which is of the boulevard, central parkway type, there
are three lines of lamps. The linear spacing of the lamps is about
125 ft. (38.1 m.). As the street is fairly level, a great number of
these lamps is within view at a given time. The street surface
consists largely of small polished areas which reflect specularly
In driving through the street one sees reflected in these small
polished areas imperfect images or part images of distant lamps.
Notwithstanding the rather wide spacing and marked non-
uniformity of illumination intensity, the effect is one of remark-
able uniformity of lighting. In driving one looks at the street
surface 200 ft. (60.56 m.) or more away, and the surface which
he sees is rendered bright by lamps which may be one quarter,
one half or even one mile away. Consequently the surface be-
tween lamps viewed from this angle is almost if not quite as
bright as is the surface near or directly under the lamps.
Any street which is largely traversed by automobiles, and
which has pavement of the types named above, is likely to ap-
pear rather dark because of the oil which is deposited upon it
from automobiles. It is, however, a most favorable surface for
street lighting purposes because of its tendency to reflect spec-
ularly. It was found that Seventh Avenue, New York City, de-
scribed above, has three to four times the effective brightness per
lumen of incident light of another prominent thoroughfare which
is paved with Belgium block.
Fig. 11, which will be referred to in another connection, is an
additional example of this effect as encountered in a country road
paved with treated macadam. Here lamps are spaced 500 to
900 ft. (152.4 to 274.37 m.) apart. The roadway between lamps,
from the driver's point of view, is well illuminated ; due in part
to its specular character.
Recognition of the fact that modern streets are likely to be
characterized by more or less of this specular quality necessitates
important alterations in some of the theories regarding street
MILLAR : THE EFFECTIVE ILLUMINATION OF STREETS IO47
lighting which have prevailed in the past and which are held at
the present time by some engineers.
Relation Between Lamps and Street Surface. — The effect of
glare in street illumination is dependent primarily upon:
1. The extremes of contrast within view; that is, contrast
in brightness between the light source and the illum-
inated surfaces.
2. The visual angle separating the glaring source from the
observed surfaces.
3. The portion of the field of view which is illuminated.
Glare militates against good street illumination, first in de-
creasing ability to see, and second, in rendering unpleasant the
appearance of the installation and the street. Insofar as it re-
duces visual power it manifests itself in three ways :
First, actual diminutions in ability to perceive small contrasts
in the presence of a bright light source. Second, distraction of
attention as a result of which small contrasts may not be per-
ceived when viewed casually. Third, a temporary dazzling ef-
fect which persists for a few moments after a bright light source
is viewed directly.
Figs. 6a and 6b illustrate the effect of glare. In Fig. 6b a black
spot covers the nearby light source. In Fig. 6a, the presence of the
light source distracts attention from the automobile and the view
is rendered less pleasant. In fact there is a little discomfort in-
volved in looking at the automobile. Nevertheless if one delib-
erately dispells the idea of the glaring source from his mind and
concentrates on the automobile, it can be seen in the picture just
as well as when the tab covers the light source. This picture
further illustrates the importance of securing adequate separa-
tion beween the light source and the observed object, the dis-
traction due to the light source being greater relatively when the
picture is held at a distance from the eye and the visual angle
between the source and object is decreased.
If a single brilliant light source, as a bare gas-filled tungsten
lamp is located over a dirt road in the country, the glare is very
bad. If the lamp is raised to a greater height or moved to one
side of the road, or if the lamp is enclosed in a diffusing globe,
14
IO48 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
the glare is lessened. If a number of additional lamps are strung
beyond it along the road, the glare is further reduced. If the
lamps, instead of being located over a dirt road, are located over
a treated macadam road, or better still, over an asphalt road, the
glare is less serious. Light colored buildings along the street also
assist in reducing the glare. In short, anything which reduces the
contrast between the light source and the road surface, or which
increases the illuminated area within view, or which separates the
bright light source from the road surface, reduces the effect of
glare.
Sweet in 19103 studied that part of the effect of glare which is
a measureable reduction in the ability to see, using a single light
source in a dark room. He found under these exaggerated con-
ditions that a large reduction in visual power could be traced to
the presence of a bright light source close to the center of the
field of vision. In 19144 working with others on the campus of
the University of Wisconsin, he pursued his researches, and has
given preliminary publication to some very interesting results.
In this latter research he employed from two to four lamps
mounted at various heights and with various spacing intervals
over a dirt road about 350 ft. (106.68 m.) long, with surroundings
of low light-reflecting power. It is not proposed at this time to
enter into a discussion of these tests, but it may be noted that
the only conclusions which they can indicate are those which
would apply to a short stretch of dirt road with surroundings of
low light-reflecting power. The modifications introduced by
street pavements of better reflecting qualities, by buildings along
the street, and by a greater length of illuminated street, have no
part in this research. This is a serious limitation, because the
effect of glare in street lighting is very largely reduced by each of
these three factors. The two researches make available informa-
tion which has its bearing upon street lighting principles. If,
however, the data are considered without due regard to the lim-
itations under which the tests were made, there is danger of form-
ing an exaggerated idea of the importance of adopting measures
which will reduce the effect of glare by decreasing the bright-
» An Analysis of Illumination Requirements in Street lighting, Journal of Franklin
Institute, 1910.
* Electrical Review and Western Electrician, March 6, 1915.
I 0^%
Fig. 4.— view in Columbus Circle, New York City. Note specular reflection from that
part of pavement which is traversed by automobiles; also absence of specular reflec-
tion from immediate foreground where there is no automobile traffic.
Fig. 5.— Sixteenth street, Washington, D. C, 100-cp. mazda lamps over curbs
and dark area in middle of street.
Fig. 6a. — For a demonstration of the importance of separating the glaring source from
the observed object hold the picture nearer to or further from the eyes, as the distance
from the picture to the eyes becomes greater the visual angle of separation becomes
less and the glare effect is magnified.
Fig. 6b. — Original street lighting silhouette picture. Illustrating importance of bright
street surface and showing how the automobile is discerned because the street surface
beyond it is bright, not because the light falling upon it renders it visible. For a
demonstration of glare see Fig. 6a.
I o 14 S"
Fig. 7. — Magnetite lamps in 2S-ineh globes as used in Washington, D. C.
4ft*
^p
1
s 1 —
1 ft <4^l lr
twiN'sH
■•-
-"•^ i.
Figs. 8 and 9. — Center versus curb mounting in same street.
'MjJSwst^' •i"'^v«^P» * 1
1
"■- i
.p^.''
%• s '
9 '*'* k3^SBBHS
H'-
l*Sk-:»~
4j
'
Fig. io. — View of country automobile road. I,amp wrongly located on inside of
curve. Glare obscures view of road beyond.
Fig. ii. — View of same road shown in Fig. io. I<amp on side of curve replaced by
lamp in the left of view. Change of location enables roadway to be seen. Note
specular reflection from roadway due to lamps 6oo and 1,000 feet away. Excellent
conditions for driving with large illuminants (Magnetite arc lamps with refractors),
widely spaced.
MILLAR : THE EFFECTIVE ILLUMINATION OF STREETS IO49
ness of light sources to low values. Since the problem is really
one of reducing contrast between the light source and the illum-
inated surfaces, the more constructive way of accomplishing the
desired end is to increase the brightness of the illuminated sur-
faces rather than to dim the light sources unduly. Excessive
brightness of light sources must of course be reduced. It is
common experience that a simple diffusing globe accomplishes
this reasonably well under most conditions. Too great reduction
in the brightness of the light source is unsatisfactory psychologi-
cally. We like a bright light source— we are dissatisfied with
illumination in which a bright light source is not visible. There-
fore the thing to do is to eliminate glare by increasing the bright-
ness of the street surface and where desirable that of surround-
ings, and by reducing the brightness of the light sources mod-
erately throughout the angles at which they are viewed.
With these considerations concerning the importance of the
silhouette effect, specular reflection from pavements and glare
well in mind, a discussion of the variables of street illumination
and of the several factors which the engineer must study in
planning a street lighting installation are next in order.
ILLUMINATION VARIABLES.
The effectiveness of street illumination depends upon the fol-
lowing :
(1) Intensity of light upon the street— there is no single
measure of intensity which serves all purposes. The average
horizontal intensity upon the street surface is most nearly satis-
factory. (2) Brightness of street surface— adopting automo-
bilist's viewpoint as to angle and direction. (3) Relation between
lamps and street surface — visual angle between the two and ex-
tremes of contrast encountered. (4) Contrasts produced on the
street surface and on objects on the street— this is largely a
function of the direction of the light. (5) Portion of total field
of view illuminated— this may be affected either by the number
of lighted lamps within view or by the area of surface which is
illuminated. (6) Appearance of installation and of street by
day and by night— lamps, fixtures, light distribution, etc.
IO5O TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
INSTALLATION FACTORS.
Each of the foregoing variables upon which street lighting ef-
fectiveness depends is affected by four or more principal instal-
lation factors. These are listed in the first column of Table I,
in which the variables are given as column headings. The pur-
pose in presenting this table is to emphasize the complexity of the
street illumination problem and to indicate the manner in which
the several elements are interconnected. Consider, for example,
street surface brightness as a variable in street illumination. The
table indicates that brightness depends upon the power of the
lighting units, the number of lighting units per mile, the kind of
lighting accessories employed, the location of lighting units, the
nature of the street pavement and the nature of the surroundings.
Alteration in any one of these conditions may influence the
brightness of the street and therefore the effectiveness of the
street illumination. An engineer who considers any one in-
stallation condition must appreciate that his decision may be far-
reaching in its influence upon the effectiveness of the lighting,
since every installation factor influences a number of these varia-
bles. Every street presents its own problems, and the utmost ef-
fectiveness of street illumination for a given expenditure is had
when each factor is applied with due regard to the relations set
forth in this table.
TABLE I.— Effectiveness of Street Illumination.
Variables
Influences through which factors operate
Relation Portion Appearance
between of field ofinstall-
Installation Intensity Bright- lamps of view ation and
factors which deter- of light ness and street Contrasts ilium- street, day
mine effectiveness on street of street surface** on street inated and night
Power of lighting
units * * * « *
Number of lighting
units per mile -• * * * *
Kind of accessor-
ies * * * * *
Kind of mount •• •
Location of light-
ing units * *
Nature of pave-
ment * * *
Nature of sur-
roundings * * *
** Visual angle and extent of contrast.
1 Visibility not ratio of reflection coefficients.
TABLE II-LIGHT PRODUCING EFFICIENCIES OF MODERN STREET ILLUMr
ASSOCIATION OF EDISON ILLUMINATING COMPANIES LAMP O TREF
(ARC LAMPS BUMMER 1914— MAZDA I.
tee arc 1 van-
00s makes of
:e and
metallic flame
(standard
I pc — ^ : lac
interred "or-
n omental "
i»ksvrii-tu>n OP lamp v\i> Bfll ii'Mi \r
Mr.AN Initial VAI.ueH
-> amp. a. c. compensator, clear globes, white (lame electroile .
; 10 amp. a. c. compensator, clear globes, white ilunic elect! ide
G. E. magnetite 4 amp., standard electrode, clear globe
G. E. magnetite 4 amp , high efficiency electrode, clear
G. E. magnetite 5 amp., standard electrode, clear glol>e
G. E. magnetite 5 amp., high efficiency electrode, clear globe- ■ ■
G. E. magnetite 6.6 amp., standard electrode, clear globe
G. E. magnetite 6.6 amp., high efficiency electrode, clear globe .
Westg. metallic flame 4 amp., standard electrode, clear globe
Westg. metallic flame 4 amp., high efficiency electrode, clear globe
loo-watt multiple
200 " "
3°o " "
400 " "
500 " "
7SO " "
1,000 " "
60-cp. 6.6 amp. series
100 " 6.6 " "
250 " 6.6 " "
400 " 6.6 " "
600-cp. 20-amp. series compensator
1,000 '* 20 " " '•
93
200
300
400
57S
938
1, 3°°
200
320
480
800
1,170
2.513
3.767
5,026
7.225
11,787
'6.335
574
1,005
2.513
4.021
6,031
10,053
100
200
300
400
500
75°
1,000
444
73
■83
300
32it
5<>4t
' I ,-. :
767
681
238
370
459
609
693
937
0.97
0.91
0.91
094
o.67J
o.63t
11. 7
125
12.5
125
14.4
'5-7
16.3
I3I
■3-8
134
18.8*
•9-9t
265
326
9.638
8,557
2,991
4.649
5.768
7.655
8,708
11,774
3.310
4,100
3'o
323
39o
371
5"
5"9
299
306
18.5
17.8
965
14.4
14.8
20.6
17.0
23- ■
1 1.1
'34
0.68
0.74
ittaper ;
audit v
s*>
la.
- :■
Curve P. or C
" B or C
" BorC
" BorC
•' BorC
" BorC
No material chan . - in cp. throagboat trial has keea aaaem
Curve D
" D
---
Dsnal fixture! and con-
tainers absorb from 7 to
35 per cent, of tin- light
given by the lamp.
F, GorH
F, GorH
F.GorH
F, GorH
F, GorH
F.GorH
F.GorH
F.GorH
F.GorH
F.GorH
F, G or H
84
180
270
360
5'8
S45
1,170
7S
196
3H
1,056
98
I
2.262
196
I
3.393
294
I
4.534
392
I
6.509
490
0
10.618
1
0
14.700
980
10.8
1-5
'-5
:
5-o
9S0
2.46.;
3.946
0.99
0.96
o-95
3-«
-
2.9
E, F.GorH
E.F.GorH
5.554
9.047
5 = I I
1 Total Inmens = scp / <v
1 laBif 11 (I,) = o.o5 acp., approx.
average eandlepom
Dpensator.
1 1 ril. t. '1 i.mying up to 20 per cent, of these values.
Flame arc lamp, clear globes
Curve H
Magiiiliir.-reflector and clear glolx
II LIGHT PRODUCING EFFICIENCIES OF MODERN STREET ILLUMINANTS
LXMINATING C
OMPANIES LAMP COMMITTEE DATA ON STREET ILLUMINANTS
MA/PA LAMPS WINTliR 19M)
,\M u:i I
■ Lmsrnva Sskvick
D s*
. POV sum i i l.uiii ] in., si u \ u i
709
580
7288
O.74
0-77
17.O
16.3
73%
79%
9-<S
14-4
J0.6
II. 1
57
Curve B or C
• B or C
" B or C
•• BorC
•• BorC
•' B or C
No material change in cp. throughout trim has been observed.
113
0.94
:-.r.i 00B-
■' the light
Curve E.F.GorH
• E.F.GorH
" E.F.GorH
" E.F.GorH
•• E.F.GorH
" E.F.GorH
" E.F.GorH
84
180
270
360
5>8
845
1,170
E.F.GorH
E.F.GorH
E.F.GorH
E.F.GorH
45-7
78
196
3M
E.F.GorH
E.F.GorH
1,056
2,262
3.393
4,524
6,509
10,618
14.700
2,463
3,946
5.554
9.°47
196
294
392
490
735
980
45-3
74-5
187
306
33'J
520$
099
0.96
0.95
0.97
o-75t
0.725:
10.8
II-5
n-5
13-3
12.7
13- 1
13-2
i6.8t
I7-4t
3655
130 lir. per trim
80 lir |>er trim
!.■ i«rmit
assign incnt.
317 lir. per trim
MANUI'AI TURK1
General Electric Co. approves assignment of values ; reports latest lamp with compensator consumes |
• type without compensator : scp. 890-total lumens 11190— watts 465— w.-r
lumens per w. 24.
Westinghouse Electric & Manufacturing Company reports for 1915 lamp electrode life of 130 hours ana. wit hoot coss-
inglier efficiency as follows: scp. initial 770— total lumens 9676; throughout life (average; scp. 640; total
lumens 8,041 terminal watts initial 445, average throughout life, 442; w.p.c. initial 0.58, throughout life 0.69; harness
per watt initial 21 7. throughout life, 18.2.
National Carbon Company reports for flame arc lamp as a type, 16.9 lumens per watt (w.p.c. 0.74) tnroogboot nfe.
with lamp equipped with light diffusing glass-ware.
Data insufficient to permit assignment. See manufacturer's statement.
G. B. Co. approves assignment of va
G. E. Co. approves assignment of val
r, B. Co. approves assignment of val
G. E. Co. approves assignment of va
G. E. Co. approves assignment of va
('.. 11. Co. approves assignment of va
lues. States electrode lives are for two sizes, respectively 230 and 350 hr.
lues. States electrode life is 180 hours.
hies. States electrode lives are for two sizes, respectively 150 and 225 br.
lues. States electrode lives are for two sizes, respectively 125 and 150 hr.
lues. States electrode life is no hours.
lues. States electrode life is 75 hours.
G. E. Co. states sliglulv higher candlepower and efficiency obtained in inverted " ornamental " type of lamp.
Westinghouse Elec. & Mfg. Co. approves assignment of values and claims 250 to 275 ho
Westinghouse Klec. & Mfg. Co. approves assignment of values
Approximate values for the Summer of 1915.
Initial watts per enudle Initial lumens per watt
0.96
0.88
0.82
O.82
O.82
O.76
0.71
0.9I
0.76
0.75
0.63?
o.6it
13"
14.3
15-3
15-3
15-3
16.5
17-7
12.6
13-8
•6.5
16.7
I9-9J
20.6J
Ap^ roximate average life under correct operating conditions
1,000 hours
1,000 "
1,000 "
1,000 "
1,000 "
1,000 "
1,000 "
Curve D
Metallic flame— reflector and clear globe
Curve E
Mazda with diffusing globe
Curre H
MAidn with diffusing jcloc*
MILLAR: THE EFFECTIVE ILLUMINATION OF STREETS IO5I
In attempting to discuss these several elements of the problem
it is necessary to generalize, and this in spite of the fact that the
great differences in streets of the several classes listed on another
page made generalization difficult. Nevertheless it is hoped
that a general discussion of the influence of each factor upon the
several variables will be of value, particularly since it is pro-
posed to note principally those features in which recent experi-
ence has suggested some new consideration.
She of Lighting Units and Spacing Intervals. — There is now a
general tendency toward the adoption of more powerful lamps of
one of the three types listed in Table II. These data are available
through the courtesy of the Lamp Committee of the Association
of Edison Illuminating Companies; in large measure they are
authoritative for lamps of the period stated and equipped as
indicated.
Of the above illuminants the flame arc lamp and the multiple
gas-filled tungsten lamp depreciate in candlepower 20 to 25 per
cent, throughout life. The magnetite lamp and the series gas-
filled lamps do not change materially throughout life.
Large versus Small Illuminants. — The cluster of lamps em-
ployed so largely in "ornamental or white way" lighting during
the past five years has yielded in favor in most recent installa-
tions to the single illuminant or less frequently to twin illumi-
nants on one post.
The effectiveness of the lighting, other things being equal, is
dependent upon the choice as between many small lighting units
and few large lighting units. In favor of the small illuminants
it is urged that greater uniformity results from their use; that
they may be mounted lower, thus avoiding shadows from trees,
etc. ; and it is added that when small illuminants are mounted
low, a larger percentage of their total flux is distributed over
the street surface. On the other hand, it is argued in favor of
large illuminants that they are relatively less costly per mile, and
that usually the appearance of a street lighted by them is more
pleasing.
There are two considerations not usually urged in this con-
nection. The first is discussed in more detail under the subject
of location of lighting units. Large illuminants are favored
IO52 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
from this viewpoint because they may be placed well out over
the middle of the street, where the specular reflection from street
surfaces allows the light to be applied in a more favorable direc-
tion than that from small illuminants which usually are mounted
low over the curb. Fig. 11 is an excellent illustration of the
advantageous use of large units in lighting a country road. The
lamps are placed 500 to 900 ft. (152.4 to 274.32 m.) apart and
18 to 25 ft. (5.48 to 7.60 m.) high. The effect is good for auto-
mobile driving purposes. An example of ineffective use of small
illuminants will occur to all who can visualize a wide, wet street
with lamps over both curbs. The lighting of the street surface
consists of a few bright streaks near the curbs, while the middle
of the street is dark. Fig. 5 illustrates this effect upon a dry
pavement. As modern street pavements are extended, and auto-
mobile traffic increases, the advantages of mounting lamps well
over the center of the street tend to increase, and the disadvan-
tages of small illuminants mounted low over the curbs tend to
become more apparent.
The second consideration was brought out prominently last
year by the Street Lighting Committees of the National Electric
Light Association and the Association of Edison Illuminating
Companies. It was shown that within reasonable limits, uni-
directional light is to be preferred to multi-directional light
because it enhances contrasts upon which discernment is depend-
ent. Objects and surface irregularities are seen more surely by
uni-directional light than by light coming from a number of
directions. From this it follows that, other things being equal,
the revealing power of a few large illuminants is greater than that
of many small illuminants, especially if the latter are staggered
along both curbs.
While these considerations do not clearly indicate the desira-
bility of large units, they do add weight to the arguments in their
favor.
LIGHTING ACCESSORIES.
Improved Distribution. — The most desirable distribution of
light depends largely on the nature of the street surface and on
the character of the street. Hence there is no such thing as a
correct distribution characteristic for all street lighting. The
Fig. 12.— Adjustable temporary installation employed in New York City to
determine best location for lamps.
Fig. 13.— Carlisle, Pa., 600-cp. mazda C lamps in prismatic refractor units.
Fig. 14.
-Fourteenth street, Washington, D. C, 100-cp. mazda C lamps about 10 feet above
curb and spaced at intervals of 80 feet along each curb.
Fig. 15.— Lake Avenue, Rochester, 500-
watt mazda C lamps, mounted 17 y2
feet above curb, spaced at average
intervals of 225 feet.
Fig. 16. — Main street, Rochester, 6.6-amp.
magnetite lamps. Located 14^ feet
above curb and spaced at 100 ft. in-
tervals along each curb.
MILLAR: THE EFFECTIVE ILLUMINATION OF STREETS IO53
prismatic refractor is successful in providing a distribution char-
acteristic which for a vertical plane conforms to the theoretical
requirements as laid down by some engineers. In other forms
it will doubtless provide different distributions as required. It
is an admirable device so far as re-direction of light is concerned.
However, it is objectionable in some forms because of excessive
brightness, due to its small size. Also when combined with the
casings with which it is usually employed, its appearance is not
attractive. Probably in the evolution of this useful device these
objections will be overcome.
The same considerations which underlie the design of the re-
fractor, namely the desire to increase the intensities on the street
surface at a distance from the lamps, would appear to favor the
adoption of asymmetrical horizontal distributions whereby light
which normally is delivered upon surfaces lying along the sides
of the street is directed upon the street surface. Lighting ac-
cessories to accomplish this purpose have been devised, but thus
far have not received the extensive trial which their theoretical
advantages would appear to warrant.
Diffusing Globes. — The employment of diffusing globes to
decrease brightness of light sources in the street has become more
general in recent years. Perhaps the extreme example in the
way of increased size of such globes is found in the Washington,
D. C, installation of ornamental magnetite lamps, in which 23-in.
(58.4 cm.) built-up alabaster globes of rather high density are
employed. (See Fig. 7.) As compared with the use of a clear
globe or of a lamp with no globe, a diffusing globe of fairly
large size is usually desirable because it improves the appearance
of the lighting unit, renders the appearance of the street more
pleasing and promotes good conditions of visibility.
It is desirable to secure the best possible balance between low
light absorption and good diffusion when selecting diffusing
globes. Test data on these two characteristics are of importance
and should not be neglected. Because of neglect of simple and
inexpensive tests of commercially available glassware, globes
are being installed which do not accomplish the purposes in view
so well as would other glassware. These either absorb a larger
percentage of light than is necessary to secure the desired degree
1054 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
of diffusion, or else diffuse less well than need be, considering
the amount of absorption.
Protection for the Byes. — At first glance it would appear that
street lighting purposes would be served admirably by a lighting
accessory which would concentrate a large proportion of the
light flux upon the street surface while directing but little light
at those angles which fall near the center of a field of vision in
a given installation. However, certain difficulties operate against
the success of such a scheme. With practicable mounting heights,
spacings have to be short if this is to be successful in illumin-
ating the entire length of the street. The general direction of the
light in such an installation is much more largely downward
than is usually the case. Wherever there are sufficiently short-
interval spacings to allow of such an installation, there usually
exists a requirement for lighting the building fronts. In such
installations the relatively high intensities on the street surface,
together with the large areas of considerable brightness which
present themselves to view, render the glare negligible when
ordinary diffusing globes are used. That is to say, in the only
installations where it is practicable to use such devices, their
eccentric distribution characteristics are unnecessary. Where
the surroundings are such that the lighting of building fronts is
undesirable or unnecessary, spacings are usually too great to
admit of the use of such devices, because their illuminating range
is too small. Also considerations of street surface characteristics,
discussed elsewhere, suggest that suppression of light at say 8o°
may do more harm by lessening the pavement brightness than can
be compensated by decreased brightness of source.
LOCATION OF LIGHTING UNITS.
Comprehended under this heading are such subjects as height,
transverse location and spacing. In most city installations these
aspects are standardized for a particular street. In lighting of
interurban roadways, lamps are sometimes located in accordance
with best judgment, varying considerably in all these particulars.
Location Transverse of Street. — As between center and curb
locations there is a considerable difference. In the first place
with lamps located over each curb, the street appears much wider,
as is illustrated by a comparison of Figs. 8 and 9 which are alter-
Fig. i7._ Federal street. Pittsburgh. Series a. c. flame arc lamps, white light carbons"
Lamps mounted 24 feet above curb and spaced at average intervals of 69 feet.
Fig. 18.— Fifth Avenue. New York, 400-watt mazda C lamps on twin posts mounted 19 feet
above curb and spaced at about 100 foot intervals along both curbs with extra lamps
at cross-street intersections.
Fig. 19. — Pennsylvania Avenue, Washington, D. C, 6.6-amp. magnetite lamps as illus-
trated in Fig. 7. Mounted 15 feet above curb, spaced at 50 It. intervals along both
curbs.
Fig. 20.— Fifth Avenue, Pittsburgh, 6.6-amp. magnetite lamps, mounted 18 feet above the
curb, spaced at approximately 80 ft. intervals along each curb.
MILLAR: THE EFFECTIVE ILLUMINATION OF STREETS IO55
nate test installations of the N. E. L. A. and A. E. I. C. Street
Lighting Committees.
In the lighting of important city streets this is usually a desir-
able condition. The lamps mounted over the curbs likewise illu-
minate the sidewalks and the fronts of buildings better. (See
Figs. 18 and 19.) When, however, the lighting of the roadway
becomes of first importance, as in streets of the 3b class, the best
use may be made of the light by locating the lamps as nearly as
practicable over the roadway so as to take full advantage of all
specular reflection from the street surface. (See Figs. 11 and 5.)
Height. — In regard to height of lamps there is also a wide
difference in requirements, depending upon the character of the
street. In some of the latest practice, powerful lamps are located
14 to 18 ft. (4.27 to 5.48 m.) over the curbs on business streets.
These, however, are backed by light colored buildings and the
entire surrounding is so brightly lighted that the glare is not bad.
With lamps over the middle of the street the background is
usually the dark sky, and usually there are not light colored
buildings to relieve the general darkness. Under these conditions
the opportunity for glare to become serious is considerable and
it is therefore necessary to locate the lamps rather high. The
improvement realized in increasing the height of lamps of mod-
erate power from 18 to 20 ft. (5.48 to 6.09 m.) is considerable,
while the improvement in increasing the height from say 27 to
30 ft. (8.22 to 9.14 m.) is not very great. The curve of glare
falls off rapidly with increasing separation when the separation
between the light source and the observed surface is only a few
degrees. Around a lamp which has a dark background there is
a zone of halation within which objects tend to become invisible.
Once outside this zone, the glare effect falls off less rapidly. It
is very important to mount the lamps high enough to insure that
the separation from the street surface is at least sufficient to
avoid this zone of serious glare.
Power of Unit as Related to Glare.— Other things being equal,
the objectionable effects of glare are greater when the lighting
units are more powerful. Hence it is approved practise to mount
the more powerful units higher than less powerful units.
Such a lack of separation is responsible for the serious glare
IO56 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
illustrated in Fig. 10. An arc lamp is located over the inside of
a curve in a road obscuring the roadway beyond. The angle of
separation between lamp and roadway is about 30. Fig. 11
shows the same road but with a lamp located over the outside of
the curve and separated from the distant roadway by about
200 when viewed as in driving. It must be recognized that
a bright light source obscures its immediate background. This
obscuration is greater if the light source is brighter or more
powerful, and is less if the background is brighter. In country
road or park drive lighting such obscuration is often very seri-
ous. The illustrations in Figs. 10 and 11 indicate one good way
of overcoming this difficulty. Recognizing the truth that under
such conditions the bright light sources will obscure a certain
region of the field of view, the source is so located that the back-
ground which it obscures is one which it is not important to see
and that the surface which it is desired to see is sufficiently
separated from the glaring light source to avoid difficulty.
Spacing. — All features of an installation should be treated in
such a way as to avoid dark areas between lamps, coupled with
low mountings for very bright and powerful lamps. To avoid
ineffective results due to multi-directional light which reduces
contrasts, spacings need to be greater when the lamps are stag-
gered along both curbs than when they form a line along one
side or over the middle of the street. The best spacing would
appear to be contingent upon the kind of pavement employed
and the nature of the surroundings. All the other factors should
be so handled that in driving one will not encounter the bad con-
dition of a bright light source preventing an adequate view of
the surface of the street beyond it.
Fig. 12 illustrates the very excellent practise which is some-
times followed in the City of New York, in locating lamps for
street lighting. Lamps which are temporarily installed may be
raised and lowered ; those mounted from the mast arm post may
be placed nearer to or farther from the curb, and those in the
center parkways may be moved about at will, the posts being
mounted in rock-ballasted barrels. A crew of men locate the
lamps in the trial installation as directed by the engineers in
charge and the locations which appear to give the best illumi-
MILLAR: THE EFFECTIVE ILLUMINATION OF STREETS IO57
nating effects are arrived at. Photometric tests are then made
to show the results obtained and to afford a basis for the plan-
ning of other installations.
THEORETICAL CONSIDERATIONS WHICH HAVE NOT BEEN
DEMONSTRATED.
Color. — In street illumination where intensities are low, it is
believed by some engineers that white light is more effective than
yellow light. According to this view, objects are revealed with
greater definition; smaller contrasts may be perceived, and there
is less suggestion of haziness in the atmosphere when white light
is employed. In accordance with the Purkinje effect there would
appear to be some basis for this theory, since it is well known
that in intensities of the order of o.oi foot-candle, we see almost
exclusively by red vision and the maximum of the ocular lumi-
nosity curve is removed toward the blue end of the spectrum.
Whether or not this effect is present in street lighting is one of
the interesting subjects of speculation at the present time.
Whether or not white light possesses advantage for low in-
tensity street lighting due to ocular peculiarities, it is certain
that it is preferred by many for high-class street lighting on the
ground that it is more suitable, pleasing and dignified than is
yellow light. This is perhaps a matter of color association, and
is surely a matter of taste. It, therefore, hardly finds place in a
discussion of this kind, and is merely mentioned in passing.
"Animation" of Light Source. — It has been suggested that the
slight fluctuation of light which characterizes arc lamps possesses
some advantage for street lighting purposes over the steady glow
of the incandescent lamp. So far as the writer knows, no dem-
onstrations have been undertaken, and it has not been shown
that this speculation has any basis in fact.
GENERAL STATUS OF THE PROBLEM OF STREET
ILLUMINATION.
There is an important consideration suggested in the first para-
graph of this paper. As more money is expended on street light-
ing and as more efficient lamps are made available, the intensities
of light in streets become greater. As the intensities increase, the
requirements for the best possible application of light to promote
IO58 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
good visibility conditions become less severe and the requirements
for application which improve the appearance of the street become
more urgent. From the standpoint of rendering visible the
street and objects upon it, the lighting of suburban automobile
roads where but little money is available for installation and
operation offers the best test for the engineer's skill. In first-
class streets we have already progressed to the point where
esthetics assume large importance. This does not mean, how-
ever, that the problems of street lighting are becoming less dif-
ficult; it means simply that the problems are becoming more in-
volved, and broader comprehension of the fundamental prin-
ciples of street illumination is becoming more essential.
Appendix. — In the appendix will be found some statistics of
very recent installations in streets of several classes showing
practise in this country as of the early part of 1915. These are
accompanied by a few photographs.
Acknowledgment. — The author wishes to express his indebt-
edness to a number of gentlemen who have kindly supplied some
of the photographs and statistics which are utilized in this paper,
and who are too numerous to permit of individual mention in
this connection.
DISCUSSION.
Mr. G. H. Stickney : There is more difference of opinion as
to what is the best practise in street lighting than in any other
class of lighting problems. This is due in part to the efforts to
classify a wide variety of demands into one or two groups of
practise, at the same time putting the extreme emphasis on the
cost. Since the disagreement originates with the ultimate light-
ing effects, the lack of agreement as to the methods of producing
such effects is not surprising.
The careful analysis presented in Mr. Millar's paper, while
not furnishing a solution of the problems, is an important aid
in that direction, through clearly denning some of the funda-
mental facts which have not been generally recognized.
One of the most important divergences in practise is that be-
tween the large and small, or the high power and low power
lighting units. There seems to be little doubt but that the larger
THE EFFECTIVE ILLUMINATION OF STREETS IO59
units are generally better for high intensity lighting, and the
smaller units more economical for low intensity lighting. The
majority of our street lighting problems, however, fall in a class
of intermediate intensities, where there is considerable question
as to which size of unit will give the best effect for the least cost.
Good lighting can be produced from either. The latest tendency
seems to be to follow the logical practise of applying units of
intermediate power. v
We often note the tendency to measure the value of street
lighting units in terms of their efficiencies. Although, all else
being equal, this would be a fair measure, practically, there are
other considerations, such as, maintenance cost, adaptability,
convenience, appearance, steadiness, etc., which often outweigh
a considerable difference in efficiency. This has been illustrated
in the transition from the open arc to the enclosed arc, and also
in the remarkable spread in the incandescent cluster light, which
despite its notorious inefficiency enjoyed an almost unprece-
dented popularity. This cluster lighting was never viewed with
high favor by engineers, and while it is now giving way to more
economical and artistic single light posts its former popularity
should be recorded as the vote of the public in favor of more
ornamental street lighting.
Referring again to the efficiency question, it must be remem-
bered that to-day the item of electric energy consumed repre-
sents only about 20 to 25 per cent, of the cost of street lighting
service, so that even large gains in efficiency represent relatively
small savings. Such gains can, therefore, usually be more profit-
ably taken up in raising the standard of lighting.
The practise of oiling the road and street surface has had a
very important relation to street lighting practise. Due to the
blackening of the surface, streets which were formerly quite sat-
isfactorily lighted become dull and dingy looking. While the
glint effect of such streets is valuable to the automobilist in dis-
cerning objects, the black surface absorbs so much light that it is
very difficult to produce a pleasing and cheerful lighting effect
and much more light is required than in the case of light colored
pavements such as asphalt. It can hardly be expected that the
color of pavements will always be selected to facilitate street
IO60 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
lighting, but there are many cases in which it would be desirable
to consider the street lighting in this connection.
Prof. Dugald C. Jackson: This paper is, I hope, a fore-
runner of other papers to be given at joint meetings of the two
societies which are here to-night. Papers of a similar nature
have been given by Mr. Millar and other authors before the
meetings of the Illuminating Engineering Society, but these
papers have not been given the general attention of electrical en-
gineers that the subject warrants.
There are certain features of this paper which impressed me
very much and of which I will speak. To begin, the paper refers
to the change of attitude of engineers who have to do with street
lighting, which has turned them from the enclosed series arc
lamp to other types of lamps, and for myself I want to express
very great satisfaction in that. I have always believed that the
enclosed series arc lamp (especially when operated on alternat-
ing current) was one of the mistakes of electrical engineers, and
that it arose by allowing the question of the cost of maintenance
of a particular machine or piece of apparatus to take the place of
consideration of the real effectiveness of its service. Fortu-
nately, electrical engineers and others are now turning their atten-
tion to more satisfactory illuminants, i. e., more satisfactory when
judged broadly, and not solely from the standpoint of how many
hours a particular lamp may be burned, or how much labor may
be requisite to maintain the structure.
On the other hand, I believe we are likely to be misled by the
charm of simplicity in the mazda lamp and perhaps go too far
in utilizing the slightly yellowish light for illuminating important
streets. Certainly in the great streets of our cities most in-
dividuals are more pleased with the white light than with the
yellowish light. There is no question about the possibility of
lighting streets and roads with mazda lamps of large candle-
power very satisfactorily, but a white light is to more of us more
satisfactory, more enspiriting, which is a feature of real import-
ance in a city street in the major business district. The yellowish
light, however, probably serves the purpose with full satisfaction
in the residence and also perhaps in less occupied business streets.
In my opinion, the question of large versus small units will
THE EFFECTIVE ILLUMINATION OF STREETS I06l
work itself out. I am convinced, that the large units are bound
to be used for the important streets of a city. The American
cities must, like the foreign cities, become convinced that they
need floods of illumination in the regions of great mercantile
activity, although they do not need so much light elsewhere. To
secure real flood illumination, large lamp units must be used.
There are few objects more graceful and beautiful than a pair
of fine white lights on a graceful post, when these lights are prop-
erly protected by a fairly lafge white diffusing globe — the globe
being large enough so that any spot in the tremendous amount of
light that may be given off may not have any serious effect on
the eye. On the other hand, there are cases where sincere effort
has been made to get rid of glare according to the mistaken ideas
of some man who put up the system, in which rows of large in-
tense lights, with diffusing globes, placed 22 or 24 ft. (6.70 or
7.31 m.) high, 150 to 250 ft. (45.72 or 76.20 m.) apart, down
miles of road make a nightmare to travelers on account of the
physiological effect of the continuous rows of illuminants on each
side, which affect the eye with great discomfort.
One of the most pleasing results of the recent work of illumina-
ting engineers in this country is the attention which is being
turned towards the use of graceful lamp posts in the cities. I
here avoid the use of the words "decorative posts," because the
phrase "decorative lighting" has covered such a multitude of
sins by way of ugliness during the last few years. Graceful posts
are coming into style. The old mounting of an arc lamp, or
some other lamp, on a strip of iron, fastened by a lag screw to
a crooked wooden pole, which otherwise carried crossarms and
wires, was a poor sort of expedient for supporting the street
lamps, but if our cities can recognize the worth of, and spend the
money necessary to secure graceful posts, I am sure that they
will be improved and made happier as places for living.
Mr. Walter R. Moulton : Referring to the discerning of
surface irregularities in streets, I have in mind one interesting
example in Baltimore where a water-front street about 100 ft.
wide is paved with Belgian block and is lighted by means of
luminous magnetite arcs on standards located on safety islands
down the center of the street. The rough spots in the street are
IO62 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
brought out very distinctly by the shadows cast and also by the
increased intensity of illumination on the face presented to the
source of light. Because of the nature of the paving, one would
hardly expect to find surface reflection, but objects do stand out
in silhouette as the granite blocks are worn quite smooth and there
seems to be reflection from each individual block. The condi-
tions of the street also illustrate very forcibly the advantage of
illuminants on one side of the roadway only as this condition is
quite analagous to such a road.
The effect of street paving on the illumination of a street was
very plainly shown when the paving on both Howard and Eutaw
Streets in Baltimore was changed from Belgian block to sheet
asphalt. The location of luminous arc lamps was not changed,
but after the completion of the asphalt paving the lighting condi-
tion of the street seemed to be greatly improved. Another in-
teresting effect of street surface is found on the Fallsway, which
is a new concrete structure. The entire surface of the road, the
sidewalks and a 3 ft. wall on either side are of concrete and
lighted by means of luminous magnetite arc lamps similar
to the downtown business streets. This roadway has been in
use about nine months and at the present time has absolutely no
specular reflection from its surface. The surface of the street,
however, seems very well illuminated and the diffuse reflection
from the light colored surface seems to replace specular reflection
very well in improving the apparent illumination of a street.
Specular reflection from the surface illumination is important
in other outdoor lighting than street illumination. There is a
large municipal bathing pool in Baltimore, covering over two
acres, which is used at night as well as in the daytime. A number
of incandescent lamp standards are located around the pool and
also on platforms and pedestals in the center of the pool itself.
The general illumination is very good, but ability to see objects
on the surface of the water is entirely due to the specular reflec-
tion of the lights on the surface.
The excessive brightness of a prismatic refractor unit combined
with a high candlepower lamp is forcibly illustrated by the diffi-
culty experienced in attempting to photograph such installations.
Would this not indicate that such units are brilliant enough to
THE EFFECTIVE ILLUMINATION OF STREETS 1063
interfere considerably with vision and would it not also seem
to point out that their size should be increased ?
The commercial value of lavish application of street lighting
in the downtown section is well illustrated in Baltimore where
over 1000 luminous magnetite are "white-way" lamps have been
installed. At night the business section of the city is made very
prominent, it shows up quite strongly from the hilly sections
surrounding the city and especially so from the bay. The illumi-
nation in the sky from a distance is quite strong and the tall
buildings stand out quite prominently against the sky as the en-
tire face of the building is illuminated.
This latter feature of lighting the building fronts is one that
should not be overlooked. The civic buildings, namely the Court
House, Post-office and City Hall are located on three consecutive
blocks with wide streets on either side and a plaza on each end
and between the buildings. There are several well designed
office buildings facing the civic buildings. The generous use of
white-way lamps in this section makes these buildings quite
prominent, especially as they are of light colored stone, the Court
House being of white marble. This section is made really more
attractive at night than it is in the daytime.
The esthetic effect of lighting standards or posts throughout
the city is quite important. If possible one typical design should
be carried out. In Baltimore a special design standard was de-
veloped for use with the luminous arc white-way lamps. This
same design has since been carried into the residence sections for
use with the incandescent lamps and round globes and it has also
been carried into the parks. There are a great number of bridges
in and around the city and this same design standard has been
scaled down and is to be found along the side wall of bridges.
Thus there is a harmonious effect produced that is very pleasing.
A contrast, however, has been made in Roland Park, an exclusive
suburban section, where a special design corner post has been de-
veloped, supporting a rustic lantern and also supporting name
plates for each street.
The beauty spots of a city can be made prominent and their
artistic value greatly enhanced by good street lighting. This is
especially true of the small squares and parks to be found in any
15
I064 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
large city. The bright street lighting surrounding the small
park serves as a background against which the dark foliage of the
trees shows up very strongly in silhouette. Often a dainty lace-
like effect is obtained. The lights in the small park itself serve
very well to bring out the beauty of well- formed trees or banks
of shrubbery. The variations of light and shade are such as to
make the park of untiring interest.
Mr. H. H. Magdsick: Mr. Millar has shown clearly what
factors determine the effectiveness of the illumination in streets
with characteristics typical of our main thoroughfares. For such
streets, where the requirements of the driver of a vehicle form
the major consideration, the importance of these factors can
scarcely be over emphasized. The discussion would not appear
to apply with equal force to most residence districts, which con-
tain a large proportion of the total mileage of streets we have to
light, where the safety and convenience of the pedestrian are
primary. In serving these the incident light is of far greater
importance than in the other class of streets and the silhouette
effect, specular reflection from street surface, etc., are of lesser
value. With the funds now available for street lighting in some
cities a sufficiently high intensity can be provided at all points
on the street to meet these requirements satisfactorily when
modern equipment is employed.
It is pointed out in the paper that a bright light source inter-
feres with vision most when the angle of separation between the
lisrht source and the surface viewed is small. This effect is to
some extent decreased by mounting the unit at a greater height ;
but considerations of cost, inefficiency and possible obstruction
of light, limit this method. It is not generally recognized that
much the same result can be secured by the use of prismatic
refractor equipment so installed as to direct the maximum candle-
power at an angle of, say, Jo° from the vertical, with a con-
siderably reduced intensity at the higher angles, which are viewed
when the angle of separation from the illuminated surface is
small. The use of this equipment likewise increases the bright-
ness of the street surface. A sufficient intensity is still emitted
at the higher angles to satisfy the desire for some brightness in
the illuminant and to aid vision when specularly reflected; how-
THE EFFECTIVE ILLUMINATION OF STREETS IO65
ever, it should be borne in mind that onlv certain classes of street
City and Street
Descriptio
Width of
roadway
in feet
Pittsburgh, Pa.
Fifth Avenue
Pittsburgh, Pa.
Federal .Street .
Chicago, Illinois
Dearborn Street
Rochester, N. Y.
Main Street . .
Hartford, Conn.
Main Street .
Washington. D. C.
Pennsylvania, Av
New York, N. Y.
Fifth Avenue.
(25 to 58 Sts.)
Corning, N. Y.
Market Street
Rochester. N. Y.
Lake Avenue
Milwaukee, Wis.
Grand Avenue
New York, N. Y.
Seventh Ave.
(no to 136 Sts.)
Chicago, Illinois
Troy Street . . .
Washington, D. C.
Sixteenth Street .
36
47
42
80
90 ft. bet
bldg. lines
109
92
36
Accessories
<oft.
(160 ft. bet
bldg. lines)
Bu Medium alabaster
I globes
BuA^ba globes
BuAlba globes
BuAlabaster globes
Kovulux, Form 1.
Alfe-inch segmented
Alabaster globe
— dense upper, me-
dium lower hemi-
sphere
BuLight Carrara globes
BuC
R. I. globe and
translucent glass
reflectors
Re Alabaster globes
Light alabaster
Bv globes
A] Special
ventilated
unit — light Carrara
globe
R<Alba globes
Ra6-inch Alba globes
Building
fronts
lighted ?
Yes
Well
ngnt sources are still visible, although in many cases the intrin-
sic brilliancy is reduced by diffusing globes. Nevertheless, the
lamps are conspicuous, and I have yet to see a globe which does
I 6 t> 41
APPENDIX
:. Street
^Hftmrgh. Pa.
^^Btb Avenue
^^■■rgh.
^^hl Street
^^■go. Illinois
^^^Eborn Street
^^^K Street . .
^^^■rd. Conn.
f Main Street . .
Washington. D. C.
Pennsylvania, Av
^Vork. X. Y.
Tnne.
Corning. X. Y.
-ket Street
Ro -ester. N". Y.
Lake Avenue
■Uiraukee. Wis.
^^■and Avenue
Mew York. K. Y.
^Berenth Ave.
to 136 Sts.)
^■Ingo. Illinois
Description of Street
Width of
n adway
in feet
Kind of buildings
36
47
42
-.0
90 ft. bet
bldg. lines
109
Business structures
Business structures
Business structures
Business structures
All kinds
60 Business structures
Business structures
50
92
So
5fi
soft.
'160 ft. bet
bldg. lines).
Residences
Business structures
Apartment build-
ings
Residences
Residences
Installation
No. of
lighting units
50
90
Approx. 82
(twin lamp)
123
200 (2 per post)
56
79
246
Linear spacing
if feet
along one curb
Approx. 80
69
94
400
92
Height
in feet
18
24
25
14 ft. 6 in.
14
15
19
13 ft. 6 in.
17 ft. 6 in.
19 ft. 10 in.
10 ft. 3 in.
Location
Both curbs -opposite
Both curbs— staggered
Both curbs— staggered
Both curbs— o p p o s i t e,
main section-staggered
outside.
Both curbs— staggered
Both curbs— staggered
Both curbs— staggered
Both curbs— opposite
Both curbs — staggered
Both curbs— opposite
In center of block (on
center isle) On curb of
intersecting streets at
house line of cross street
intersection
East curb only
Both curbs — staggered
Kind of mount
Brackets on
trolley poles
Ornamental posts
Ornamental posts
Ornamental posts
Twin lamp orna-
mental posts
Ornamental posts
Twin lamp orna-
mental posts
Ornamental posts
Ornamental posts
Bracket on
trolley pole
Ornamental posts
Ornamental posts
Lamps
6.6-amp. d-c. ornamental
luminous arc
a-c. series flame arc white
electrodes
a-c. series flame arc lamps
6.6-amp. inverted magne
tite
600-cp. mazda C.
6.6-amp. inverted magne-
tite— stand, elect.
120-volt, 400-watt multiple
mazda C.
400-cp., 15-amp. mazda C.
1000-cp. mazda C.
4.0-amp. d-c. series orna-
mental luminous arc —
long life electrodes
120-volt, aoo-watt multi-
tiple mazda C.
600-cp. mazda C.
5.5-amp. series mazda C.
approx. 75 watts
Accessories
Medium alabaster
globes
Alba globes
Alba globes
Alabaster globes
Novulux, Form 1.
23-inch segmented
Alabaster globe
— dense upper, me-
dium lower hemi-
sphere
Light Carrara globes
C. R. I. globe and
translucent glass
reflectors
Alabaster globes
Light alabaster
globes
Special ventilated
unit — light Carrara
globe
Alba globes
ih-inch Alba globes
Building
lighted!
Yes
7a
Well
Yes
THE EFFECTIVE ILLUMINATION OF STREETS 1065
ever, it should be borne in mind that only certain classes of street
surfaces reflect specularly to any considerable extent. A study
of the streets in many large and small cities has shown that this
is a negligible factor in the illumination of a large proportion of
the total.
In Table II the average life of series mazda C lamps under
correct operating conditions is given as 1000 hours. It may be
noted that while the manufacturers have made guarantees on
this basis to cover a large range of street lighting circuits and
operating conditions, the actual performance in service as re-
ported in the technical press and at a convention of electrical
associations shows that the manufacturers' rated life of 1350 is
conservative.
Mr. W. H. Pratt : There is an observation which I have
made, and which has rather been thrust upon me in reference to
street lighting, which I would like to offer for what it is worth.
There is a strip of boulevard, some four or five miles long, over
which I frequently drive in the evening, and it is illuminated so
that it works satisfactorily, so far as the visibility of objects on
the road are concerned. The sources of illumination are mod-
erate sized units, spaced very regularly. I find that when some-
what tired, especially when driving over this road, there is a
very painful effect due apparently to the very regular passage of
sources of light before the eyes. I wonder if this might not be a
factor at times to be considered in determining whether large or
small units shall be used. The effect is very noticeable and some-
times is really extremely painful. I can easily understand how
under the circumstances a driver might be led to make serious
mistakes from that cause. It has a somewhat hypnotic effect,
definitely associated with the very regular passage at rather fre-
quent intervals of the light sources through the field of vision.
Dr. John B. Whitehead: We have been shown in very con-
vincing and beautiful fashion the importance of specular reflec-
tion and the value of a highly reflecting surface in streets and
roadways. I notice in all the pictures and in the model that the
light sources are still visible, although in many cases the intrin-
sic brilliancy is reduced by diffusing globes. Nevertheless, the
lamps are conspicuous, and I have yet to see a globe which does
1066 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
not in some measure give the disagreeable impressions generally
associated with glare. I remember also that when Mr. Millar
showed us a lantern slide in which an attempt was made to
illuminate a road with concealed sources, the slide indicated that
the result was an extremely poor one and not to be compared
with that which had been obtained by these methods which he
endorses. The question arises, as to whether the distribution
curves of various reflectors which conceal the source completely
have been studied in their relation to the angle of incidence of
the light upon the road surface. In other words, would it not
be possible to get a considerable amount of scattered reflection
at high angles of incidence?
Mr. Peter Junkersfeld : Most of our discussion this evening
has been on the illumination of streets, largely from the viewpoint
of the pedestrian on the street, or the people using automobiles on
the street, or the general illumination of the street. There is
one other party whose interest should be considered, and that is
the resident along the street, and particularly the resident whose
home is opposite some of these high candlepower lamps. I have
in mind an installation of 3,000 or 4,000, 600- candlepower type C
mazda lamps in Chicago, installed under the direction of Mr. Ray
Palmer. That system of lamps was installed on tubular iron
poles, using tubular iron poles also between the poles supporting
the arc lamps, and the lighting is very satisfactory from the stand-
point of street illumination. A great many complaints, however,
have arisen from residents on the street. These high candle-
power lamps shine into the second and third story windows,
particularly in the summer time, when people do not want their
shades down, but want them part way up, so that they can get
as much air as possible, and it is quite objectionable from their
standpoint. Many complaints have come in and in some places
the residences along the street have taken matters into their own
hands and painted the sides of the globes. It finally resulted in
the passage of an ordinance under which any resident along the
street may have a special shade put on the lamp by paying $2
per lamp and $1 per year in advance for the maintenance of the
shade. It probably is not sufficient to cover the cost, but serves
as a deterrent against unnecessary shading. The lamps are
mounted on poles, 25 ft. (7.62 m.) above the surface of the street.
THE EFFECTIVE ILLUMINATION OF STREETS I067
In other sections of the city where wires are put under ground
by common consent the small unit lamps on low poles, 10 or 12 ft.
(3.04 or 3.65 m.) high, have been installed, and that system, from
the point of view of the residents, is very much more satisfactory
and at the same time gives very good street illumination.
I would add a word to what Mr. Stickney said and possibly
also to what Prof. Jackson said, and that is, after all, this whole
matter of street lighting must be a matter of compromise. There
are many other things which are to be considered besides illumin-
ation. The staggering of lamps improves the illumination in
many cases. That means, however, considerable increase in cost
in installation, whether the wires are overhead or underground,
because the wires must cross back and forth across the street,
or else there will have to be two lines of poles. There are a
great many other factors of that kind that must be taken into
consideration in every individual system.
Mr. Allen T. Baldwin : In the author's paper, in the para-
graph entitled "Power of Lighting Units," reference is made to
the depreciation in candlepower of the flame arc and multiple
mazda lamps. A depreciation of 20 to 25 per cent, is claimed for
each unit mentioned. Insofar as the enclosed type of flame arc
lamp is concerned, we have found at our laboratories that 15 to
20 per cent, is the average depreciation when measured as the
part of the total light flux that is lost through absorption by
dirty glassware. For white flame carbons the lower value is
nearer the true average.
The light absorption arises from two causes: the etching of
the globe and the adherence to the globe of deposits from the
arc. The loss of light as the result of etching is the smaller loss
of the two. It will probably not exceed 5 to 10 per cent., and a
test recently completed on a globe that had been in service over
700 hours showed that it was capable of transmitting 96 per cent,
of the light transmitted by such globes. The test was made in
such a way that this loss was that known to be due to etching
alone. Studies have shown that the etching and deposits are
least in that part of the globe where it is desirable to have the
best light transmission. At the end of the trim life the loss at
8o° from the vertical is approximately 5 per cent., while at io°
from the vertical the loss approaches 40 per cent, or more.
1068 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
A comparison of the distribution curves of the lamp at the
beginning and end of the life will show that the distribution has
been changed in a beneficial way. The deposit in the bottom of
the globe acts as a reflecting surface and extends the values along
the horizontal at the expense of the light directly along the
vertical. These facts point out that the candlepower deprecia-
tion is best determined as the loss of total light flux rather than
that in any given direction. In reality the increase in efficiency
of the lamps gained by eliminating globe etching and deposit
would hardly be enough to warrant more than passing attention.
In connection with this subject it is interesting to note that it
seems to be an inherent tendency of white flame carbons to give
an increase in candlepower as they are consumed, but not to a
sufficient extent to counteract the losses just referred to.
Mr. L. D. Nordstrum : The point Mr. Jackson brought up in
regard to the difference in illumination which might come about
when different types of lamps were used, I have had brought to
my attention several times in the fact that we have two different
installations in Fort Wayne, practically a duplicate form of
installation outside of the light sources used. The old lighting
system used the usual type of single unit placed on street corners,
usually in the center of the street. Some two miles of the main
streets were changed over to what we called ornamental lighting.
The poles were placed on the curbs on each side of the street and
staggered. They carried a double crossarm with a lamp on each
end and a fifth lamp in the center of the pole with ioo-watt
mazda lamps in each globe. This had been installed about a
year, and then for about the same distance a new form of light-
ing was carried out, the same method of pole installation, and
poles about the same height, in which we used 4-ampere magnetite
lamps. I think that everybody is agreed that the magnetite
installation gives much better illumination. Something like seven
or eight months ago we had in the evening a very dense fog.
These two installations happen to be along the same street, so that
they could be compared, and in this dense fog the light from the
mazda lamps seemed to be entirely blotted out. One could see
the mazda lamps about a block away. Going down that portion
of the street having the magnetite installation one could see
THE EFFECTIVE ILLUMINATION OF STREETS 1069
the magnetite lamps strung out along the street a fairly good
distance away, for several blocks, at least ; whereas with the par-
tially yellow light from the mazda lamps the illumination was
not nearly so effective.
Mr. J. D. Mortimer "(By letter): Skill in the design and
application of equipment for the illumination of streets has not
progressed as rapidly as has the design of illumination for build-
ing interiors. Attention to this branch of engineering has been
spasmodic. With the many interests involved, the practical de-
sign of a system of street lighting requires many more comprom-
ises between scientific principles, politics and finances than usually
occur in other engineering undertakings. Where the relative
importance of the different factors measuring the effectiveness
of street illumination is still in dispute, it is not surprising that
every engineer possessed of a street lighting client, differs from all
other engineers. It is hoped that Mr. Millar's analysis will ma-
terially assist in reconciling the less important differences and
concentrate future discussion on the remaining few but important
factors.
Efficiency and size of lighting equipment, character of distribu-
tion of illumination, intensity, street surfaces, glare, spacing,
mounting height and appearance, are all of importance in the
design of a street lighting system. They all have some bearing
on the ideal scheme. No design can be said to be completed until
it is known what the annual costs of operation will be. Assum-
ing that the ideal plan can be laid down, the question arises, are
the improvements worth the cost? The increment cost of small
improvements in illumination should not exceed their value.
Value depends upon time, place and the state of public opinion.
There will be fashions in street lighting as there are in archi-
tecture, street cars, politics, and hats. Fashion alone will con-
demn as obsolete any system installed to-day long before it has
served its mechanically useful life. This fact has a bearing on
extent to which effective illuminating value may be created by
additional costs. The costs may be added for a period of several
years and the value rapidly depreciate after its novelty has worn
off. The financial factor in a subject as commercial as street
lighting, is yet one of the most important, and no study can be
IO7O TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
said to approach completeness that does not incorporate the
monetary aspects as an essential part.
Mr. F. C. Piatt (By letter): Mr. Millar calls attention to
three means by which street lighting can be improved, ( I ) larger
municipal appropriations; (2) more efficient lamps and access-
ories; (3) greater skill in application. To this list I would add a
fourth item which is extremely important, even more so than the
obtaining of more efficient lamps : this is to procure lamps and ac-
cessories having a lower first cost and lower cost of operation.
For the ordinary magnetite or carbon arc or large size type C
mazda lamp the cost of energy amounts to about 25 per cent, of
the total cost of service (including interest, depreciation, etc.^
while the fixed charges and operating expenses comprise the re-
maining 75 per cent. Hence it is evident that if a 10 per cent,
reduction in first cost and operating expense can be made, the
total cost will be lowered as much as by a 30 per cent, improve-
ment in efficiency.
The mazda series lamp has made rapid progress in spite of the
existence of the magnetite arc largely because the cost of the
lamp and reflector is much lower than the arc lamp. Also the
constant current transformer is much cheaper than the magnetite
rectifier.
In regard to the question of large versus small illuminants, it
may be of interest to see exactly what the effect is from a cost
standpoint if the size of the units is varied. The only system in
which the size of units can be practically varied is that using
mazda series lamps, as with the arc lamps the only variation is
from large to larger candlepower, no small units being available.
The most valid argument against wide spacing of lamps is the
practical necessity where blocks are short of locating a lamp at
least at every street intersection to serve as a marker as well
as to supply some illumination along every road traversed.
Crooked, and tree lined roads also call for closer spacing and
smaller units.
In Mr. Millar's paper considerable attention is given to the
question of lighting for motorists particularly on suburban roads.
I do not see that the motorist should be given much consideration
except to so place the street lamps as to avoid serious glare, and
to insure that road intersections are well marked. The headlights
THE EFFECTIVE ILLUMINATION OF STREETS IO7I
of a motor car are much better for showing road irregularities
than any lighting system could possibly be, due to the shadows
obtained from the lights close to the ground.
The principal object in lighting suburban roads to my mind is
to insure safety to the pedestrian or other traveler without light.
This also applies largely to the lighting of city streets, where the
more pleasing effect and better conditions for pedestrians secured
by curb lighting seem more important than the lack of specular
reflection which might aid the motorist.
Mr. Preston S. Millar (In reply) : Prof. Jackson has em-
phasized the possibilities of further intensive study and develop-
ment in the illumination field. His point appears to be well
taken. Those who have visited the Exposition at San Francisco
have derived a great deal of inspiration in this connection.
Replying to the question regarding the measurement of effec-
tive brightness, it should be stated that the measurements were
made about five years ago and were rather crude. After a few
trials, we determined the usual angle of an automobilist's view
of the street surface, arriving, if my recollection is correct, at 2°
as a typical angle. With a photometer we then measured the
brightness of arbitrarily selected patches of street surface at such
angle.
Due to the great increase in automobile traffic during these
past five years and to the more general adoption of modern
pavements, the departure of the brightness curve from the curve
of incident light is probably now greater than was found to be
typical five years ago.
Mr. Moulton has shown that the prismatic refractors employed
in Baltimore are so bright as to spoil the photographic effect
by reason of excessive halations. It would appear to be proper
to ask if these refractors are not also so bright as to spoil the
illuminating effect. In one of the views which he has shown
there is an illustration of the lighting of a public building by
magnetite lamps along the curb. It is to be observed that the
lower stories of the building were lighted nicely, but the upper
stories were not well lighted. If these lamps could be moved
across the street from the building, securing a greater distance
and a better angle of incident light, the general lighting of the
front of the building would probably be better.
IO/2 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Mr. Magdsick has dwelt upon the point of view of the pedes-
trian as opposed to that of the automobilist. I am not sure
that these viewpoints are essentially different. In the proposed
lighting of a Cleveland street which he has described, I think
we arrive at that class referred to in the paper in which esthetic
considerations are of first importance. In such problems most
of the questions discussed in the paper are of relatively less
importance because there is so much light available that appli-
cation to secure the best visibility is unnecessary.
Dr. Whitehead has suggested that it might be possible to
obtain the advantages which come with specular reflection from
street surface and still avoid all glare effect. I think he will
find that in cases where we have to take advantage of specular
reflection the spacings are so great that light must be allowed
to emanate from the lamp at such a high angle that it will pro-
duce some glare. When the spacing is so short that the glare
effect can be suppressed, there is so much light that ordinary
exposure of lamps in diffusing glassware does not produce much
glare. The work of Mr. A. J. Sweet may be consulted with
profit in this connection.
Mr. Junkersfeld's citation of objection on the part of residents
to light on the uoper stories of houses is mentioned in the paper
as well.
Mr. Baldwin implies that the depreciation during life shown
for flame arc lamps is a bit too high. We have received criticisms
from others that it is a trifle too low. If we may be permitted
to average these criticisms, we will conclude that the figures
shown in the paper are probably substantially typical.
Mr. Mortimer's discussion emphasizes the monetary aspects
of street lighting as fundamentally important. To this no ex-
ception can be taken. They are of transcending importance. He
states that the increment cost of small improvements in illumina-
tion should not exceed their value. "Value depends upon time,
place and state of public opinion." I like to think that it is ap-
praisal rather than value that depends upon time, place and state
of public opinion. For the value of an improvement it seems to
me is measured in the added effectiveness of the lighting. Again,
I like to think that it is the opinion of public representatives rather
THE EFFECTIVE ILLUMINATION OF STREETS IO/3
than public opinion which determines the appraisal. Discussions
of this kind should promote ultimate consensus regarding ef-
fectiveness and should hasten the time when appraisal of street
lighting values by public representatives and public utility repre-
sentatives will be in agreement.
Mr. Piatt deprecates the consideration given in the paper to the
requirements of automobilists, stating that headlights furnish the
best lighting for his purposes and that therefore street lighting in
suburban roads should be designed principally for the purposes of
pedestrians. Within the city limits of some large cities the em-
ployment of headlights is not permitted. It is preferable to avoid
the use of headlights in much traveled streets, and it is entirely
practicable to do so if the street lighting is reasonably effective.
Investigation has shown that large differences in the effectiveness
of street lighting do not interfere seriously with the progress or
safety of the pedestrian. They do affect the motorist seriously.
The motorist's requirements are most difficult to meet and as the
result of failing to meet them is likely to be very disastrous, the
lighting of suburban roads should be designed largely with his
requirements in view.
Mr. Charles F. Lacombe (By letter) : Mr. Millar's paper
takes up the factors necessary for the improvement of street
lighting, the first two of which have been long hoped for and
much discussed, while the third describes the variable factors
which, while known to those who have worked on the streets in
designing street lighting, have not been so carefully described and
analyzed before.
Municipal appropriations, of course, limit the extent and quan-
tity of illumination that can be obtained. As this item of a city's
expenditures increases with its growth and develops increased
business with load characteristics favorable to the producer, the
city is entitled to a fair share of the increased efficiency of the
light sources used without additional expense. A liberal policy
of this kind on the part of the contracting company, with reason-
able appropriations and a fair length of contract on the city's
part, would go far towards the improvement of street lighting in
the United States. If a city were shown what could be done in
increasing the illumination by the use of the recent highly efficient
lamps for about the same amount of energy, there is little doubt
1074 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
that a term contract could be obtained justifying the expense of
changed equipment and a considerable volume of increased busi-
ness would ultimately result from the extension of the improved
illumination so exhibited.
Speaking comparatively the more efficient lamps and accessories
have arrived. The improved flaming and luminous arc lamps and
the gas-filled tungsten lamp give the illuminating engineer light-
ing appliances of wide range that he has never had before in such
completeness. This is due to the adaptability of the present
lamps to all grades of illumination desired, largely resulting from
the divisibility of the series gas-filled and multiple vacuum tung-
sten lamps throughout the lower ranges of intensity. A few
years ago we had to work with only the indivisible arc lamp sup-
plemented by the inefficient carbon incandescent lamp; the
present range of resources in new and improved lighting units
should prove a great incentive to the spread of good illumination
on streets.
It is worth while to call attention to the availability of the 60,
80 and 100-candlepower series, gas-filled and vacuum multiple
lamps for street lighting on several classes listed by Mr. Millar.
My remarks on this are based on prices prevailing in New York
city recently. In these smaller sizes of the tungsten lamp, we
now have new units of an efficiency which can be economically
used to replace enclosed arc lamps or gas lamps on residence or
similar streets. Such lamps may be used to advantage on streets
of classes 2b and 3a and are also available in many cases for
classes 2a and 3b.
By choosing the proper sizes for a given height and spacing,
excellent results can be obtained. With a reasonable height, say
14 to 16 ft. (4.26 to 4.87 m.), using good sized, white, slightly
inclined reflectors and carefully arranging the reflector, lamp and
socket so that the light source is well up towards and in proper
focus with the reflector, glare can be diminished. This is partic-
ularly important in the use of gas-filled series lamps. Another
form of reflector can be used to keep the direct rays of the light
from the stoops or windows of houses. In fact the line of direct
illumination can be controlled as to height within reasonable
limits.
The use of two, three or four of these lamps within the old
THE EFFECTIVE ILLUMINATION OF STREETS 10/5
spacings for enclosed arc lamps can usually be accomplished at
a slightly less annual cost and improve the lighting without sac-
rificing the unidirectional effect which the tests made under Mr.
Millar's direction for the National Electric Light Association and
the Association of Edison Illuminating Companies have shown
to be quite important. When gas lamps can be replaced by series
gas-filled tungsten lamps on line and lamp poles, the annual cost
is decreased with a large gain in illumination. On city streets
with underground service several methods of installation can be
utilized either with new or old equipment which will give in-
creased illumination at a less annual cost per candle and at an
equal or slightly increased cost of installation, compared with the
cost of old equipment, depending on the economy of construction.
An installation of this kind as generally described, using over-
head construction, was made by the writer about a year ago and
afterward largely used in New York city. In this case ioo-can-
dlepower gas-filled lamps at a height of 14 ft. 6 in. (4.44 m.)
from the road and spaced 120 ft. (36.57 m.) apart using white
enameled reflectors (slightly inclined) gave in minimum foot-
candles, measured on a horizontal plane near the street surface,
0.0146; maximum 0.551 and average of about 0.071, over a street
and side walk 46 ft. (14.02 m.) wide. It proved very satisfactory
for a 3a street, much more so than series enclosed 6.6-ampere
carbon lamps and at a slightly smaller expense. The lamps in this
case were placed on one side of the street only. In other cases the
lamps were placed on both sides and staggered, the spacing being
from 85 to 150 ft. (25.90 to 45.72 m.) apart along the curb, and
very satisfactory results were obtained. The lamps were
mounted on line poles. Wherever these arrangements were
used on 2b and 3a streets they were preferred by the inhabitants
to enclosed carbon arc lamps. They also proved satisfactory on
many suburban boulevards or thoroughfares designated as 3b in
the paper under discussion, and over fifteen thousand of these
small lamps are now in use in New York.
Medium sized gas-filled lamps are available for all grades of
lb, 2a and 3b streets for all kinds of spacing and mounting
heights, which are usually found already fixed. These lamps
must be carefully selected as to intensity for spacing and height
and used with proper diffusing globes or prismatic reflectors as
IO76 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
may be needed in each case. In these grades of streets and
working into class ia streets, luminous flame arc lamps are avail-
able and even more effective than the largest sized gas-filled lamps.
The luminous arc lamps are particularly desirable when their full
illuminating efficiency can be utilized. These more powerful
lamps at considerable heights would also be used for the lighting
of great squares, plazas or irregular spaces at diagonal inter-
sections of important streets.
With this great range of light sources, admitting of many and
accurate gradations in the lighting of various streets, it would
seem that we might fairly begin to give an average and minimum
scale of the illumination required on streets where silhouette or
contrast lighting is not sufficient but where direct illumination,
more or less powerful, becomes necessary as on ia and ib streets,
particularly, and in some cases on 2a and 3b streets, where rapid
and frequent motor traffic exists. Such a standard would be
of great value for safety, as a gauge of responsibility in accident
cases, and as a standard to which engineers may work safely.
It would tend to so standardize the lighting of streets that there
need be less changing of equipment and less interference with a
properly designed lighting scheme by the idiosyncrasies of chang-
ing municipal administrations. A standard of this kind was de-
scribed by Dr. Bell in his Johns Hopkins lectures* at Baltimore,
and is seen abroad in the high minimum standards of important
streets set by English and German engineers.
Mr. Millar in his paper and Mr. Sweet in another, have given
valuable data and recommendations as to the avoidance of glare.
These must be carefully borne in mind with the newer forms of
lamps. In my experience, lamps of 100 scp. or under do not
give a sufficient quantity of light to avoid glare by diffusing globes
in commercial street lighting installations. In other words, the
amount of light absorbed is too great in comparison with the whole
to be economical. This is borne out by the results of careful tests
in New York city with both series and multiple lamps. This
should be borne in mind, particularly, with the gas-filled lamp with
its small light source of great intensity, and glare should be taken
care of by height, good sized white reflectors, and careful ad-
* Lectures on Illuminating Engineering, (1910).
THE EFFECTIVE ILLUMINATION OF STREETS IO77
justment of the position of the small light source and the re-
flector. The general practise in this country is to hang the lamps
too law, and Mr. Millar's observations on height seem to bear
this out. While the costs of higher iron ornamental posts for
city use would be more expensive, such an installation using bare
lamps with well designed good sized reflectors would be more
economical in watts per candle output. The element of cost in
this regard does not exist where lamps are suspended from or set
on the poles of overhead lines. In my opinion, improved results
would follow placing the newer types of lamps in such cases
higher than formerly and dispensing with diffusing globes. The
English and German practise follows this idea in both large and
small units and it must be said that glare is not offensive in those
installations which use bare lamps and reflectors, or with flame
lamps with slightly cloudy globes or refractors, placed at heights
of 24 to 30 ft. (7.31 to 9.14 m.). They thus obtain the utmost
effect of their light sources and direct the rays downward and
along the street, obtaining a high over-all efficiency. The same
result could be obtained in cities in this country where there may
be obtained the height necessary to avoid diffusing globes on
lamps of high power.
The kind of pavements and their condition as Mr. Millar points
out have a marked effect on the general appearance of a street
lighting installation. This is most marked between a wet and
dry pavement with the extreme contrast between the specular
and diffuse reflection. Motor vehicle traffic has affected street
lighting in many ways on account of the necessity of stronger
lighting due to increased rapidity of movement and among these,
its effect on pavements is very marked. It calls for a smooth
surface pavement which is usually dark in color but becomes
highly polished by traffic giving much specular reflection. Under
extreme conditions this would approach the effect of a wet as-
phalt pavement. Under reasonably dry conditions with the usual
amount of light colored dust always present, these pavements give
a mild specular reflection of almost diffuse irregularity with the
agreeable effect noted on Seventh Avenue, in New York. Under
extreme conditions, though, it becomes a difficult problem to
counteract the extreme darkening of the surface of a street or
road. An instance of this occurred in 191 3 in Central Park
IO78 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
where the former dust colored macadam roads were treated with
oil and greatly darkened. A 50 per cent, increase in the candle-
power of the incandescent lamps hardly offsets this effect. These
roads were of course without any added illumination from private
sources or from reflection from buildings.
Mr. Millar's emphasis on these variables in street lighting is
well founded and shows that they must be taken into account
seriously in street lighting work. The best way to study these
variables is by trial installations on the streets themselves.
Mr. C. E. Stephens (By letter) : The application of electrical
energy in the production of street illumination, to my mind, is
one of the most important subjects for consideration by scientific
associations. More than any other piece of electrical apparatus,
the street lamp is in the public eye. Its importance is not due to
the value of this character of load as a market for electrical
energy, but to the good or bad indirect effect on the electrical
industry, resulting from whether our street lighting installations
are good or bad.
Referring to possible improvements in street lighting, it seems
to me that greater improvements can be expected in the immediate
future, from a more scientific application of available light
sources, rather than from radical improvements in the efficiency
of available light sources. While the efficiency of light produc-
tion is extremely low, the energy cost is also relatively low when
compared with the capital charges for interest and depreciation on
the fixtures, transmission, etc., and other items of cost that must
be included. A further improvement in efficiency of the source
of light would have to be very great in order to materially reduce
the present cost of lighting. It is, therefore, a fitting time to
carefully analyze the application of the source and to secure the
most illumination possible from a given flux or volume of light.
Let us hope that such investigations as are at present being
carried on by the electrical industry can be continued, to the end
that a standard of street illumination will be set which will
secure ample visual discrimination, with comfort, and a mental
activity, necessary for safety ; and further that the time will soon
come when the doctors will agree.
Mr. G. N. Chamberlain (By letter) : As a brief resume
of the general conditions and limitations of street lighting and of
THE EFFECTIVE IEEUMINATION OF STREETS IO79
the particular problems before the street lighting engineer, this
paper is the best that has come to my attention. The author has
given a logical division of the subject; he has clearly outlined the
different classes of street lighting and called attention to the
various desiderata.
The difference in the nature of the street surfaces within the
last few years and its importance upon the question of street
lighting is very opportunely mentioned by Mr. Millar. The ex-
tensive adoption of such surfaces giving almost no diffusion,
but a high degree of specular reflection, has brought about very
different requirements and these must be met by the engineer if
satisfactory results are to be obtained. The relative importance
and effect of glare in street lighting is another most important
matter. As is often the case with subjects given a great deal of
prominence, it is possible I believe to over-estimate the effect of
glare. A street so lighted that no light source is visible and the
brightest visible part is the surface of the street near the lamp,
certainly brings in no glare troubles, but is not a pleasing ar-
rangement to the passerby. How far we should go in regard to
cutting down the intensity of the light source and removing it
from the line of vision is one of the problems that call for further
investigation.
The question of large versus small light sources, while un-
settled, is not as prominent as it was a few years ago, the gen-
eral tendency being, as Mr. Millar points out, decidedly toward
the larger units. The cluster arrangement of smaller units, so
much in evidence a few years ago, is being almost entirely super-
seded by the single lamp standard. This change has been brought
about by the introduction of the ornamental arc and the high
candlepower incandescent unit.
Under the heading "Theoretical Considerations which have
not been Demonstrated," Mr. Millar considers the subject of
color and "animation" of the light source as one of individual
taste and speculation. The engineers who have made the claims
referred to have had extensive opportunities for tests and ob-
servation and have given expression to the decided advantages
of color and animation of light sources. To the writer's knowl-
edge, these two factors have determined the final selection of the
lighting units supplied in several important installations.
16
IOSO TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
GAS STREET LIGHTING.*
BY F. R. HUTCHINSON.
Synopsis: The following paper outlines the progress in street light-
ing by gas. Various steps in the development of gas lighting are described
and illustrated.
It shall be my aim in, more or less briefly, covering this sub-
ject by illustration and description a few of the many styles of
gas street lighting standards and lamps that have been designed
and put in rather general use since the introduction of the old
flat gas lamp.
Some comparisons in candlepower are given in the following
paragraphs, but all are not mentioned as complete data were not
available at the time of preparing the paper.
Fig. i pictures the flat flame gas lamp. On a consumption of
6y2 cu. ft. of manufactured gas per hour, this lamp developed
a lower hemispherical candlepower of 27.
Fig. 2 shows type of incandescent mantle street lamp, best
known as the "boulevard lamp," most commonly used following
the introduction of the incandescent gas mantle. This style of
lamp is to-day still popular and there are more gas lamps of this
design now in use than any other kind in America. The boule-
vard lamp develops a lower hemispherical candlepower of 64
and consumes 3^2 cu. ft. of manufactured gas per hour. It is
a well known fact that considerably greater efficiency is obtained
with the mantle lamp than with the old flat flame burner. With
but little more than half the gas, about two and one-half times the
light is secured.
Unfortunately American municipalities, usually space lamps in
accordance with their appropriations, which are generally small,
* A paper read at a meeting of the section of the Illuminating Engineering Society,
May 7, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
HUTCHINSON I GAS STREET LIGHTING I08l
rather than as they should to get the best results. In America
gas street lamps are spaced from ioo to 200 ft. apart ; in Euro-
pean cities about 65 ft. apart, situated usually 100 ft. diagonally
apart measured from lamp to lamp.
When the inverted gas burner came into general use for indoor
illumination, its economy was so pronounced in comparison with
the upright burner that both manufacturers and municipalities
began looking into its application for street lighting.
One mantle of the inverted type does not look well in the boule-
vard lamp, so a burner was designed to suspend two mantles as
shown in Fig. 3. This burner consumes about 5^4 cu. ft. of
manufactured gas per hour and develops 182 mean lower hemis-
pherical candlepower.
Following the introduction of the inverted gas burner, and its
application in the "boulevard type lamp," experiments were made
and lamps designed of various mantle units and of somewhat
ornamental appearance. One of the first of such types is that
shown in Fig. 4.
The post or standard was known as the "Boulevard," bearing
the same name as the lamp illustrated in Figs. 2 and 3. On this
post was suspended a three mantle gas lamp with a reflector
shade. This lamp developed 400 candlepower (mean lower
hemispherical) on a consumption of 11 cu. ft. of manufactured
gas per hour.
A somewhat more ornamental post was next constructed which
suspended two, three-mantle gas lamps equipped with elaborate
globes and clear outer skirts as shown on Fig. 5.
The candlepower of these lamps was considerably lower than
that of the lamp shown in Fig. 4, as the lamp in the latter case was
fitted with a shade and equipped with a clear globe, while the
lamps shown in Fig. 5 were fitted with clear outer skirts and
alabaster globes. The gas consumption was the same.
Another style of standard and lamp is shown in Fig. 6. This
standard may be equipped with three or five lamps each con-
taining one or two mantles as desired. With all lamps lighted,
this standard equipped with two mantles to each lamp consumes
I082 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
22 cu. ft. of natural gas or about 2,7 cu. ft. of manufactured gas
per hour. The candlepower is not known but claimed to be 1,000
with all mantles lighted.
Fig. 1 1 is a night view of a street showing the lamps and stand-
ards illustrated in Fig. 6 lighted.
Fig. 7 illustrates a lamp which is used between street inter-
sections and Fig. 8 a standard for street intersections. (See
Figs. 12 and 13.)
The lighting unit in these lamps consists of a double inverted
fixture containing two mantles. On a manufactured gas con-
sumption of 6 cu. ft. per hour each lamp produces 150 candle-
power (mean lower hemispherical). With natural gas, consider-
ably higher efficiencies are obtained.
The "Sixth City," Cleveland, O., not wishing to be outdone by
any of its neighbors has, through its energetic and ingenious
lighting superintendent, designed and is now using for its east
side parks and boulevards ornamental lamps of the type shown in
Fig. 10.
All these lamps are at present equipped with an automatic
clock attachment that lights and extinguishes the main burners
from a pilot light that is constantly burning. Fig. 15 shows a
two-mantle burner equipped with a clock attachment fitted to
the supply pipe.
Each lamp consumes 4.7 cu. ft. of natural gas per hour and
develops about 135 candlepower.
Fig. 17 shows the construction of a recently designed automatic
pressure valve — not yet tried and proven in actual use — which
is intended to displace the automatic clock device now used for
lighting and extinguishing lamps. This valve, also shown fitted
to burner in Fig. 16, operates by increasing and decreasing the
gas pressure in mains supplying lamps on park boulevards. The
details of operation are indicated in Fig. 17. (Gas supply enters
valve through 12 at pressure of five ounces pressure and raises
diaphragm which in turn raises valve point 10 allowing gas to
enter passage way 2 to lamp. At this pressure pilot is supplied
with gas through 3. When pressure is reduced to one ounce,
pressure is not sufficient to raise diaphragm which seats valve
point 10 in seat between 1 and 2. Hinged trip 5 which might be
termed "low pilot valve" is released when pressure is reduced
tjmoi
-*
be -
O
toT>^-
Fig. ii. — Night view of an installation using equipment shown in Fig. 6.
Fig. 12.— Showing type of equipment for street intersections.
Fig. 13. — Gas lighting installation on Delaware Avenue, Buffalo, N. Y.
Fig. 14. — Gas lighting at Panama-Pacific Exposition.
I al.
Fig. 15. Fig. 16.
Automatic clock lighting attachment for gas lamps.
TUBE TO
PILOT
Fig. 17. — Diagram of automatic clock lighting attachment.
Fig. 18. — Gas illumination at the Panama -Pacific Exposition.
Fig. 19.— A three-mantle, high pressure gas lamp.
HUTCHINSON: GAS STREET LIGHTING I083
from five to one ounce, which permits gas at this low pressure to
flow through 4 to pilot, maintaining substantially the same flame
on pilot as with five ounce pressure, without permitting any gas to
flow to main burner. Description of parts and ports: 1 — area
or passageway for gas to main burner at five ounce pressure and
pilot burner at one ounce pressure ; 2 — continued port or passage-
way to main burner ; 3 — port or passageway to pilot for five ounce
pressure ; 4 — port or passageway to pilot for one ounce pressure ;
5 — hinged trip or low pilot valve; 6 — oiled leather diaphragm;
7 — spring attached to 10 to close low pressure pilot valve;
8 — brass stop to equalize tension of spring 7; 9 — balance weight
to close valve point with one ounce pressure; 10 — main valve;
11 — flash governing screw to release air from chamber above
diaphragm; 12 — gas passageway for service entering lamp post.)
GAS LIGHTING AT PANAMA-PACIFIC EXPOSITION.
Fig. 14 shows a close view of a post and lantern equipment
used at the Panama-Pacific International Exposition for the
lighting of the "Zone." These lamps are equipped with a mer-
cury valve for distant control. The posts are located 75 ft. (22.86
m.) apart. All gas supplied to the exposition grounds is conveyed
in the mains at 30 pounds pressure. A by-pass cock is installed in
the box seen at base of the post where there is also a governor to
reduce the pressure to that of a 5-in. (12.7 cm.) water column.
All gas lamps are screened by specially designed lanterns of vari-
ous types. These lanterns consist of a wooden frame covered
with canvas in either pink or orange color and at night the illum-
inating effect is very beautiful. All entrances and exits to the
exposition are gas lighted, the entrances by three and five-mantle
gas lamps, the exits by one-mantle lamps.
Fig. 18 shows a night view of the "Zone." (Note the different
shapes and designs of lanterns surrounding the gas lamps.)
In the State and Foreign Area of the exposition the street
lighting is done with high pressure gas lamps. Fig. 9 shows a
standard and lamp. These lamps are mounted on posts 18 ft.
high. Gas is delivered to lamp at 3 pounds pressure. The mean
lower hemispherical candlepower is 1,160; the consumption is
24.30 cu. ft. (0.68 cu. m.) manufactured gas per hour.
Before leaving the subject of high pressure, — Fig. 19 shows
I084 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
a foreign three-mantle high pressure gas lamp which develops
a candlepower of 4,000 on a natural gas consumption of 35 cu. ft.
(0.96 cu. m.) per hour. On a short life test made on this lamp
from March 4 to 16, 1915, during a burning period of 160
hours, but one mantle was replaced through breakage. No
globes or other parts were replaced. The gas (natural) deliv-
ered at this lamp was at the rate of 35 cu. ft. per hour at 2-lb.
Fig. 20.— Method of suspension for gas lamps on streets not having
overhead trolley wires.
(1.36 kg.) pressure. In street illumination abroad, this lamp is
located in the center of the street about 30 ft. (9.14 m.) from
the ground. Figs. 20 and 21 show the manner of suspending gas
lamps over the center of street and the lowering gear. The con-
struction shown in Fig. 20 is used where there are no overhead
trolley wires on streets not exceeding 80 ft. (24.38 m.) in width.
The arrangement shown in Fig. 21 is for street crossings having
overhead trolley wires. The lamp is moved to the side and then
HUTCHINSON : GAS STREET LIGHTING
I085
lowered. Flexible metal tubing is used from an ell at the top
over to the lamp.
There are many other styles of standards and lamps than those
illustrated in this paper, but I have tried to select examples of
most kinds in somewhat general use.
Fig. 21.— Method of suspending gas lamps on streets having overhead trolley wires.
The United States has been slow to adopt high pressure gas
street lighting and it will probably be many years before it be-
comes very generally used, but time here, as well as abroad, will
see it in much more common use than now. The excellent quality
of light, high candlepower and economy of operation will be
recognized, and when it is, our fellow electric members of the
Society will have to look out for their laurels.
I086 TRANSACTIONS OF IEEUMINATING ENGINEERING SOCIETY
SHEET GLASS IN LIGHTING.*
BY EDGAR H. BOSTOCK.
This subject can best be treated under two principal divisions,
namely: (i) factory operations in the production of sheet glass;
(2) variations that can be made in the glass.
This will give an understanding of what results can or cannot
be readily obtained, and perhaps some idea of the advantages and
limitations of sheet glass as applied to fixture manufacture.
FACTORY OPERATIONS.
The factory operations herein described are those employed in
a Kansas factory, where the low price of gas from the adjacent
gas fields is very favorable for the manufacturer. The gas is
supplied through a 10-in. main, this particular factory consuming
about 1,500,000 cu. ft. of gas per day.
Sheet glass is made in a tank furnace the inside dimensions of
which are usually 18 to 20 ft. in width, by 45 to 60 ft. in length.
Such a furnace when in full blast contains anywhere from 300
to 400 tons of molten glass.
The furnace contains two recesses — one through which the gas
passes and the other admitting the air. The gas and air come
together so as to burn across the furnace. There are two sets
of flues filled with checker work, one set of which carries off the
exhaust gases while the other heats the entering gas. The fur-
nace is arranged so that the fire can be reversed, and the heat
accumulated in the checkerwork from the exhaust gas, utilized in
heating the entering gas and air. By this means a much higher
temperature can be secured than if the fire were fed with cold
air and gas.
This furnace heats the glass from the top down, rather than
from the bottom up, and there are particular reasons for so
doing. The specific gravity of clay is less than that of molten
glass, so that to keep the bottom in the tank, it is necessary to heat
* A condensed statement of an illustrated talk given at a meeting of the New York
Section of the Illuminating Engineering Society, May 25, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
BOSTOCK : SHEET GLASS IN LIGHTING
I087
from the top. The bottom of the tank is heated hardly to red-
ness, and the denser glass remains at the bottom.
The molten glass flows off from the upper surface to the outlet
from which it is worked. A ring of clay floats on the glass in
Fig. 1.— Steps in blowing sheet glass.
front of the working holes, and serves to stop the flow of glass.
The glass is melted from a mixture of sand, limestone and ground
carbon with a certain proportion of old broken glass. The mix-
ture is inserted in the furnace by means of the long handled
Io88 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
shovel. To protect his face from the heat, the workman wears
what is called a face board, which is held in place by a plug
inserted between his teeth.
Fig. i shows the method of working the glass in blowing and
forming a sheet. The workman employs an iron pipe about
50 in. long, the end of which is heated to a slight redness so that
the glass will adhere to it. Glass may have to be gathered six
or seven times, depending upon the size of the article to be made
and the density of glass. When a sufficient quantity is gathered,
the workman blows down the pipe forming a bubble inside the
molten glass. This is formed by swinging and rotating, the pipe
being rested part of the time on an iron block or "lazy- jack."
In blowing, the workman takes advantage of the expansion of
heated air, at proper intervals holding his thumb over the end of
the pipe instead of blowing. As part of the glass bubble cools
and hardens it is reheated and the operation continued. Owing
to the mass of glass, the lower part of the bubble retains its heat
longest. The cylinder is formed by rolling the bubbles on an
iron table. When the proper shape is secured, the further end is
blown open the cylinder placed on an iron horse and the cap
removed.
The cylinder is then carried to another secondary or flattening
oven, cracked open lengthwise, opened and flattened out on a sheet
of very highly polished clay. The workmen are very expert and
the sheet so produced is usually approximately of the size desired.
In fact a workman gathering 16 lbs. will gather all day without
varying more than 2 or 3 oz. They will make sheets to cut 40
by 60 in. with little more than the necessary allowances, and the
cylinders will not vary more than 1 in. in circumference from
end to end. Considerable physical endurance is necessary for
the pipe weighs 12 to 15 lbs., and the glass bubble out at the end
may weigh 20 or 25 lbs.
In cracking the cylinder for removing the cap, a thread of hot
glass is laid on the cylinder long enough for local heating and
then the proper point is touched with cold metal, perhaps an
iron strip and the glass cracks along the heated thread.
In splitting open, the workman will take a rod of iron heated
at one end, with some carbon to prevent scratching, and work the
iron up and down the cylinder. With the cylinder at just the
bostock: sheet glass in lighting 1089
right heat, one extreme edge is touched with his wet thumb, which
starts a crack that follows the iron practically the full length of
the cylinder. The heat in the flattening furnace is just sufficient
to render the glass malleable, say about 5000 C. The flattened
glass passes to the annealing furnace, through which it is carried
on rollers.
Another kind of sheet glass is , manufactured by the casting
and rolling process. In this a "pot furnace" is used, in which
pots about 45 in. in diameter are filled with the glass mixture
and heated. When all are ready the workmen lift out the pots
and carry them to a casting table, pouring out the molten glass on
the table and rolling it out to the required thickness with heavy
rollers, one, two or three pots being used, depending upon the
size of the sheet required. This method is used for making large
sheets of plate glass. Such sheets are usually cast and rolled to
a thickness of Y\ in., and later ground and polished down to Y in.
When glass is manufactured in thick plates it is necessary to
anneal it very carefully, and therefore as soon as the plate has
been rolled, it is taken to an annealing oven. These ovens are
often 400 to 500 ft. in length, and a large plate may be kept in
such an oven from 7 to 10 days before it is thoroughly annealed.
When the sheet is annealed, it is polished by electrical machin-
ery, first with rough river sand and then successively with a finer
sand, emery and rouge. Curious to relate, after the finest me-
chanical polishing, it is necessary to re-polish portions of the plate
by hand.
All the plate glass which is manufactured is ground down from
YA to Ya in. in thickness, in order to remove any inequalities and
warping which may be present.
Figured rolled glass is made by a slightly different process.
In this a printing roller is used instead of a plain one. After the
glass is rolled by the smooth roller into a sheet the printing is
put on by rolling a figured roller over the plastic glass.
Another process which will be of interest, although not a
method of manufacturing glass plates, is the pressing of glass
into various shapes. In this the workman gathers a certain
amount of glass upon an iron rod and puts it into a mold; a
second workman watches the mold and when it is filled to the
IO9O TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
proper height he cuts the thread with a pair of sheers. A cap is
then placed on the mold and it is pushed under a plunger which
is forced down into the mold forming whatever article may be
necessary.
A new process which has recently come into existence is that
of making window glass by machine. It is more or less success-
ful depending upon whether one makes hand-blown glass or
machine-blown glass. In any event, the inventor of this has fol-
lowed very closely the hand-blown process. It takes an expert to
tell the difference between the machine and hand-blown glass to-
day.
These are some general processes which it is necessary to un-
derstand in order to comprehend some of the more complicated
methods which are in use for making the various glasses used by
illuminating engineers.
In making colored glass, or glass designed to shut out certain
light rays, there are some further processes which have to be
taken into consideration. One common process is that of manu-
facturing flashed glass, a clear glass coated with a film of colored
glass upon one side. To produce this, the workman when he
first starts to "gather" dips his pipe in a small pot of colored
glass of the color desired, for the first and possibly for the
second "gathering." He then carries his pipe to a pot of crystal
glass and "gathers" on top of the colored glass the necessary
amount of crystal glass to form the sheet or the article that he is
going to blow out. As he blows and forms the different articles
the skin of the colored glass remains on the interior of the cyl-
inder, and will be distended to whatever thickness of film he
wants according to the quantity of colored glass that he has
gathered. By this process blown glass of various color densities
can be manufactured according to the thickness of the film of
color that is used.
Silver reflector glass is manufactured in the same way as
sheet glass up to the point where the workman blows the ball of
glass. The workman then thrusts the ball into a clam shell mold
upon which has been machined a series of lines, all ending in a
common point at the bottom of the mold. He then blows his
glass into the ribs of the mold. Compressed air is sometimes
bostock: sheet glass in lighting 1091
used for this process. The ball is then taken back to the furnace,
reheated and swung out in the cylinder where the marks upon
the ball are followed in cutting the cylinder. The skill of the
workman is brought into play to keep the line in exactly a hori-
zontal direction.
Crackled glass is made by a variation of this process. The
workman proceeds as before until he has the ball blown when he
thrusts the bottom of it into a receptacle containing water. This
must be done very carefully for if the glass ball is immersed too
deep it will crack. After reheating it, the cracks are melted to-
gether except just upon the skin where they have broken through.
When the glass is swung out into the cylinder, the crackled marks
being swung out with the cylinder, the plate becomes crackled
glass.
Muffled glass is made by the same general process except that
the blowing process is continued until the cylinder is formed
when it is dropped in a two-piece mold which closes upon the
cylinder, the workman blowing the glass inside the mold. He
then produces upon the cylinder whatever marks may be cut in
the mold.
The necessity for annealing glass referred to before will be
understood when it is realized that a sheet of glass of any thick-
ness at all cools much faster upon the outer skin than it does
within. Of course, in very thin glass it is of very little importance
but in glass of any thickness at all, even of one millimeter, a
strain is caused by the quick cooling of the outer skin which is
sometimes very uneven. It is possible to have a glass that will
not stand even the extremes of temperature in our own climate
here because it is not well tempered, and this problem increases
with the thickness of the glass because of the internal stress set
up is much larger. As an illustration of this point, glass tears
are sometimes made by dropping extremely hot molten glass into
a bucket of cold water, the skin of the glass being chilled im-
mediately while the interior is clear red. These tears may be
laid upon the floor and hit with a sledge hammer without effect on
account of the extreme hardness of the outer skin, but if by
any chance the outside skin is scratched at any point it will ef-
fect the internal structure, the internal strains are so great that
IO92 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
the "tear" is immediately reduced to a powder. This is exactly
what happens when a glass ball or a heavy blown globe is not
properly annealed. It may stand extremely hard usage, but
when once the surface is scratched, the ball is broken on account
of the unequal stresses.
*The writer became interested in the subject of sheet glass
through the influence and kindness of some of the members of
this Society. At that time there was very little known about the
subject. Illuminating gas was first used extensively in the Soho
Works of Watt and Bolten in Birmingham, England, and just
three miles from the works of Watt and Bolten stands the
large glass works of Chance Brothers & Company. It is very
likely that the first sheet glass used in lighting was made to pro-
tect the gas jet burners used at the Watt and Bolten Works.
There was very little further use made of sheet glass in lighting
until the time of electric lighting, as the small gas flames used did
not require very much protection.
One of the first instances that the writer remembers of the use
of sheet glass with a definite view of improving lighting condi-
tions occurred in the equipment of the United Engineering Build-
ing. In the ceiling lighting of the auditorium on the second floor
Mr. C. E. Knox devised the first large installation of ceiling or
dome lighting. He did not know what glass to use, as those
available were very few, so the glass chosen for this installation
was a crystal ripple, sand blasted. It was the only thing available
of any diffusive power that he could place between the lamp and
the line of the ceiling. He desired to keep the lamp out of view
and attained it by grinding one surface of the glass. The diffi-
culty was that a cleaning problem was introduced which will
probably exist as long as the installation remains.
The next large installation that came to the writer's attention
was the lighting of the Soldiers' Memorial Building at Pitts-
burgh, by Mr. Bassett Jones. Mr. Jones went into this problem
very extensively and measured the absorption and refraction of
a number of the various glasses. It was the intention to produce
a warm glow rather than a cold white light and therefore a glass
* The remainder of this lecture was illustrated by means of a number of sheets of
glass illustrating the various points discussed by Mr. Bostock. As no illustrations are
available, these cannot be shown.
BOSTOCK : SHEET GLASS IN LIGHTING IO93
was chosen in which the color is not apparent, such a slight amount
of tint was included ; so that while the absorption is only 10 per
cent., the effect is that of warmth when the lamps are turned
on. Tungsten lamps were just coming into use when this installa-
tion was planned. Two types of glassware were used in this
installation in order to equalize the lighting. Certain conditions
in the ceiling made necessary a slightly deeper tint of glass to
increase the amount of amber light. This glass was molded so
skilfully by the glass manufacturer that there is an appearance of
uniformity over the whole surface. This difference is mentioned
in order to emphasize the mobility of glass. The glass mixer
is able to mix colors in order to reproduce any given intensity
and shade.
Ten or fifteen years ago there sprang up an era of mosaic dome
lighting and a good many domes, good, bad and indifferent were
made without any regard to the illuminating value of the glass
that was used in them. The glass makers, however, in making
glass for these domes discovered certain facts in glass making, and
when the demand came for a diffusing glass to be used in the
new indirect lighting they were able by making a mixture of opal
and flint glass to turn out the glass which is now known as the
"alabaster" type. This glass is made by mixing a given amount
of opal and flint glass upon the casting table and rolling the
mixture in the same way that plate glass is rolled. The glass
mixer is able to vary the absorption of this glass by varying the
quantities of the ingredients. If, for instance, a certain type of
indirect dish is to be made in which it is necessary to have 60
per cent, absorption, the glass manufacturer simply figures out
how much opal glass and how much flint glass will give him that
60 per cent, combined absorption and reflection. It is possible to
do almost anything with this type of glass ; second and third
colors may be added, the opal may be tinted, and the flint may
be tinted.
Some six or seven years ago the writer became interested in
trying to do away with the great problem caused by the surface
of acid etched glass. The particular installation that was
brought to my attention at that time was the installation of
lanterns around the then new Pennsylvania Terminal. These
1094 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
had been glazed with ground glass and the cleaner was apt to take
a greasy rag to clean the glassware. The glass of course was
soon streaked with all shades of grey and black and it would be
impossible to even venture a guess as to how much light ab-
sorption had been added to the original glass. The problem at
that time was to find a glass in which the same effects would be
obtained as with ground glass, and yet a glass which was as
readily cleanable as window glass.
The glass which was finally adopted is made by a process
which produces a glass plain on one side and flashed with any
required color on the other side. The glass in this installation is
flashed with opal and as it was made to duplicate ground glass,
it has about 30 per cent, absorption. It is possible, however, for
this glass to be produced with absorptions of from 20 to 60 per
cent. This glass can be cleaned just as easily and as readily as
window glass.
Some four years ago when Mr. D'Arcy Ryan was planning the
lighting of the Panama-Pacific Exposition Buildings, he was con-
fronted with the problem of illuminating the windows of build-
ings which were lit by flood lighting so as to eliminate reflecting
points of light. One of the first troubles he discovered was that
when the windows are set rather deep in the facade, the windows
appear as black spots due to the fact that light passes through
the window plate at 900 and therefore is not reflected. The
problem was to glaze the windows with a glass having the
same luminosity under flood lighting as the rest of the facade.
A new type of glass was produced through research work by
Mr. Jones called "Deflex" glass. This, he found, set up the
maximum amount of specular reflection, and is the one which
was adopted by Mr. Ryan for the exposition buildings. With
the modification of a wire content this was used for the dome at
Horticultural Hall where Mr. Ryan obtained such wonderful
effects.
Last year Mr. Edwards of the National Lamp Works pre-
sented at our 1914 convention a paper on the lighting of rooms
through translucent glass ceilings, in which he gave the results
of his tests of several different glasses. It is interesting to know
that Mr. Edwards was led into this work by the desire of the
bostock: sheet glass in lighting 1095
National Lamp Works to glaze the rooms of their own buildings
at Xela Park with a glass which would give a maximum diffusion
so that the points of light from lamps within the room could not
be observed from the outside. Mr. Edwards picked out a rolled
glass which is very beautiful in design and workmanship, and
which sets up very good diffusion, and is at the same time an
artistic glass. The glass has abotot 54 per cent, transmission
which, considering the fact that it is of such a definite pattern,
is a highly efficient glass. It became evident after the test con-
ducted by Mr. Edwards had been undertaken that a different
theory of light diffusion in sheet glass could be evolved. Crystal
glass is, of course, the ideal glass in use for such installations
because of its small absorption. In all tests which were made
wherever a glass whose deflective surfaces were cylindrical in
shape, it was found that a better diffusion was secured. As long
as a definite sharp angle was present a direct reflection was notice-
able from the angle of the glass without transmission, and there-
fore, maximum diffusion was secured by making all reflective
surfaces cylindrical in shape. A new glass was, therefore, de-
vised from this acquired data and the manufacturers are now
making a rolled glass which contains a series of small semi-
cylindrical projections. It was thought at first that it was not
possible to roll this glass making these semi-circular projections
touch each other, and a small flat plane was left between each pro-
jection so that it is not a perfect diffusive glass. It is the writer's
opinion, however, that the right theory is being applied to pro-
duce a perfect diffusing glass. This is the glass that was used
in the crow's nest in the "YVoolworth Tower and it is being glazed
under the direction of Mr. Madgsick. This is the last word
which we have in sheet glass for diffusion of light to-day.
One other application of sheet glass to illuminating engineering
has been evolved quite recently. It is a new method of sign
lighting built upon multiple reflection of light. Fig. 2 illus-
trates the sign made up and the principle upon which it depends.
The sign is lighted by means of a line lamp and the theory upon
which it is based is that if the incident angle of the entering light
remains within the reflective angle of the glass it has been thrown
on, the light will be reflected back and forth within the glass and
will not leave it. Now if this were a plain piece of glass it would
17
IO96 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
not be apparent to the eye that there was any light there at all
except at the edges where the light escaped. If now the surface
of the glass is abraded by any means at all there is set up a dif-
ferent angle of reflection at that point and so the light is visible
MJ1TI
Fig. 2. — Diagram of sign. A and D, wire of straight-filament lamp. B and C, path
of light rays confined within reflective surface of glass. E, face of glass in double
sign so metered as to bring path of light within refractive angle of glass.
F, abraded surface, where light becomes visible.
at the particular point where the angle changes. In the first ex-
periments merely the surface of the glass was abraded, but better
results are attained by cutting the glass deeply. These signs have
recently been put on the market.
FERREE AND RAND: EXPERIMENTS ON THE EYE IO97
SOME EXPERIMENTS ON THE EYE WITH INVERTED
REFLECTORS OF DIFFERENT DENSITIES *
BY C. E. FERREE AND G. RAND.
Synopsis: In previous papers read before this society by the present
writers, the gradation of surface brightness and its distribution in the
field of vision were shown to be important factors in the effect of lighting
conditions on the eye. In the work described in the present paper, grada-
tion of surface brightness is made the chief variable. Inverted reflectors
of six degrees of density are employed, and a correlation is made between
the illuminating effects obtained and the tendency to cause loss of power
to sustain clear seeing and to produce ocular discomfort.
INTRODUCTION.
This paper is the fourth in a series in which the effect of differ-
ent conditions of lighting on the eye is investigated. In the
first paper, two tests were described — one designed to be used as
a general test for detecting the comparative tendencies of different
lighting conditions to cause a loss in the eye's power to sustain
clear seeing for a period of work; the other for detecting the
tendency to produce ocular discomfort. In the second paper, the
application of the first of these tests to various lighting conditions
was begun. Two purposes were had in making this application :
(1) the studying and perfecting of the test itself for use in
lighting work, which it is obvious could not be done effectively
under one set or type of lighting conditions;1 and (2), the inves-
tigation of pertinent lighting effects, the results of which could be
made both to serve as a guide for further work, and to provide
cumulative data from which conclusions may be drawn as the con-
ditions and stage of advancement of the work may warrant.
This paper was divided into two sections. In the first the test
was applied to the determination of the effect on the eye of three
lighting installations, direct, semi-indirect and indirect, so se-
lected as to give wide differences in illuminating effects. In the
second section the effect of six variations in intensity for the
direct and semi-indirect installations was determined. In both
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, 1915.
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
IO98 TRANSACTIONS OF IEEUMINATING ENGINEERING SOCIETY
of these cases the tests were all made at one position in the room,
the point marked as the position of the observer in Fig. 1 of the
present paper. Obviously, however, the effect of an unfavorable
installation on the eye will vary with the position of the observer
in the room. In the third paper, therefore, the tests were re-
peated for these installations at four positions in the room : the
first with six reflectors in the field of view ; the second with four ;
the third with two, and the fourth with none. The following
features were also included : the work of the intensity series was
completed, i. e., six intensities of light were used with the indi-
rect reflectors ; a test was described for determining the effect on
the fixation muscles of the eye; and a series of miscellaneous
experiments was conducted pertaining to the hygienic employment
of the eye. In these experiments the following points were taken
up : the effect of varying the area, and conversely the intrinsic
brilliancy of the ceiling spots above the reflectors of the indirect
system of lighting used ; the effect of varying the angle at which
the light falls on the work in a given lighting situation ; the effect
of using an opaque eye-shade with dark and light linings with a
number of lighting installations; the effect on the efficiency of
the fixation muscles of three hours of work under each of these
installations ; the effect of motion pictures on the eye for different
distances of the observer from the projection screen; and a deter-
mination of the tendency of the different conditions of lighting
used in these experiments to produce ocular discomfort, and a
comparison of the tendency to produce discomfort and to cause
loss of efficiency.
Time cannot be taken here even for a brief statement of the
results obtained in these experiments. For the purpose of this
paper, it will be sufficient to say that gradation of surface bright-
ness and its distribution in the field of vision were shown to be
important factors in the effect on the eye. In the work to be
described in the present paper, gradation of surface brightness
has been made the chief variable. Inverted opal glass reflectors
of six degrees of density have been employed and a correlation
has been obtained between the illuminating effects produced and
their tendency to cause loss of efficiency and to produce ocular
discomfort. As the work progresses, an attempt will be made
FERREE AND RAND: EXPERIMENTS ON THE EYE IO99
not only to investigate this factor further in some of its more
important relations to lighting practise, but to take up in turn, so
far as is practicable, each of. the other factors mentioned in the
former papers.2
CONDITIONS TESTED.
An effort has been made to get a series of reflectors similar in
size and shape and differing only in density. It is our ultimate
purpose to use these reflectors both in accord with the principles
of direct and indirect lighting, and by employing additional trans-
lucent and opaque reflectors, differing if need be in size and
shape, to vary first one and then the other of the distribution
factors mentioned in the former papers. So far, however, we
have been able to use only six of the number of reflectors needed
to carry out this plan, and these in accord with the principle of
indirect lighting. They were all turned towards the ceiling and
were installed the same distance from it. So installed, as the
photometric measurements will show, the chief variables have
been the brightness of the reflectors and the ceiling spots above
the reflectors, — more especially, the brightness of the reflectors.
The reflectors used will be designated here by the numerals,
I, II, III, IV, V and VI ; and will be described in greater detail
in an appendix to the paper. They were all installed 30 in.
(0.76 m.) from the ceiling3 and were held by Plume and Atwood
semi-indirect holders attached to cords dropped from the eight
outlets shown in Fig. 1.
It has been our wish to conduct this investigation, as has been
the case in all our work on the distribution factors, with the
quality and intensity of the light made approximately the same.
Unfortunately, with the material available, the quality of the
light could not be made in all cases uniformly alike. Clear tung-
sten lamps were used as light sources with each installation, but
two of the reflectors, I and II, were not free from color. The
density of these reflectors had been secured in part, by giving
them a brownish tone. Just how much effect this would have,
if any, on the results of the tests we are not prepared at this time
to say. The fact should be borne in mind, however, in considering
the results obtained. It was decided to make the intensity of
light as nearly equal as possible at the test object and to give a
IIOO TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
supplementary specification of the lighting effects in the remainder
of the room.
At the test object the light was photometered in several direc-
tions. It was made approximately equal in the plane of the test
object and as nearly as possible equal in the other directions.
The specification of the lighting effects in the remainder of the
room was accomplished as follows, (i) A determination was
made of the average illumination of the room under each set of
reflectors. The room was laid out in 3 ft. (0.90 m.) squares and
Fig. 1.— Plan of test room.
illumination measurements were made at 66 of the intersections
of the sides of these squares. Readings were taken in a plane
122 cm. above the floor with the receiving test-plate of the illum-
inometer in the horizontal, the 45 ° and 900 positions, measuring
respectively, the vertical, the 450 and horizontal components of
illumination. The 122 cm. plane was chosen because that was the
height of the test object. (2) A determination was made of the
brightness of prominent objects in the room, such as the test
card, the reflectors, the reading page, the specular reflection from
FERREE AND RAND: EXPERIMENTS ON THE EYE HOT
surfaces, etc. The brightness measurements were made by means
of a Sharp-Millar photometer with the receiving test-plate re-
moved. The instrument was calibrated against a magnesium
oxide surface obtained by depositing the oxide from the burning
metal on a white card. By this method the reflecting surfaces
were used as detached test-plates. The readings were converted
into candlepower per square inch by the following formula:
brightness = foot-candles/V X 144. (3) Photographs were made
of the room for each set of reflectors employed. They will not all
be included in this paper, however, because too little difference
in illuminating effects is shown for the different reflectors to
warrant so extensive a use of the photographic method of speci-
fication.
The tests were conducted in a room 30.5 ft. (9.29 m.) long,
22.3 ft. (6.797 m.) wide, and 9.5 ft. (2.895 m0 mgli. In Fig. 1,
this room is shown drawn to scale : plan of room, north, south,
east and west elevations. In the plan of room are shown the 66
stations at which the illumination measurements were made ; and
the positions of the outlets for the lighting fixtures, A, B, C, D,
E, F, G and H. In the drawing, east elevation, the position of
the observer at which the tests were taken is represented.4 So
far in the work with these reflectors the tests have been made at
only one point in the room.
Table I gives the illumination measurements for each of the
66 stations represented in Fig. I. These measurements were
made with the receiving test-plate of the illuminometer in the
horizontal, the vertical and the 45 ° planes. Tables II and III
have been compiled to supplement Table I for the purpose of
making a comparative showing of the evenness of illumination at
the 122-cm. level given by the six sets of reflectors. Two cases
may be made of this : (1) a comparison may be made of a given
component from station to station; or (2) the difference between
the components may be compared. To facilitate these compari-
sons (a) the mean variation from the average of each of the
components has been computed; and (b) the difference in the
average of the three components has been determined. Results
for the first of these points are shown in Table II ; and for the
second in Table III.
II02 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
TABLE I.
Showing the illumination measurements in foot-candles for each of the
66 stations represented in Fig. i for the six types of reflectors used.
Division A.
Vertical, reflector type 450, reflector type
Station
I
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
3i
32
33
34
35
36
37
38
39
40
4i
Horizontal, reflector type
III
I
I.40
I.50
I.49
I.S5
2.40
2.20
2.6o
2.90
2.70
i-54
2.10
3-90
4- 5o
3.20
3.10
4-5o
3.80
2.60
3-3°
4.10
5.20
4.0
4.0
4.90
3-90
2.50
2.80
4.80
5-8o
4-5o
4-50
5.60
5.o
4.70
5.20
4-5o
4.60
4.90
4.10
2.60
2.0
11
1-35
1.2S
i-52
1.46
2.20
2.40
2.50
3.10
2.60
1.41
1.88
4-3°
4.90
34o
3.10
4.40
3.10
1.86
2.40
3- 7o
4.60
3-50
3-7°
4.90
4. 10
2.10
2.80
5-85
6.0
3.80
3-9°
5-30
3.60
3.80
4.90
4.10
4.0
5-4o
4.10
2.40
1.67
hi
1.30
1.20
1.27
1.47
2.0
2.10
2.30
2.90
2.50
1.32
1.78
3-7o
4-5o
3-50
3.20
43o
3.10
1.90
2.50
3-7o
4- 50
3-So
3 7o
4.70
4.20
1.78
2.40
4.70
6.20
4-5o
4.60
5.60
4-25
3.80
5-o
4-50
4.60
54o
4.0
2.0
1.62
o.55
0.58
0.50
0.52
0.50
o-54
o.57
1-25
1. 17
1.30
1. 16
1. 10
1.1
1.03
I.I5
i-34
1.42
1.42
1.42
1-52
1.86
2.10
1.80
1.99
2.0
1.72
o-53
o.55
0.46
0.40
0.41
0.40
0.46
0.87
1.0
1.30
1.0
1.06
1.20
0.91
05
35
11
15
33
10
54
64
61
54
90
68
0.50
0.49
0.48
0.42
0.50
043
045
o.93
0.94
1.22
0.94
1.20
0.97
o.95
1.20
1.25
i-37
1. 14
1.32
i-i5
1.42
1.60
1.48
1.66
1.80
1.50
2.10
2.30
1.65
1.62
2.50
2.20
1.50
2.40
2.70
3.10
2.50
2.60
3-o
2.40
34o
3.80
34o
3-30
4.0
3-3°
3-7o
4.40
3.60
3-7o
4.0
3.20
2.0
2.70
1.70
1.70
2.20
1.48
1. 10
1.60
2.20
2.90
2.20
2.30
2.70
2.30
3-o
4.0
2.70
2.50
3-7o
2.60
2.90
3-5o
2.80
3-o
3-8o
3.10
1.72
2.40
1.90
1.69
2.10
1.62
0.97
1.90
2.20
2.70
2.30
2.10
2.80
3-3o
3.20
4.0
3.10
3-o
34o
2.80
2.80
3.80
3-3o
3-5o
4.20
3.20
FERREE AND RAND: EXPERIMENTS ON THE EYE
1 103
TABLE L— |
Continued.)
Horizontal, reflector type
Vertical
I
, reflector type
II III
45°,
reflector type
Station
I
II
hi
I
II
in
42
3-9°
4.40
4.40
I.80
I.60
I.64
3-4°
3.20
34o
43
5-40
5-40
5.60
2.20
1.86
I.84
4.70
4.0
4.40
44
4.40
4.IO
3-7o
2.IO
1.76
I.50
4.0
3-40
3.20
45
4.IO
4-3°
4.20
2.IO
1. 71
1.68
3-8o
340
3-3o
46
5.20
5.60
5-7o
2.IO
1.60
1.68
4.60
4.IO
440
47
4-50
4.20
4-5o
I.76
H58
1.52
3.60
3-30
3-30
48
3-9°
3-70
3.80
2.0
1.94
1.76
3.60
3- 30
3-3o
49
4.90
4.80
5.10
2.30
2.10
2.0
3-90
4.20
3.80
50
4.10
3.60
4.0
2.30
2.0
2.10
3.80
3-5o
34o
5i
3-90
3-7°
3-9°
2.30
1.90
1.98
3- 70
3-30
3-5o
52
4.40
4-5o
4.60
2.30
i-95
2.0
4.10
3-70
3-9°
53
3.60
3-7o
3.80
2.0
1.58
1.80
3-3o
3.20
3.20
54
3.10
3-5o
3-4o
I.70
1.48
1.46
3.20
2.90
3.10
55
4.10
4-3°
4.10
2.30
1.70
1.80
4.20
3-8o
3-7o
56
3.60
3-o
3-30
2.IO
1.80
1.86
3-50
3.10
3.60
57
3.60
3-o
3.80
2.30
1.82
2.0
3-5o
3-o
3-7°
58
4.40
4.40
5 -40
2.IO
2.10
2.10
4.20
4.10
4.40
59
3-3o
3.60
3.60
I.63
1.85
1.66
3°
3.20
3.20
60
3-o
2.60
2.90
2.0
1.90
1.66
3-5o
3.10
3.20
61
3.10
2.90
3.20
2.50
2.0
2.0
3-9°
3.60
3-9°
62
2.60
2.60
2.50
2.20
2.10
1.92
3-5o
34o
3.20
63
2.50
2.50
2.10
2.20
2.15
2.60
3-40
34o
3.10
64
3.10
2.30
3°
2.40
2.0
2.10
4.0
3-3°
3.60
65
2.40
2.40
2.30
I.98
1.65
i-59
3.10
2.70
2.80
66
1.23
1.25
1.20
Averaj
re 3.61
3-45
3-49
I.65
1.44
i-43
3-3i
2.98
3-o5
Division B.
Horizontal, reflector type
Vertical
IV
, reflector type
V VI
45° 1
reflector type
Station
rv
V
VI
IV
V
VI
I
I.50
i-45
1-37
2
I.32
1.36
1.30
3
I.42
1.40
i-35
4
I.50
i-53
1.58
5
2.30
2.50
2.40
6
2.70
2.30
2.40
7
2.6o
2.60
2.50
8
3-40
3.60
3-30
9
2.80
2.80
2.80
10
1-55
1.48
1.56
11
2.00
1.94
2.00
12
4.20
4-30
4.10
O.65
0.51
o.53
2.6o
2.40
2.10
13
4.70
54o
4.90
0.59
O.58
0.60
2.90
3.IO
2.90
14
3.60
3-4°
3.60
O.56
0.49
0.50
1.88
1.88
1.92
II04 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
TABLE I.— {Continued.)
Horizontal, reflector type Vertical, reflector type
45°, reflector type
Station
IV
V
VI
IV
V
VI
IV
V
VI
15
3.10
3-4o
3-3o
0.58
0.49
0.43
1.72
1.80
1.80
16
4.40
4.70
4.80
o.55
0.40
0.56
2.30
2.70
2.60
17
3.10
3.60
3-7o
0.44
0.43
0.50
1.64
1.85
2.0
18
1.88
1.96
2.0
0.49
0.51
o-57
1. 14
I.I5
I.I5
19
2-75
2.60
2.80
1.25
1. 10
I-I3
2.10
1.88
1.84
20
4.20
3.80
4-30
1.20
1.20
1. 18
2.70
2.30
2.60
21
4.60
5-o
5.o
1.22
1.48
1.36
2.80
2.50
3.20
22
3-7°
3.80
4.10
1. 18
1.05
1.04
2.50
2.40
2.50
23
3.80
4.40
4.20
I.I5
1.26
1.06
2.30
2.70
2.50
24
5.20
5-9o
5-7o
1.47
1-52
1.27
3.20
3-3°
3-o
25
4.90
4-50
4-30
1-25
1.31
1.07
2.90
2.80
2.40
26
2.40
2.50
2.20
27
2.70
2.80
2-75
28
5-io
4.90
5.20
i-45
1.24
1. 14
3.80
34o
3.60
29
5.60
6.10
6.40
i-54
i-34
i-35
4-3°
4.40
4.60
30
4-3o
4-3°
4-5o
i-37
1.27
1.36
3.20
3-o
3-5°
31
4.20
4.0
4.40
1.30
1.26
1.30
3-o
2.90
3-3o
32
5.60
5-8o
6.20
1.38
1.40
i-53
3-7o
4-25
4-5
33
4.10
4-50
4.80
1.42
1.28
1.38
3.10
34o
3.80
34
4.0
4.0
4.20
1.80
2.0
1.88
3-o
3-30
3-5°
35
5-4o
5.60
5-8o
2.10
2.20
2.40
4.0
4.0
4.40
36
4.40
4-30
4-5o
1.70
2.0
1.98
3-4o
3-5o
3.60
37
4-3o
4.40
4-30
1.88
1.96
1.92
3-4o
3-30
3-5°
38
5.20
5.o
5-5o
2.30
2.30
2.20
4.60
4.10
4.40
39
4-3°
4.20
4-5o
2.20
1.68
1.90
3-8o
3-3o
3-7o
40
2.60
2.40
2.60
4i
1.80
1. 81
1.92
42
4-50
4.20
4.40
1.82
1.90
1.85
3-5o
3-6o
3.80
43
5-4o
5-5o
5-8o
2.10
2.10
2.10
4-5o
4-3o
4.80
44
3.80
3-7o
4-5o
1.90
2.10
2.0
3-3°
2.70
3-9°
45
4.20
4.40
4.60
1.90
1.90
1.98
3.60
3-9o
3-9°
46
5-4°
5-8o
6.20
1.90
1.85
1.88
4-30
4.70
4.60
47
3-90
4.0
4-50
1.80
1.78
1.72
3.60
3-3o
3- 80
48
3.60
3- 7o
4-5o
1.91
1.94
2.30
3.20
3-3o
4.0
49
5.o
4.90
5-30
2.20
2.60
2.60
4-5o
4.60
4.80
50
3-9°
4.0
4.20
2.40
2.20
2.80
3-7o
3-7o
4.20
5i
3-90
3-8o
4.20
2.40
2.20
2.60
3-7o
3.60
4.10
52
4-65
4.70
5-o
2.50
2.50
2.50
4.10
4.20
4.20
53
4.0
3-5°
4.0
2.10
2.10
2.10
3-5o
3.20
3.60
54
3-7o
3-5o
3.80
1.74
1.70
1.82
3.20
3-3o
3.60
55
4.20
4.70
5.o
2.40
2.0
2.20
4.0
4-3°
4.90
56
3.20
3-3°
3.60
2.20
2.20
2.10
3-5°
3.60
3-9o
57
3-4o
3-5o
3.60
2.20
2.30
2.20
3.60
3- 80
3-7°
58
4.60
5-io
5- 20
2.20
2.30
2.40
4.20
4.90
4.60
FERREE AND RAND: EXPERIMENTS ON THE EYE 1 105
TABLE I.— (Continued.)
Horizontal, reflector type Vertical, reflector type
45°, reflector type
Station
59
60
61
62
63
64
65
66
IV
3-9°
2.50
3.20
2.30
2.50
3.10
2.30
1. 14
v
3-9°
2.50
3.20
2.60
2.40
2.90
2.40
1. 16
VI
4-3°
3-o
3.80
2.50
2.60
3-o
2.40
1.42
IV
1.78
2.0
2.30
2.10
2.60
2.30
2.0
V
1.81
2.20
2.60
2.30
2f8o
2.40
2.0
VI
2.40
2.40
2.40
2.40
2.IO
2.40
2.IO
IV
3.20
3-30
4.40
3.20
3.60
4.0
3.10
V
3-50
3-70
4.20
3-o
3-8P
4.0
3.00
VI
4.0
3.80
4.6
3-4o
3-4o
4.0
3.10
Average 3.80 3.70 4.20
1.71
3-3° 3-3i 3-49
1.675 1.68
TABLE II.
Compiled from Table I to show a comparison of the evenness of the illu-
mination at the 122-cm. level given by the six types of reflector used
Mean variation of components
Percentage of
mean variation of components
Type of
reflector
Vertical
Horizontal
45°
I
O.976
O.516
O.582
II
O.999
O.487
O.576
III
I.066
O.430
O.562
IV
1. 21
O.498
O.60I
V
I. IO
0.539
O.628
VI
1.47
0.574
O.677
Vertical
Horizontal
45°
27.O
31-3
17.6
29.O
33-8
19-3
3°-5
30.1
18.4
31.8
29.7
18.2
29.8
32.1
I9.0
35-o
31.2
19.4
TABLE III.
Compiled from Table I to show the difference in the average values of the
three components of illumination for the six types of reflector used.
Difference between components
Percentage of
difference between components
Type of Vertical and Vertical
reflector horizontal and 450
I I.96 O.3O
II 2.0I O.47
III 2.06 O.44
IV 2.125 0.50
V 2.02 0.39
VI 2.49 0.71
450 and
horizontal
1.66
i-54
1.62
1.625
1.63
1.78
Vertical and
horizontal
54-3
58.3
59o
55-9
54-6
59-3
Vertical
and 450
8-3
13.6
12.6
13.2
10.5
16.9
450 and
horizontal
50.2
51-7
53-1
49.2
49.2
51.0
Figs. 2-5 are taken from the series of photographs showing the
illumination effects produced by the six types of reflector used.5
As was stated earlier in the paper, not so much use has been
made of the photographic method of specification in this as in
the former papers. In the former papers three photographs were
given for each set of reflectors. One of these was taken from
the south end of the room at a point 4 ft. (1.22 m.) from the
II06 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
west wall. This photograph was taken so as to comprehend as
much of the room as was possible in one view. It included the
greater part of the ceiling, floor, and north wall, six of the fixtures
and about one-half of the east wall. Another was taken to show
the illumination effects in the west half of the room. This photo-
graph represents the distribution of light and shade on the greater
part of the west wall and adjacent ceiling and includes two of the
fixtures. A third was taken primarily for showing the brightness
measurements of all surfaces having a very high or very low
brilliancy in the field of view of the observer. To have carried
out this program in full in the present work would have required
the insertion here of eighteen photographs. The amount of
difference in the distribution of light and shade for the different
reflectors was much too small to warrant this. It has in fact been
deemed sufficient to include in this paper photographs for only the
second and third of these positions and for only two of the sets
of reflectors used, — the most opaque and the least opaque. The
photographs for the second position are shown in Figs. 2 and 3 ;
for the third, in 4 and 5. In representing the brightness measure-
ments in Figs. 4 and 5, the spot measured is marked by a letter
and the numerical value of the brightness measurement in candle-
power per square inch is printed near by. The spots are lettered
for convenience of reference in the tables of brightness measure-
ments. The photographs were taken from a point directly be-
hind the position of the observer as near to the south wall of the
room as was possible ; and although not all of the observer's field
of view is covered by the brightness measurements made, owing
to the narrow field of the camera as compared with the binocular
field, still the order of magnitude of brightness differences present
in the field of view is well represented by these measurements.
In Tables IV and V are given the brightness measurements of
the room for the six sets of reflectors. These tables also include
the letters identifying the measurements with the spots measured
as shown in Figs. 4 and 5. The distribution of light and shade
in the room was so similar for the different sets of reflectors that
the spots measured have approximately the same location for
each set of reflectors. Two sets of measurements were made
of the brightness of the reflectors, — one with the opening of the
i\ bio
Fig. 2.— Showing the illumination of the west wall of the room, Reflector I.
Fig. 3.-Showing the illumination of the west wall of the room, Reflector VI.
Fig. 4- — Showing the illumination effects in the north end of the room, Reflector I;
and the brightness measurements of all surfaces having a very high or a very low-
brilliancy. This photograph was taken from a point directly behind the observer
as near to the south wall of the room as was possible, and comprehends as much
of the observer's field of view as could be included in the field of the camera.
■ona
T
■ ■""'" -0,0
c s>
.0107 '°'*~>. ""«
a'
£
■ *zu
A
-JO
F
■aoi
A a 1
r?
1
-,-d
-r
K
LjJu
rirj-
■H^Dl':
Jnfcii
wmm
mm\
mmmmilH£^^^f
ri l
mmm,\
"•*'" * 11^3^ %
W. gmtti
Fig. 5. — .Showing the illumination effects in the north end of the room, Reflector VI;
and the brightness measurements of all surfaces having a very high or a very low
brilliancy. This photograph was taken from a point directly behind the observer
as near to the south wall of the room as was possible, and comprehends as much
of the observer's field of view as could be included in the field of the camera.
FERREE AND RAND: EXPERIMENTS ON THE EYE 1 107
illuminometer close to the reflector and the other with the opening
as nearly as possible in the position of the observer when making
the test. In the former case the receiving arm was turned normal
to the surface measured and the instrument was supported in
such a position that the opening was about 4 in. (10.16 cm.) from
this surface. The surfaces of some of the reflectors presented so
much unevenness of brightness that overlapping measurements
were made and an average taken. These average values are given
in Table IV. In Table V is given the brightness of the reflectors
as measured from the position of the observer. These measure-
ments were taken of the reflectors at outlets A, B and C (Fig. i)
for each of the six installations. A comparison of these measure-
ments will show that reflector B has in each case a higher value
than reflector A, and C a higher value than B. Whether or not
this can be wholly accounted for because the reflectors were not
perfect diffusers we are not prepared to say. That is, the angle
subtended by reflector A at the point of observation was less than
that subtended by B, and by B less than that subtended by C;
so that at the distance at which these reflectors was viewed ap-
proximately all of A occupied the field of the illuminometer in
making the brightness match, while only the brighter central
portions of B and C were comprehended in this field, still less of
the duller periphery being included for C than for B.
In Tables VI and VII, are shown some prominent ratios of
surface brightness for the six sets of reflectors. In compiling
these ratios it has been considered important to make a compara-
tive showing for the different types of reflectors (a) of the
extremes of surface brightness and (b) of the relation of the
brilliancy of objects in the surrounding field to the surface bright-
ness at the point of work. Extremes of surface brightness are
shown by giving the ratios between surfaces of the first, second,
third, etc., order of brilliancy and the lowest order of brilliancy;
and the comparison of the brilliancy of objects in the surrounding
field to the brightness at the point of work by giving the ratios
of the surfaces of the first, second, and third order of brilliancy
to the brightness of the test card and the reading page in the
working position.
II08 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
TABLE IV.
Showing the brightness measurements in candlepower per square inch for
the surfaces A, B, C, D, etc. (Figs. 4 and 5), the test card and reading
page. These measurements were taken with the illuminometer close to the
surface measured and with its receiving arm normal to this surface.
Surface Reflector Reflector Reflector Reflector Reflector Reflector
measured type I. type II type III type IV type V type VI
A O.264 O.361 O.392 0.614 0.848 0.920
B O.030 0.01985 0.024 0.0IOI 0.0137 0.0193
C 0.029 0.021 0.021 0.0123 0.0166 0.0156
D 0.0193 0.0106 0.0075 0.0070 0.00767 0.0107
F 0.00238 0.00246 0.00229 0.00282 0.00255 0.0026
F 0.0034 0.00394 0.0034 0.00396 0.00396 0.00396
G 0.0040 0.00392 0.0042 0.00497 0.00418 0.00458
H 0.00414 0.00396 0.0044 0.00506 0.0043 0.00466
I 0.0044 0.00402 0.00453 0.00528 0.0042 0.00484
J 0.00163 o.ocii 0.00128 0.00141 0.00123 0.00163
K 0.0036 0.00387 0.00414 0.0044 0.00425 0.00414
L 0.0023 0.00224 0.00282 0.00299 0.00273 0.00299
M 0.00458 0.00405 0.00484 0.0052 0.00427 0.00506
N 0.00277 0.00216 0.00216 0.00334 0.00268 0.00268
0 0.00348 0.00299 0.00462 0.00361 0.00361 0.00365
p 0.0037 0.00312 0.00506 0.00409 0.0037 0.00397
Q 0.00097 0.00083 0.00106 0.00099 0.000924 0.00106
R 0.00199 0.0029 0.00207 0.00220 0.00246 0.00238
Test card. 0.00312 0.00308 0.00308 0.00317 0.00312 0.00317
Reading
page
hori-
zontal-- 0.00528 0.00497 0.00506 0.0052 0.00484 0.00484
Reading
page
45° po-
sition.. 0.00352 0.00348 0.00352 0.00348 0.00334 0.00339
TABLE V.
Showing the brightness measurements in candlepower per square inch of
the reflectors used when the measurements are made from the position oc-
cupied by the observer during the test. In these measurements the receiving
arm of the illuminometer was placed as nearly as possible in the position of
the observer's eye during the test, and was pointed at the reflector. The
position of the reflector in each case is shown by the letters A, B and C in
Fig. 1.
Position of Reflector Reflector Reflector Reflector Reflector Reflector
reflector type I type II type III type IV type V type VI
A 0.II9 O.156 O.180 O.2325 O.327 O.382
B 0.1755 0.1913 0.2025 0.2535 0.338 0.405
C 0.2025 0.338 0.397 0.544 0.722 0.830
FERREE AND RAND: EXPERIMENTS ON THE EYE IIO9
Supplementary to Tables IV, VI and VII we have computed
for the six types of reflector the mean variation of the several
brightness values from their average values. While important
from the standpoint of showing the variations from the mean for
the different types of reflector, such a comparison is, however,
probably not so important from the standpoint of the eye as are
the comparisons given in Tables IV to VII. That is, from the
standpoint of the effect on the eye it is probably more important
to give a representation of the brightness of individual surfaces,
more especially of surfaces showing extremes of brightness, than
it is to give the mean variation from the average brightness of all
the surfaces. In order to make possible the comparison with and
without the reflector and the spot above the reflector, the table is
made to show separately the mean variation of the following
measurements: (a) for all: (&) for all but the reflector; and
(c) for all but the reflector and the spot above the reflector.
Results are given in Table VIII.
As was stated earlier in the paper the effect of a harmful in-
stallation on the ability of the eye to maintain its efficiency for a
period of work varies with the position of the observer in the
room. In the former work the tests were made at four positions,
one in which six fixtures were in the field of view ; one in which
four were in the field of view ; one in which two were in the field
of view; and one in which none was in the field of view. This
variation of the position in which the observation is made accom-
plishes two purposes : ( 1 ) it gives us a more representative idea
of the difference of the effect on the eye of the six types of light-
ing used; and (2) it shows the effect of varying the number of
surfaces in the field of view showing brightness differences, par-
ticularly the number of primary sources. So far we have been
able to conduct the tests for the reflectors used in this work at
only one of these positions, namely, the one with six reflectors
in the field of view.6 Later we expect to repeat the tests for
at least a part of these reflectors at the other three positions.
The results for the effect on the eye are given in Table IX.7
The values given in this table are averaged in each case from
the results of 6 three-hour tests and are typical of the results
obtained for all of our observers. In order to show the repro-
I IIO TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
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1 1 12 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
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FERREE AND RAND: EXPERIMENTS ON THE EYE 1 1 13
ducibility of the results obtained and that the variations produced
by the changes in lighting effects are much greater than the vari-
ations in the test itself, subject to all the variable factors which
may influence it, the mean variation from the average result has
been computed in each case. The value of this in per cent, is
given in column 15.8
TABLE VIII.
Compiled from Table IV to show the mean variations in surface bright-
ness for the six types of reflector used.
Division A.
Percentage
Mean variation of mean variation
for the three reflectors for the three reflectors
Reflector type Reflector type
Measurements considered I II III I II HI
All 0.02885 0.0373 0.0405 134.8 148.0 148.4
All but the reflector 0.00667 0.00412 0.00411 93.2 75.3 70.3
All but the reflector and
the spots above the re-
flector 0.000917 0.000884 0.0012 29.5 29.7 35.8
Division B.
Percentage
Mean variation of mean variation
for the three reflectors for the three reflectors
Reflector type Reflector type
Measurements considered IV V VI IV V VI
All 0.06494 0.08852 O.09597 168.O 170.8 170.5
All but the reflector 0.0020 0.00274 0.00342 42.4 56.0 62.0
All but the reflector and
the spots above the re-
flector 0.00111 0.000964 0.00104 30.9 30.0 30.2
In Chart i a graphic representation is made of the results of
this table. In constructing this chart, the total length of the test
period is plotted along the abscissa, and the ratio of the time the
test object is seen clear to the time it is seen blurred in the three-
minute records before and after work is plotted along the ordin-
ate. Each one of the large squares along the abscissa represents
one hour of the test period, and along the ordinate an integer of
the ratio.
So far in all our work we have shown for the sake of complete-
ness of representation the gradation of surface brightness in
three ways. — (i) Brightness measurements of prominent sur-
faces have been made. (2) Ratios have been given between
surfaces of the first, second, third, etc., order of brilliancy and
surfaces of the lowest order of brilliancy; and between sur-
1 1 14 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
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FERREE AND RAND: EXPERIMENTS ON THE EYE 1 1 15
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IIl6 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
faces of the first, second and third order of brilliancy and the
brightness at the point of work. And (3) the mean variation
from the average and the percentage of mean variation have been
shown. In the consideration of these specifications, a number of
CHART I.
Showing the tendency of the six types of reflectors to cause loss of
visual efficiency, or power to sustain clear seeing. Ratio time clear to
time blurred is plotted against length of test period.
Foot-candles
Reflector
Type I . .
Type II .
Type III
Type IV
Type V .
Type VI
Volts
III
IIO
107.5
105.5
105.5
107.5
Horizontal
Vertical
45°
4-1
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4.2
I.I6
2.7
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single items might be selected as of possible significance in rela-
tion to the effect on the eye. Among these may be mentioned the
order of magnitude of the highest brilliancies ; the average bril-
liancy; the ratio of the highest to the lowest order of brilliancy;
the ratio of the highest order of brilliancy to the average bril-
FERREE AND RAND: EXPERIMENTS ON THE EYE
II 17
liancy ; the ratio of the average to the lowest order of brilliancy ;
the ratio of the highest order of brilliancy to the brilliancy
at the point of work, (brightness of test card and reading page) ;
etc. In order to see which of these correlate most closely with
the results of the test for tendency to cause loss of efficiency,
CHART II.
Showing the tendency of the six types of reflectors to cause loss of
visual efficiency or power to sustain clear seeing. Percentage drop in ratio
time clear to time blurred is plotted against brightness of reflector in
candlepower per square inch.
Foot-candles
Reflector Volts
Type I in
Type II no
Type III 107.5
Type IV 105.5
Type V 105.5
Type VI 107.5
80
Horizontal
Vertical
45°
Cp. per
sq. in.
4.1
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2.7
O.264
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2.6
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4.2
I.I6
2.7
0.920
curves are constructed in which some of these features are plotted
against the results of the test. These curves are given in Charts
II to IV. In Chart II per cent, loss of efficiency is plotted against
the highest order of brilliancy, namely, the brightness of the re-
flectors. In Chart III and IV are grouped the remainder of the
curves.
Another method of evaluating the results of our test was briefly
IIl8 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
treated of in a discussion of Mr. Cravath's paper by one of the
writers. (The Transactions, 1914, IX, pp. 1051-1053.) In
this method the ratio of the time seen clear to the total time of
the observation is taken as the measure of the ability of the eye
CHART III.
Showing the tendency of the six types of reflectors to cause loss of
visual efficiency or power to sustain clear seeing. In curve A percentage
drop in ratio time clear to time blurred is plotted against ratio of average
brightness to brightness at point of work ; in B, against ratio of lightest
surface to brightness at point of work ; and in C, against average
brightness.
30
40
I5 -""
Y
i\
m
60
40
B
in -
V
/i
71
'5
'70
170
270
80
40
Y^e
h
002 0.04 0.06
to sustain clear seeing at the time the test is taken. For the sake
of comparing this method of evaluation with the one we have used
in the rest of the paper, Charts V and VI have been constructed.
In Chart V length of test period is plotted along the abscissa, and
the ratio of time clear to total time of observation is plotted along
the ordinate. In plotting these lines, one of the larger squares
FERREE AND RAND: EXPERIMENTS ON THE EYE
III9
along the abscissa represents one hour of the test period, and
along the ordinate, 0.1 ratio, time seen clear to the total time of
the observation. That is, in this method of treating the results,
since the ratios, or the quantities to be plotted along the abscissa,
are much smaller than they are in the former method, the scale
CHART IV.
1
Showing the tendency of the six types of reflector to cause loss of
visual efficiency or power to sustain clear seeing. In curve D percentage
drop in ratio time clear to time blurred is plotted against ratio of lightest
surface to average brightness ; in E, against ratio of lightest surface to
darkest surface; and in F, against ratio of average brightness to darkest
surface.
D E
80 1
00 1
m «
Sn
i^
YI <
^
40
n
1/
200
600
000
80
40
m •
711
YJ»>
• 1
20
4-0
B0
has been multiplied by 10 for convenience of representation. In
order that the lines may all start at a common point, the initial
ratios are reduced to 1 as a common standard. In Chart VI, per
cent, loss of efficiency as evaluated by this method is plotted
against intrinsic brilliancy of reflector. As before, intrinsic
brilliancy of reflector is plotted along the abscissa, and per cent.
II20 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
loss of efficiency along the ordinate. A comparison of these re-
sults with the former will show the same order of rating of the
reflectors but a slight change in the position in the scale given to
some of the reflectors. For the purpose of discovering what is
CHART V.
Showing the tendency of the six types of reflectors to cause loss of
visual efficiency or power to sustain clear seeing. Ratio of time clear to
total time of observation is plotted against length of test period.
Foot-candles
Reflector
Type I
Type II
Type III
Type IV
Type V
Type VI
Volts
Horizontal
Vertical
45°
III
4-1
I.I4
2.7
110
3-7
I.I3
2.6
107-5
4.2
I.I6
2.6
105-5
3-8
I.I5
2.5
105.5
3-7
LIS
2.6
107-5
4.2
I.l6
2.7
the best way of treating the results of the tests, several methods
have been employed. Up to and including the present paper,
however, only three of them have been given in print : ratio of
time clear to time blurred, ratio of time clear to total time of
N
FERREE AND RAND: EXPERIMENTS ON THE EYE
II2I
observation, and the per cent, of drop in the ratio time clear to
time blurred. An ultimate decision with regard to what is the
best method of treatment of the results can come, we believe, only
with the consideration of a larger number of cases.
The work was concluded by determining for the six types of
CHART VI.
i
Showing the tendency of the six types of reflectors to cause loss of
visual efficiency or power to sustain clear seeing. Percentage drop in ratio
time clear to total time of observation is plotted against brightness of
reflector in candlepower per square inch.
Foot-candles
Reflector
Type
Type
Type
Type
Type
Type
I .
II
III
IV
V
VI
Volts
Horizontal
Vertical
45°
Cp. per
sq. in.
III
4.1
I.I4
2.7
O.264
110
3-7
I.I3
2.6
O.361
107-5
4.2
I.I6
2.6
0.392
105-5
3-8
LIS
2.5
O.614
105.5
3-7
1. 15
2.6
O.848
107.5
4.2
I.l6
2.7
0.920
installations the relative tendencies to produce ocular discomfort.
As before, two cases were made of this determination, — one when
the eye was at rest, the other when it was at work. For a de-
scription of how the determination is made, and a discussion of
the method that is used, see the Transactions of the I. E .S.,
1913, VIII, pp. 54-58; and 1915, X, pp. 496-501. Space will be
taken here only for presentation of the results. These are given
1 122 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
in Table X. In this table are given also, for the sake of com-
parison, results expressing the tendency of the six types of re-
flectors to cause loss of ability to sustain clear seeing.
APPENDIX.
The reflectors used in this work were supplied by the Holo-
phane Works of the General Electric Co., and are opal glass of
light, medium, and heavy densities. They are all of the bowl
type and of the same size, 8 in. Reflector I is a pressed Sudan
toned brown; reflector II, a blown white glass, toned brown
(experimental); reflector III, a pressed Sudan; reflector IV, a
pressed Druid; reflector V, a blown Veluria; and reflector VI, a
blown white glass (experimental). Reflectors I, III, IV and V
are commercial products, but II and VI are special, inserted in
the series to give gradations in density. As was stated in the
text these reflectors presented considerable unevenness of surface
brightness. This was especially true of the pressed reflectors,
which are smooth on the inside and grooved on the outside. The
glass in these grooves being thinner than in the spaces between,
a very uneven surface brilliancy is given to the reflector. Further,
reflector IV, because of its imperfect diffusion, was quite a little
brighter in the center, at the location of the filament, than at the
top and bottom. In determining the brightness of these reflectors,
overlapping readings were taken and an average obtained.
NOTES.
1 The truth of this should be obvious to any methodological critic. It is in
fact the logical corollary of the application of a new test to a new field. Until a
range of application is made which is reasonably representative of the work for
which the test is designed to be used, a comp'ete description of the test itself, in-
cluding a statement of the factors which may influence its results and full directions
how to use it, cannot possibly be given without more presumption than we care to
exercise. While an attempt to do this might afford a certain amount of specious satis-
faction to the practicing engineer, it would be superficial and incomplete and calculated
to produce trouble in the work of others. When in the opinion of the authors a
sufficient range of work has been covered, a separate paper will again be devoted to
the test method itself in which data collected from all the work will be submitted,
and the adaptability and application of the method to different kinds of work will be
discussed. It is clear, we think, to anyone who has had experience in developing and
applying a new test that this can be done more safely and effectively at the close
of a section of the work which is sufficiently comprehensive to be representative of
the accomplishment of the test, than at its beginning or while the work is yet in
progress. In this later paper data will be submitted also on four types of test devised
by us to detect changes in the functional condition of the retina as the result of
working under different conditions of lighting.
Two points keep coming up, however, with a degree of persistence which may
FERREE AND RAND: EXPERIMENTS ON THE EYE II23
justify a somewhat detailed discussion at this time. The first pertains to the sensi-
tivity of the test to factors extraneous to the conditions that are being tested. The
point was briefly discussed in the original paper on the test and again in the two suc-
ceeding papers. It was brought out more especially in Mr. Cravath's paper and in
the discussions following it. Among .other things it was shown in this paper that by
purposely varying these factors in some extreme way they could be made to influence
the results of the test. The more crucial point was not shown however; namely,
that they operate against the usefulness of the test when the work is done under the
conditions that ordinarily obtain in a well conducted experiment; nor does the paper
contain any evidence that Mr. Cravath thinks 1 this is the case. In our own work a
different plan has been pursued with regard to this point. Instead of trying to find
out what effects could be produced by means of procedures that would not be per-
mitted in making a test, every care has been taken from the beginning to eliminate or
hold as constant as possible all extraneous factors which might influence the general
and muscular efficiency of the eye, and to check 'up the effectiveness of this control
by carefully determining the mean variation in the results for each set of lighting
conditions. This we have considered to be the most direct and feasible plan of con-
ducting the work. In any event, it is obvious that there is no need of futile spec-
ulation concerning the possibilities of influence of these factors, nor of any in-
definiteness either in the discussion or investigation of the point, so long as the
actual value of the influence can be measured by determining the mean variation and
its relative value be estimated by comparing the mean variation with the variations
produced by changing the conditions to be tested. That is, a measure of the absolute
and relative value of these factors is readily available and this measure has been
carefully used at every step in the work. We need scarcely to point out that it is a
well recognized principle of experimentation in comparative work such as we are
doing that as long as the mean variation is safely within the experimental variation,
the method is considered satisfactory for the purpose for which it is being used.
In this connection it may not be out of place to give here a more detailed account
than has yet been given of the method that has been used in selecting and training
observers. Care is exercised in the first place to choose one who has shown a satis-
factory degree of precision in threshold and equality judgments in other optical work
in the laboratory, and whose clinical record shows no uncorrected defects of conse-
quence The observer is then practised on the three minute record under a lighting
condition selected and maintained for the purpose, until a satisfactory degree of
reproducibility is shown. These records are usually run in series of five with a twenty
minute rest interval between each record. So far we have not published the results
of an observer who has not been able to attain a reproducibility in the time seen
clear of 1 per cent, for a series of five records in these preliminary experiments, al-
though this degree of precision is unnecessary unless the observer is being trained for
work in which there are very small differences in the conditions to be tested. Since
these records are run with no change in the lighting conditions and with rest intervals
to prevent general or optical fatigue, they serve primarily as a training in making the
judgment and as a check on the precision of the judgment. In the second stage of
preparation the observer makes a number of three hour tests with records before and
after work for two or more lighting installations, and the mean variation of the
results from the average is determined. Again, if a sufficiently small mean variation
is not shown where there has been no change in the lighting conditions, the observer
is not allowed to take part in the actual work of testing. This last mean variation is
the final preliminary check upon all the factors that may vary under the control im-
posed,— lack of reproducibility in the judgment, variable physical and mental fatigue,
etc. The final check is had in the course of the work itself. That is, a number of
tests are made for each lighting condition of the series to be investigated, and the
mean variation is determined for each and compared with the variations that are
produced by the changes in the conditions to be tested, to find out to what extent
these variations may be ascribed to the changes made and to what extent to the
normal variation of the test. How much larger is the variation which is produced by
changing the lighting conditions than is the normal variation for each condition may
1 124 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
be seen by comparing Columns 14 and 15 of Table IX. In the work of the preceding
papers the excess of the experimental variation over the mean variation was much
greater still as might be expected from the greater differences that were present in
the lighting conditions tested. For example, in five three hour tests for the indirect
system for Position I (see this Transactions 1915, X, pp. 413-426) the mean variation
in per cent was 1.1; for the semi-indirect system it was 1.4; and for the direct system,
1.2; while the percentage drop in the ratio from beginning to close of work for these
systems was respectively, 8.5, 72.3, and 80.9. Similar citations may be made for the
other conditions tested. When one compares in these cases the mean variation with
the magnitude of change of ratio produced by changing the lighting system, it be-
comes obvious how unnecessary has been the concern about the influence of extraneous
factors in case of the work that has as yet been done. In fact, the mean variation
has been so safely within the experimental variation that the writers have not felt
it necessaiy heretofore to make the numerical comparison in print. It is so well
recognized as an experimental principle that the experimental variation shall safely
exceed the mean variation that it has been their custom to give the comparison only
when there exists some grounds for doubt. Heretofore, we have, as a general case,
been working with conditions that produced a large difference in results.
As bearing on another phase of the question of reproducibility, namely, where
a long interval has elapsed between two series of tests, we may cite one example
where two series were taken under the same lighting conditions a year apart, and
the variation in the average per cent, loss of efficiency was only 0.3. In this case a
favorable ligliting system was used, the initial ratios were closely the same, and the
control in general good, although no especial care was taken to make it so more than
what is ordinarily exercised. It is not presented, however, as a typical instance. It
happens to be the only case of which we have a record, where a long interval has
elapsed between two tests.
Moreover, there is nothing in the nature of the test other than its superior sen-
sitivity that should make it more susceptible to the influence of extraneous factors
than any other test of acuity. The principle of the test will be remembered from the
earlier papers. It is merely the conventional acuity test subjected to certain features
of standardization for the sake of greater reproducibility, and made into an endurance
test to give it additional sensitivity. The older test had not been found to be suf-
ficiently sensitive to fatigue conditions to warrant adoption in our work. This test
is in fact not meant to be a fatigue test. It was designed to test the dioptric condition
of the eye, and may be used with more or less success as a test of how far a given
lighting condition is conducive to clear seeing with a maximum of momentary effort;
but it has not the essentials of a fatigue test nor of its converse, the ease with which
clearness of seeing is attained, — which is what is needed primarily for the selection
of lighting conditions for the greater part of the work that we are ordinarily called
upon o do. Almost if not quite as good results, for example, may be gotten with it
after work as before, when there is every other reason to believe the eye has suf-
fered considerable depression in functional power. The reason for this is obvious.
Although greatly fatigued, the eye can, under the spur of the test, be whipped up to
give almost if not quite as good results as the non-fatigued organ when only a
momentary effort is required. (See Column 8, Table IX, and former papers.) If
fatigued, however, it can not be expected to sustain this extra effort for a period of
time. The demonstration of this fact led early in our work to the introduction of
the time element into the test. The principle involved is not a new one. It is
merely the application of a very old and well known one to the work of testing for
optical fatigue. If, for example, a sensitive test is wanted for the detection of
fatigue in a muscle, as good results can not be expected if the test requires only a
momentary effort on the part of the muscle as would be attained if the endurance of
the muscle were taken into account. For our purpose, therefore, the old acuity test
has been made into an endurance test, in which the fatigue or loss of functional
efficiency of the eye is measured by its power to sustain clear seeing for a period
of time. As such it should and does show a sensitivity for detecting fatigue far be-
yond what can be attained by the older and more established test when it is used
FERREE AND RAND: EXPERIMENTS ON THE EYE H25
for that purpose. And being a test which is more sensitive to functional changes in
the eye, it doubtless does show in some proportion to its greater sensitivity more
effect of the indirect as well as of the direct factors that influence acuity; but since
the indirect factors can be subjected to control, while the direct factors are varied,
there is in proportion to the sensitivity .of the test and the control exercised a gain for
the purpose for which the test is used. That this gain is great is shown in all our
work by a comparison of the size of the mean variation with that of the variation
produced by the change in the conditions to be tested.
The second point we wish to discuss here refers to the part played in our ex-
periments by a factor known among psychophysicists as the error of expectation. The
belief that there is a need to take account of this error in sense judgments arises
from the difficulty in keeping the observer in ignorance of the test material and of
a certain amount of the experimental procedure. In our experiments there are just
two points on which the observer has knowledge: namely, the test object and the
lighting conditions or system under which the work is done. All the rest is kept
concealed from him unless the experimenter should in turn serve as observer in which
case his results are checKcd up by tnose of observers who have not served as experi-
menter. We will consider this factor first in relation to the test object. The ob-
server knows what the test object is (the letters li in 8 point type) and is told to
record, for example, when the dot is seen separate from the vertical line in the
letter i. The question at issue then is whether proper account is taken in our ex-
perimental procedure of the influence of expectation on this judgment. The question
can be discussed the most comprehensively perhaps by first considering rather broadly
the status and development of experimental method with regard to this factor. As
we have already intimated, the probable influence of expectation is an inherent diffi-
culty in all sense judgments,— photometric, acuity, threshold, etc. That it can not be
entirely eliminated is, we think, generally conceded as axiomatic. Psychophysicists
have, therefore, turned their attention to attempts to compensate for it, and a need has
been felt to do this in most cases only when the work requires that the determination
be made with a great deal of precision. Different methods may be employed for this
purpose all of which are more or less open to question. The one most frequently
used perhaps, is the method of ascending and descending series. From a consideration
of this method an idea may be had in a general way of all the methods of its class.
Rather than to eliminate or even to lessen the operation of the factor, the purpose of
this method is to control its direction and to plan the experiment in opposing series, so
as to compensate for its influence in the final result. That is, in making a threshold
determination, for example, the series in one case is begun below the threshold,
and the observer is told that the stimulus will be increased until the threshold is
reached; in the other case the procedure is reversed. For the final result an average
is taken of the values so determined on the assumption that expectation in the two
cases will influence the determination by equal amounts in opposite directions. Much
has been said in the literature of psychophysics with regard to whether this method
accomplishes what it is intended to accomplish, and more might be said; but it is
immaterial for our purpose whether it does or not, for it is obvious that it could
not be applied to our 3 minute records, for here the image to be judged rises to the
threshold of discrimination independently of the control of either the observer or the
experimenter. The individual judgments, therefore, could not be arranged m op-
posing series for the purpose of compensation. An entirely different type of method
is to use an objective check on the judgment of the observer, and by this means en-
deavor to weed out from the results the influence of subjective factors. We tried
for several months to devise a means of changing the stimulus in such a way that
an objective check could be had on the registration of the observer without sac-
rificing the principle of the test. Such a change, however, could not be made in
the test object which did not at the same time permit the eye to relax its strain at
the instant of change, which it is obvious destroys the very feature which gives the
test its superior sensitivity. The attempt to get an objective check, however, was
made more for the sake of offsetting possible criticism than it was because of any
belief that it was necessary for the purpose for which the test has so far been used;
1 126 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
for, as we have already stated, a determination of the mean variation for the 3 minute
record, each one of which consists of a number of separate judgments, had shown us
that the influence of expectation as a source of variable error is of negligible con-
sequence. That is, the mean variation is the measure of the aggregate effect of all
the variable factors including expectation, if indeed it be a source of error in the
case under consideration, and it was found to be too small as compared with the
variations produced by the changes in the conditions tested to be the cause for any
concern for the purpose of the work. Moreover, it will be remembered that a knowl-
edge of the test object is given to the observer as one of three changes that were
made in the conventional acuity test to minimize very obvious sources of variable
error, among w.iich were memory and expectation, and to give a greater reproduci-
bility to the judgment. We can do no better probably than quote from the original
discussion. "Visual acuity tests of the Snellen type, especially when used in work
in which it is required to make successive tests on the same person, are open to the
following objections, (a) The judgment is in terms of recognition. A letter may be
recognized when it is not seen clearly. In any judgment based on the recognition of
even a single letter, memory plays an important role. It is, so far as the writer
knows, impossible to standardize this memory factor and to obtain results strictly in
terms of acuteness of vision, (b) The test card is made up of quite a long series
of letters. As the test progresses the letters are memorized more and more completely.
It is practically impossible to eliminate this progressive error when a number of
successive judgments have to be made as is the case before a final result is reached
in any single visual acuity test and as is especially the case when a number of suc-
cessive tests have to be given to the same person, which happens in much of the
work involved in the solution of the problem here proposed (c) The
Snellen series contains quite a large number of letters. The eye is found to fatigue
and vision to blur before the series is completed. This introduces an error which it
is practically impossible to render constant." All of the above errors were elimin-
ated, or at least minimized, in the tests finally adopted by us by changing the type
of judgment and by adopting a simple test object, made up of only two characters,
the letters li in 8 pt. type. In this test the observer's acuity of vision is determined
by the distance at which he can just clearly distinguish the two test objects. In
practise it has come to be a matter of distinguishing whether or not the dot is
separated from the vertical line in the image of the letter i. The results are thus
rendered directly in terms of acuity of vision and the progressive errors due to
memory and expectation are minimized. In this regard the significance of the change
in the type of judgment from recognition to the judgment of the separateness of two
simple objects, e. g., the dot and the line in the letter i, should not be overlooked.
When the criterion is recognition and the task set for the observer is merely to
identify the test object with its name or some memory of it from past experience, as
is the case in the old form of the test, memory and expectation play their maximum
role. Any extraneous clue or a partial discrimination of the object may in fact serve
as a basis for all that is required in the judgment. When, however, the task set
for the observer is a different one and he is required to judge the presence or ab-
sence of a space between the dot and line in the letter i, the role of these factors
is reduced to a minimum, and the task is narrowed down to the judgment of a space
threshold, one of the simplest and most reproducible types of sense judgment. In
short then, a knowledge of the test object is given to the observer as a part of the
modification of the conventional acuity test to minimize the effect of variable factors,
among which memory and expectation play the chief role. And that it has accom-
plished its purpose is abundantly attested by a comparison of the size of the mean
variation given by the test so revised as compared with that given by the older form.
We may add that the letter 1 is used in connection with the letter i for two reasons.
(1) A steadier fixation is given than can be attained by so small an object as the
letter i; and (2) a standard is afforded (an unbroken vertical line) in terms of which
to judge the separateness of the dot from the vertical line in the letter i.
The only other way in which expectation can come into the experiment through
knowledge on the part of the observer is, as we have already stated, through an
FERREE AND RAND: EXPERIMENTS UN THE EVE 112/
awareness of the conditions or lighting system tested. The observer can not work
for three hours under a given lighting installation without being more or less aware
that the same installation is being used as was used before, or a different one. More-
over, we do not see how this unfortunate factor can be completely eliminated unless
imbeciles be used for observers. We wish to point out, however, that there is no
greater liability to harmful influences from this factor in our test than in the older
acuity test or any other that could be applied to the same type of work. We grant
that, in any test that could be used, if observers of strong commercial or other bias
should in two isolated trials get better results for one type of lighting than another,
there might be grounds for suspecting that prejudiced observations were made: but
if each condition were tested a number of times, as has been the case in all of our
work, and a small mean variation were obtained for each series of tests, the result
would look much more like the response of an organism to a constant set of condi-
tions in obedience to physiological law than it would like a voluntary reproduction
guided by prejudice, however strong and constant that prejudice might be. Here
again the size of the mean variation is the check upon the validity of the results,
for it is obvious, we think, even to a novice, that records taken at intervals of from
one to five days could not show a close reproduction if the fidelity of the registration
were in any way interfered with by the wishes or prejudice of the observer. Further-
more, it is only fair to say that it would be difficult to find a group of observers
freer from a direct interest in lighting conditions or a knowledge of their significance
than is the group from which the greater number of our observers are selected.
2 These factors are the evenness of illumination, the evenness of surface bright-
ness, the diffuseness of light, the angle at which the light falls on the work, intensity,
and quality.
3 The problem of installing is probably not the same for the inverted translucent
as for the inverted opaque reflectors. In the latter case the height should be so ad-
justed as to give as nearly as possible an even distribution of surface brightness on the
ceiling, and evenness of illumination on the working plane. In case the inverted
translucent reflectors, however, if the distance from the ceiling is made great enough
in all cases to produce these effects, it may throw the bright reflectors too low in
the field of vision for the highest efficiency and the greatest comfort to the eye. In
this regard the opaque reflectors have the advantage that it is always easier with
them to get the brightest surface in the room out of the zone of most harmful in-
fluence in the field of vision. In later work we expect to conduct a series of ex-
periments with the above reflectors in which the height from the ceiling is the
factor varied.
4 The track along which the test card was moved was parallel to the east and
west walls of the room. When taking the test the observer faced the north wall in
such a position that when the eyes were in the primary position the lines of regard
were parallel with the east and west walls of the room, and approximately normal
to the north and south walls. That is, the head was erect and held in such a position
that the objects in the room, reflectors, etc., fell as symmetrically as was possible
within the field of view. During the three hours of reading which intervened be-
tween the two three minute records, the observer moved just far enough back from
the upright supporting the mouth board to give room for the book to be held, and
to permit of a comfortable reading position. Care was taken to have the eyes sustain
as nearly as was possible the same general relations to the objects of the room
as were sustained when the three minute records were • taken. This could be
done either by holding the head erect, etc., or by tilting slightly backward in the
swivel chair used by the observer and allowing the head to relax a compensating
amount. So far as the direct optical effects are concerned, it would seem to be
immaterial which of these positions is chosen, so long as approximately the same field
of vision is obtained. The latter is usually preferred by the observer as causing less
general fatigue. When taking this position, the book is elevated and held at ap-
19
1 128 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
proximately an angle of 45° (a little nearer to the vertical than this perhaps). The
brightness measurements of the book at this angle and in the horizontal are not
taken, however, so much because of this as to give the brightness of the book in
two fixed representative positions at the point of work. Care is taken to have print
of uniform size and distinctness for use with the three systems and to have a page
which gives a comparatively small amount of specular reflection. Uniformity in these
regards can usually be secured by using numbers of the same journal.
5 It should not be needful to mention that the recording apparatus is screened
from the observer's view while the test is being made. Before photographing, the
screen was removed and the apparatus regrouped.
6 This is the test station shown in Fig. 1, and of the four used in the former
work is the one nearest to the south wall of the room.
7 As has been stated in our former papers, in the consideration of the effect of
a given lighting situation on the ability of the eye to hold its efficiency for a period
of work, the age of the observer and the condition of his eyes should be taken into
account. All of the observers who have been employed by us in this work have been
under 28 years of age. Following is the clinic report of the eyes of the observer
whose results are given in Tables IX and X, made by Dr. Wm. Campbell Posey of
Philadelphia.
Observer R.
With glasses.— Vision of right eye = 20/25. Far muscle test = O y2 esophoria.
Vision of left eye = 20/20. Near muscle test = orthophoria.
Ophthalmoscopic examination.— Right eye = mixed astigmatism, y2 diopter.
Left eye = hyperopic astigmatism, il/2 diopters.
External condition. — Adduction good; eyes slightly divergent under cover;
cornea clear; pupils, 2^ mm.; irides respond equally and freely
to light, accommodation, and convergence stimuli.
Glasses worn during test. — Right eye = — S., 0.50 D. ; — C, 0.37D., x 1600
Left eye = — C, 0.50 D., x 1800
Early in our work the problem arose whether the three minute records before and
after work should be taken in the same room in which the work was done or in
a separate room reserved solely for that purpose. To test this point, work was
done in both ways. It was found that the effects of smaller differences in lighting
conditions could be detected when both the three minute records and the work were
done under the lighting conditions to be tested. That is, the total test procedure,
which includes both the three minute records and the reading, is more sensitive when
it is all done under the conditions to be tested, than when a part of it is done under
these conditions and a part in a separate room. Since the method is more sensi-
tive when the whole procedure is conducted under the lighting conditions to be
tested, we can see no reason why even the purist should demand that a part of it be
done under the conditions to be tested and a part somewhere else, so long as the
results are recognized to be the consequence both of the three minute records and of
the reading. Our purpose, it will be remembered, has been to get a sensitive means
of detecting the relative tendencies of different lighting conditions to cause a loss
in the power of the eye to sustain its ability to see clearly; and the method is more
sensitive when the three minute records, also, are made under the conditions to be
tested. This, we may say, is our chief reason for the practice. A justification, we
believe, is not logically needed. Moreover, the method so conducted is just as
amenable to control and to checks upon its reproducibility, as if it were used in the
less sensitive form. It is, in fact, considerably more amenable to control, for if a
separate room were used for the three minute records, very great care would have
to be exercised to see that it was always illuminated with exactly the same intensity
of light that was used in the room in which the reading was done. If the illumina-
tion were not accurately the same, a period of adaptation would have to be allowed
before the three minute record could be made, which, in case of the record taken
after work, would give the eye opportunity to recover from the fatigue induced by
FERREE AND RAND: EXPERIMENTS ON THE EYE H20,
the work. It is obvious that a great deal of difficulty would be encountered in ac-
curately maintaining this control; and, if it were not so maintained, an error of
considerable consequence would be introduced into the work. In getting control not
only the illumination of the test object must be taken into account, but the bright-
ness of the whole field of vision with its complex distribution of light and shade, for
this conditions the state of adaptation of the paracentral and peripheral portions of
the retina which in turn exerts an influence on the part of the retina that receives
the image of the test object. It may be added also that adaptation effects in the
paracentral and peripheral portions of the retina are stronger and more rapid than in
the central portions. .
In connection with the fact that the three minute records add sensitivity to the
method when they are also taken under the conditions to be tested, we may say
that we are now working on a short method in which three minute records with
proper .rest intervals are used. This test is rougher and less sensitive than the
longer method, but if it can be made satisfactory, it might be more adaptable to
practical work.
8 It will be noted in this table that there is very little variation in the value of
the initial ratios. We noted in each of our preceding papers and again in our dis-
cussion of Mr. Cravath's paper that the sensitivity of the test varies with the ratio of
the working distance of the test object from the observer to the acuity distance.
After considerable investigation of the point, we adopted, as a standard to be at-
tained approximately, a ratio of distances that would give for the initial record a
ratio of time clear to time blurred of 3-5- As might be expected, it is impossible to
get this ratio of 3.5 exactly from any single ratio of working distance to acuity
distance that can be determined in advance of the actual record. But with care a
close approximation may be attained, and since the loss of efficiency is judged from
the amount this ratio is changed from the beginning to the close of work, and not
from the ratio itself, the failure to obtain it does not affect a comparison of the
favorableness of different lighting conditions for the eye, any more than is represented
by its effect on the sensitivity of the test. In short, the variations in this ratio from
test to test form merely one of the group of variable factors, the check upon the effect
of which on the results of the test, is the size of the mean variation; and, so long
as this mean variation is safely within the amount of variation produced by changing
the conditions to be tested, the control may be considered as satisfactory for the
purpose of the work that is being done. That is, when this check is properly exer-
cised, the influence of a variation in this ratio can not possibly be mistaken for the
effect of the condition which is being tested. However, in the course of the deter-
mination of what value of initial ratio should be used, considerable study was made
of the effect of varying the ratio. While space will not permit us to quote largely
from these results here, still an idea may be given in the space at our command of
the order of magnitude of the effect that is produced. That is, we will take three
cases including a range of differences amply great to cover what is ever apt to occu,
in actual work. In the first, the initial ratios were 2. and 3. (difference, 1) ; in th*
second, 2.67 and 5 (difference, 2.33); and in the third, 1.93 and 7-57 (d.fference,
S64). Tne difference in the percentage loss of efficiency for the first case was 1.4;
in the second, 2; and in the third, 1.7. The effect shown in these cases, it will be
observed, is about of the same order as the normal mean variation of the test.
• In order to make a fair comparison between the drop in ratio time clear to time
blurred caused by working under a given lighting condition and the mean variation
of the drop, the percentage drop and the percentage mean variation are both esti-
mated in the above table, also in the citation made in Note 8, p. 1129, on the same
base 3 5 If this comparison had not been wanted especially to show that the mean
variation produced by changing the type of reflector, it would have been more in
accord with custom perhaps to have expressed the mean variation as a percent, of
the mean value of the drop. Computed in this way the value of the mean variation
for Reflectors I-VI would have been in order 5-6 per cent., 1.6 per cent., 1.3 per
cent 33 per cent., 1.2 per cent., 1.4 per cent.; and for the citation in Note 8, they
1 130 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
would have been for the indirect system 4.5 per cent., for the semi-indirect system
0.7 per cent., and for the direct system 0.5 per cent. This method of estimating
the mean variation gives, it will be noted, the largest per cent, variation for the most
favorable lighting condition because the drop in ratio, the base on which the per-
centage is estimated, is the smallest for this condition. The actual variation we have
found as a rule is, as might be expected, the least for the most favorable condition.
DISCUSSION.
Mr. J. R. Cravath : Dr. Ferree calls his test a test "loss of
efficiency of the eye." I think the term "eye- fatigue" is much
briefer and more expressive. The work reported in a previous
paper of Dr. Ferree covered conditions rather widely varied.
The paper we have before us now covers conditions which
come within fairly narrow limits of visible source brightness.
The results have been especially interesting to me as a member
of the Committee on Glare because we have, during the past year,
attempted to formulate or to express certain limits of good prac-
tise which are least conducive to glare. In ordinary interior
illumination, we state in our report, which is soon to be published,
that contrasts of brightness of adjacent surfaces (I mean by
adjacent surfaces, those which are adjacent within the visual
field) should not be over a ratio of one to two hundred, and
preferably not over one to one hundred. That ratio was taken
as the result of an examination of a good deal of data, some of
80
60
u
<
20
n
100 200 300
BRIGHTNESS 0FA-N
Fig. 1.
400
them in previous papers of Dr. Ferree. It was therefore of con-
siderable interest to me to see how the results in the present paper
EXPERIMENTS ON THE EYE 1 131
conform with these limits and in order to do that, I have taken
the ratio between the brightest spot, which of course, is the re-
flector, and the point N on the room photograph a little to the
right of the reflector, and plotted a curve, Fig. 1, corresponding to
Chart II but, instead of using the brightness of the reflector, I
have used the ratio of the brightness of the reflector to the darkest
point along side of it ; that is the point N. The ratios of A to N
under 200 seem to give notably less fatigue than those above
1 to 200, which would confirm the judgment of our committee
as well as the previous results obtained from various sources.
Dr. J. W. ScherESChewsky: I want to congratulate Dr.
Ferree on the extreme care which is evident in all these series of
tests to obtain small mean deviations and secure reproducibility of
results. I wish to call attention, however, to one factor, which
in all probability, will have considerable effect on all tests which
involve muscular action and that is the question of weather con-
ditions. It is plain to all who have read this paper that tests of
this kind such as Dr. Ferree has here published are labors requir-
ing a great deal of care in arranging and carrying out, and it
seems to me that we ought, by all means, in working tests of this
character, to insure, as much as possible that the work shall not
be thrown away because of great variations in the results due to
extraneous factors. Now it seems to me that tests of this kind
ought never to be conducted in very hot weather. The effect of
high degrees of heat and humidity is to reduce the endurance of
muscle. That seems to be plain from Prof. F. Lee's experiments
which were done in the investigations of the New York Ventila-
tion Commission, in which it was found that sections of muscles
removed from animals which had been subjected to high degrees
of temperature and humidity furnished on the average 40 to 50
per cent, less contractions than muscles of animals which had
not been so exposed. Therefore, it seems to me that persons who
conduct tests of this kind in very hot weather would find a great
loss of efficiency of the eye simply from exposure to weather con-
ditions ; so in the future, when we are endeavoring to corroborate
the results of these tests by similar tests, we must take the pre-
caution never to undertake such tests except when the atmos-
pheric conditions are distinctly comfortable.
1 132 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Mr. T. W. Rolph : The data given in this paper are very
valuable to us who have lighting systems to design.
I should like to call attention to the ratio between the brilliancy
of the ceiling and brilliancy of the reflectors as obtained in these
measurements. Reflectors 4 and 5 are typical reflectors of the
class which is most commonly used to-day for semi-indirect light-
ing, and in this particular installation, which does not represent
all installations, but is possibly a typical installation, the ratio
between the brilliancy of the reflector and the brilliancy of the
ceiling is one to fifty, and with reflector 5, one to sixty-one,
taking the brightest point on the ceiling. Those are the re-
flectors which show the greatest eye fatigue, and this shows
us how far we will still have to go in reducing intrinsic brilliancy
in order to get semi-indirect lighting systems which are correct
from the engineering standpoint. Now, reflector No. 3 is a
commercial reflector which is being used to a certain extent for
semi-indirect lighting. It is denser glass and it is harder to sell
than reflectors 4 and 5, so that we who are working for better
lighting in the commercial field have that to contend with. Re-
flector 3 shows a ratio between the brilliancy of the ceiling and
the brilliancy of the reflector of one to sixteen. The densest re-
flector tested has a ratio of one to nine. Three years ago, in a
paper on the "Engineering Principles of Semi-Indirect Lighting,"
I argued that, from the engineering standpoint, the brilliancy of
the reflector in an installation should be approximately the same
as the brilliancy of the ceiling. That was not particularly from
the standpoint of eye protection, but from the standpoint of ob-
taining the maximum diffusion of illumination, arguing that if
we are going to sacrifice the efficiency of direct lighting by in-
stalling semi-indirect systems, we should try to get the maximum
engineering value of the semi-indirect systems, by obtaining max-
imum diffusion, and that this would be obtained when the
brilliancy of the bowl is approximately the same as the brilliancy
of the ceiling. This paper indicates that to obtain good eye-
protection in semi-indirect lighting, we should work to very much
denser glassware or very much lower brilliancy of reflector bowl
than is generally practised to-day. Even a ratio of one to nine,
where the reflector is nine times as bright as the ceiling, shows a
considerable degree of eye fatigue.
EXPERIMENTS ON THE EYE 1133
There is one point I should like to bring out in connection with
the measurement of the intrinsic brilliancy of these reflectors,
and that is merely a suggestion that possibly a good way to obtain
the intrinsic brilliance of a reflector of this character would be to
take the candlepower as determined on the photometer, and the
area of the reflector as determined on a drawing board, and thus
find the candlepower per square inch, rather than to take lumin-
osity measurements of the reflector at various points and average
them. I believe it would be more accurate to take the candle-
power of the reflector and simply divide it by the projected area
in the direction of view.
Mr. J. R. Cravath : This question of what shall be taken as
the criterion of brightness is something that Dr. Ferree evidently
is not sure of, and I don't think any of the rest of us are — I mean,
what particular contrast shall be taken. Mr. Rolph has just
mentioned the contrast of the brightness of the reflector with the
brightness of the ceiling above. Dr. Ferree has given us results
showing the highest brilliancy, that is, the brilliancy of the re-
flector, and the average brilliancy, and the ratio of the highest to
the lowest and the ratio of the highest to the average, the ratio of
the average to the lowest and the ratio of the highest to the bril-
liancy of the point of work. There is such a great deal to be said
in favor of his objection that, possibly, in a case where the subject
is working continuously on desk work or reading that the ratio of
the brightest object in view to the work, that is, to the paper on
which the eye is working, should be the criterion ; because in that
case, the brightest objects in view appear simply on the edge of
the retina most of the time, while the paper is on the center ; but
for most practical purposes, I think perhaps the criterion adopted
by the Committee on Glare of the ratio between the nearest adja-
cent surfaces would answer all practical purposes for the present.
I also want to express the debt that I feel the practical men of the
society owe to the investigators who bring out this kind of data ;
it is exactly what we need to make progress in our work.
Dr. C. E. FerrEE (In reply) : I suggested in a former paper
that, theoretically considered, better results should be gotten with
the semi-indirect reflector of such a density as to give a surface
brilliancy equal to that of the ceiling spot than are obtained with
1 134 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
the totally indirect reflector. That is, if the reflector is made of
the same brightness as the ceiling spot, the same light flux can be
obtained with a lower intrinsic brilliancy of the brightest surface
than if the light all comes from the ceiling spot because of the
increase of luminous area. This is in agreement, I believe, with
the general tenor of Mr. Rolph's discussion. Unfortunately,
however, I have not yet been able to obtain reflectors of sufficient
density to test the point directly. However, in the work that we
have done, an increase in the density of the reflector, so far as
we have been able to carry the increase with the reflectors sup-
plied us for the purpose, has been accompanied by a consistent
improvement in the effect on the eye. There is one thing to be
claimed, however, in favor of the indirect reflector when all is
said and done. It is easier with it to remove the brightest spot in
the field of vision from the zone of harmful influence to the eye,
especially in rooms of the height ordinarily found in dwelling
houses, because with this type of reflector the brightest spot is
always on the ceiling. With reference to the effect of position or
rather height of the brightest spot in the field of vision, it may not
be out of place to anticipate here in slight measure the content of
a future paper. In the work of the present paper the reflectors
were installed 30 inches from the ceiling. This is in accord with
general practise for the installation of totally indirect reflectors
in rooms of the height of our test room and is considered to give
a favorable distribution of light and shade on the ceiling and a
comparatively even distribution of light on the working plane.
So installed, however, the brightest spot (the reflector) is dropped
well into the field of view, especially at the outlets most removed
from the observer. The question arises, therefore, whether semi-
indirect reflectors should be installed according to the principles
of indirect lighting, direct lighting, or whether some compromise
should be made between the two. We have begun, therefore,
a series of tests in which the distance of the reflector from the
ceiling is varied. So far we have been able to finish the compari-
son for the reflectors of least and greatest density at distances of
30 in. and 15 in. from the ceiling. The 15-in. distance gave
quite considerable improvement in the effect on the eye for the
reflector of least density, but not nearly so much for the reflector
of greatest density. This result suggests that a more careful
EXPERIMENTS ON THE EYE 1 1 35
study should be made of the method of installing semi-indirect re-
flectors differing in density. It would seem that the denser they
are the more nearly they can afford to be installed as indirect re-
flectors and the less dense they are the more nearly they should be
installed as direct reflectors so far as eye effects of the kind re-
vealed by our tests are concerned.
I have no doubt that Dr. Schereschewsky is right about the
probable effect of excessive temperature on the results of tests
such as ours. I am very frank to confess, however, that I never
do anything on a hot day if I can help it ; and I certainly would
not conduct a test when the temperature is excessively high.
Through the greater part of the year the temperature of our test
room is kept within a small variation by thermostat control. If
it is necessary to work on warm days electric fans are used ; but
on no account are tests ever made on hot, humid days. In fact
nearly as much care has been taken, I should say, to secure uni-
formity in temperature control in our work as has been taken to
secure a uniform control of illumination and brightness effects.
I am confident, therefore, that our results so far have not suf-
fered from temperature as a variable factor. If I may digress
here for a moment, I should like to say, with no reference what-
ever to Dr. Schereschewsky, whose discussions I have always
found to be most considerate and intelligently liberal in tone, that
I am becoming somewhat tired of the subject of extraneous
factors. To speculate about their probable influence may be of
considerable cultural value to those who have heretofore thought
little about the subject, but there is no need to worry about their
influence or to stand in the way of reasonable progress when a
gauge on the amount of their influence may be and has been had
at every step in the work. In this latter connection I refer to a care-
ful determination of the mean or average variation. If this is done
as it has been done at every step in the training of the observer ;
if moreover it is done for each condition tested and a comparison
made of its amount with the amount of variation produced by
changing the condition tested; exact knowledge is had in every
case whether or not the results obtained are significant. The
subject of gauging the influence of variable factors is too old and
has been too carefully worked out to justify the raising in any
1 136 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
scientific body of as much elementary discussion as has been
raised with regard to it in this Society. The procedure in general
is very simple and straightforward. Train the observer on every
feature of the test method with careful attention to the size of
the mean variation. In the actual work determine the mean varia-
tion for each set of conditions tested and compare it with the
variation produced by changing the conditions to be tested. If
its sum for any two sets of conditions is not less than the dif-
ference between the average results obtained for the two con-
ditions these results, it is usually considered, can not be claimed
as significant. I have spent months, for example, in the training
of an observer on the different features of the test method, only
to discard him at the end of that time because a sufficient degree
of precision of record could not be obtained under a constant set
of lighting conditions. Those who have shown in such a course
of training an unsatisfactory degree of precision usually reveal on
examination, I may say, some uncorrected optical defect. Muscle
imbalance more often than any other seems to have been the
defect in the cases which have so far given us trouble. This
may mean that the extrinsic more often than the intrinsic muscles
are the cause of a variable performance on the part of the eye
in tasks such as we have set for it in our tests, but it is also
probable that the occurrence is due to a considerable extent to the
fact that in ophthalmological practise small defects in muscle
balance are more often left uncorrected than are, for example,
refraction defects.
In concluding my comments on this point I think I may be
justified in mentioning that I have spent a greater number of
years than I like to recall in trying to get control of the variable
factors that influence the response of the eye; and that I have
added considerably to the precision of its performance under
experimental conditions, I can only call upon my published work
to testify. It is not likely, therefore, that in the course of de-
veloping a new test I would show such a degree of incaution with
regard to the most elementary and well-known principles of ex-
perimentation as was made the subject of serious and somewhat
pretentious inquiry in the discussions of the paper preceding the
present one, and in the discussions aroused by Mr. Cravath's
paper.
EXPERIMENTS ON THE EYE IX37
I am glad Mr. Cravath has given us still another way of plotting
the results of the tests against brightness effects. It has not
occurred to me, however, to attach any especial importance as a
separate factor to the ratio of the brilliancy of the brightest area
to that of its immediately contiguous surroundings. There are,
for example, only two possible effects that I could conceive to be
due to this relation, neither one of which would seem to me to
warrant making of it a separate factor, (i) It would enhance
by physiological induction in some proportion to the difference
in physical brightness, the brightness of the sensation aroused by
the reflector and thus increase its power to set up muscular strain
by distracting the eye from the adjustment needed for the work
in hand. So considered, however, its action would merely be
that of an auxiliary factor, supplementary to the actual bright-
ness of the reflector. As such it is of course of a great deal of
importance, greater perhaps, for example, that the relation of
lightest to darkest surface, as brightnesses are graded in a room
ordinarily well illuminated. In short it would seem to me that the
point of reference in determining the relations that are of im-
portance to the eye is the brightness at the point of work. Any
extreme deviation above or below this brightness, especially
above, or anything that would make these deviations conspicuous
to vision would seem to me to be of prime importance. I would,
therefore, consider it an important addition to our present
method of specifying brightness effects to give more detailed
measurements, so far as is practicable, of the surroundings im-
mediately contiguous to the brightest spot, because the effect of
that spot upon sensation is to an important degree dependent
upon the immediate surroundings; but I would by no means be
willing to make these measurements and that of the brightest spot
the sole specification of brightness effects, as Mr. Cravath sug-
gests might be sufficient for our present needs. Moreover, it must
not be overlooked in this connection that a curve plotted on a
basis of the ratio of A, brightness of the reflector, to N for the
different conditions tested must give a curve very similar to that
plotted on the basis of the brightness of the reflectors alone, for
N does not vary greatly from a constant value for the six sets of
reflectors we have used. Obviously, therefore, cognizance should
be taken of this fact before too much general importance is attn-
1 138 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
buted to this ratio as a separate factor from the shape of the
curve plotted by Mr. Cravath for this particular set of conditions.
(2) There might, it is conceivable, be some unknown effect on
the retina which directly depresses its functional power or in-
directly disturbs the adjustment of the eye. I have, however,
already tested quite extensively the tendency of different lighting
conditions to depress the functional power of the retina for as
much as ten hours of continuous work and have found reason to
believe that very little indeed of our results for the tests for loss
of efficiency could be ascribed to a depression of retinal function.
There are four ways, I may say, in which a change in the func-
tional activity of the retina may be manifested: (a) a change in
sensitivity to color and brightness; (b) a change in lag or the
time required for the sensation to reach its maximum; (c) a
change in the susceptibility to fatigue or exhaustion, measured by
rate of exhaustion; and (d) a change in the power of recovery,
measured by rate of recovery. All of these points were covered
in the tests mentioned above. Short of such an investigation a
complete record can not be given of the functional state of the
retina at any time or as the result of any condition or set of
conditions to which it may be subjected. But when such tests
have been conducted for a period of exposure of the eye to the
conditions tested more than three times as long as was used in the
tests for loss of efficiency, it would seem reasonable to conclude
that the results of this latter test could not be ascribed to any
considerable extent to a depression of retinal activity.
Mr. Cravath has always quarreled with me over what the test
should be called and perhaps on good grounds. If "fatigue" is a
more palatable term to the engineer than "loss of efficiency," I am
quite willing that the test shall be called a fatigue test. I have
in fact called it that part of the time myself. My reason for calling
it something else in the beginning was primarily one of pro-
fession. Among men in physiological and psychological optics
the term fatigue as applied to the eye has been, since the days of
Fechner and Helmholtz, a technical term connotating a retinal
condition. It was chiefly to avoid the chance of confusion with
the narrower usage of fatigue that I chose the broader term loss
of efficiency as a brief designation of what is really tested, namely,
the loss in the power of the eye to sustain clear seeing.
EXPERIMENTS ON THE EYE 1139
DISCUSSION.*
Mr. J. R. Cravath (Communicated) : To my mind this work
of Dr. Ferree's as reported in his paper and at previous conven-
tions of the Society is of great and far reaching importance.
Before we can deal intelligently with problems of illumination we
must have methods of measuring the effect of different kinds of
illumination upon the eye. Methods devised previous to the
Ferree test were generally admitted to be unsatisfactory in that
they took no account of the fatiguing effect of continuous work
under given conditions. It will be noted that Prof. Ferree refers
to his test as one to determine the "efficiency of the eye" while
I have usedf the term "eye fatigue" instead of "eye efficiency."
It is of course the privilege of the originator of a method to
apply whatever descriptive terms he wishes to the method, but it
appears to me that "eye fatigue" expresses more nearly what is
really brought out by the Ferree test and conveys a more definite
meaning to the majority of those not intimately in touch with this
kind of work. In connection with Dr. Ferree's results on mov-
ing pictures, it has been my observation that some moving picture
shows are so well equipped and operated that the pictures are
free from flicker and vibration and there is very little conscious
eyestrain, while others using worn out films and making no effort
to get steady light or to prevent vibration of the machine produce
pictures which are very trying to the eyes. I should suppose
that a picture show in a suburb like Bryn Mawr would be
obliged to maintain a high standard of service as compared with
many others throughout the country and that probably Dr. Fer-
ree's results on moving picture shows might show fatigue rather
less than the average.
Dr. Nelson M. Black (Communicated) : The Illuminating
Engineering Society is to be congratulated that the carrying out
of a series of investigations of such magnitude has been under
the direction of such scientific and painstaking observers as the
* The following discussion while it applies somewhat to the foregoing paper refers
more particularly to a paper entitled "Further Experiments on the Efficiency of the
Eye LTnder Different Conditions of Lighting" by C. E. Ferree and G. Rand, which
appears on pp. 448-501, vol. X, of the Transactions of the I. E. S.
t Cravath, J. R., Some Experiments with the Ferree Test for Eye Fatigue ; Trans.
I. E. S., vol. IX, p. 1033.
1 140 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
authors. The mass of data is almost appalling but the deductions
made are clear, concise and very important.
The comparison of the loss in efficiency of the eye when the
observer is in the different positions in the room and the eyes
are subjected to the varying degrees of surface brightness of
objects within the field of view with the three different sources
of illumination is most interesting and instructive. The deduc-
tions from the series of experiments, that the scale of brightness
magnitude and the illumination effects for the indirect system is
very close to what the eye is adapted to stand without loss of
efficiency, is most important and could be taken as a standard
in determining the amount of surface brightness of objects allow-
able in lighting installations of any character.
Another important point is that the position of the observer in
the room does not seem to materially affect ocular efficiency under
the indirect system, especially when one considers that the illumi-
nation of the working surface remains approximately the same
with all systems.
The result of the experiments conducted with the eye shades
with dark and light lining are in accord with those obtained by
Ives and Luckiesh in their investigations of the influence of the
direction of light on ocular comfort, i. e., that the most pleasant
landscape to view seemed to be one in which there was a prepon-
derance of brightness in the sky, with a foreground showing
various degrees of light and shade.
The authors state "it is a question whether any practical good
can accrue to the practise of lighting from a knowledge of just
what part of the visual apparatus it is that falls off in function
as the result of an unfavorable condition of lighting." It would
seem that this is of prime importance.
The result of the investigation of the effect of the three systems
of lighting upon the factors mentioned as involved in clear see-
ing, i. e.t the sensitivity of the eye to colored and white light and
the ability to make fine discriminations and accommodation, will
be awaited with interest.
Dr. Walter B. Lancaster (Communicated) : Is it not
increasingly clear as each successive paper in this series appears
that Prof. Ferree and Dr. Rand are more successfully solv-
EXPERIMENTS ON THE EYE II4I
ing these problems they have undertaken than any investi-
gators so far in the field ? It is not to be expected that we should
agree with all their interpretations of their results. The import-
ant thing is that their methods seem to give consistent and repro-
ducible results in their hands.
I am glad to see that they have apparently abandoned their
view that the first of the three tests, is a test of the efficiency of
the accommodation and now speak of it as "a test of the ability
of the eye to hold its efficiency for a period of work," and as
"a test for loss of efficiency for clear seeing;" that is they do not
commit themselves to any theory of how the test works. As a
result of the few trials I have made of the test on myself and
half a dozen other observers, I am convinced that the accommo-
dation has nothing to do with the blurring but that it is a retinal
affair and depends chiefly on steadiness of fixation — immobility
of the eye, and that in turn on attention, to a by-no-means-negli-
gible degree. However, this is a minor matter, the important
question being, does it give results when applied to problems of
the hygiene of the eye.
Their observation on eye-shades with light and dark linings
are very convincing and important (Table XXV, page 500), since
they agree so well with what was to be expected theoretically but
contradict the popular view. This popular view will die hard
like the popular view of the importance of shielding the eyes by
wearing glasses impervious to ultra-violet light.
The results of tests on moving pictures are also important
since, while every one knew that bad moving pictures are very
fatiguing, few suspected that good moving pictures were so
harmless as shown by chart VIII.
The results of specular versus diffuse reflection (Chart V,
page 485), do not show as great a falling off in efficiency under
specular reflection as might have been expected. Doubtless this
is due to the fact that so small a percentage of the total illumina-
tion of the test object was specular under the conditions of this
particular experiment. The angle at which the light falls on the
work is more important than these figures would imply. This
is strikingly shown by some facts to be found in Table XX, viz.,
even after three hours work under diffuse illumination the ratio
1 142 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
time clear to time blurred (3.18) is the same as the ratio at the
very beginning of work under specular reflection. This may not
be a legitimate inference to be drawn from the table. I should
be glad to have this matter made clear. For example, Table
XIII, p. 473, gives a column of these ratios for different inten-
sities and at the beginning of work these are 3, 5, 3.5, 4, 2.1, 4.8
for the six different intensities tried. Why should there be such
an enormous difference at the beginning of the work at 9 a. m?
Compare footnote on p. 461, which speaks of a variation of
1 per cent, or less. What factors are responsible for these wide
differences in the initial values granting that the ratios between
the initial and terminal values are not so variable? It is the
ratios that are most important but the other figures are not with-
out significance.
The new test for fixation is of interest to ophthalmologists but
will probably not meet with universal acceptance by them. It
appears to be a test for maintaining binocular fusion under forced
convergence. What a variable thing this is with different sub-
jects, all ophthalmologists know. With selected and trained ob-
servers it might none the less prove a useful test. My present
feeling is that the first test is a better test of fixation (monocular
of course). Additional data as to the conditions of this new test
would be very acceptable. Convergence with this stereoscope at
18 is equal to that convergence as ordinarily tested say in meter
angles or by Duane's method or even by measuring simply the
distance from the eyes to the nearest point at which an object
can be seen single. The data quoted from Dr. Posey are ob-
viously contradictory and therefore probably misprints. The
nearer the eye the object is placed the lower the ratio should be,
yet Table XXI, page 489, shows the ratio at the beginning of work
when the object was at 20 to have been 5.66, though the illumina-
tion was less favorable, while the ratio at 22 was 3.7 in one case
and 3.6 in the other. On its surface this indicates inconsistency
in the test of the same description as the inconsistency in Table
XIII mentioned above.
The authors call attention to the significant fact that Chart I
shows for position IV "still a considerable loss of efficiency pro-
duced by the three systems of lighting." They rightly conclude
EXPERIMENTS ON THE EYE ll43
that "evenness of surface brightness is not the only factor in a
lighting situation which may influence the amount of loss of
efficiency sustained by the eye as a result of a period of work."
So also Table XXIII shows that the tendency to produce discom-
fort is still marked if the direct system is used even in position
IV (with all the sources behind the observer and no glaring sur-
faces in front). The time limen is ,57 for direct but 101 for in-
direct, i. e., it takes 75 per cent, longer to produce discomfort
with indirect than with direct illumination when the observer
is reading. I think they do not call attention to the important
fact that when not reading the time limen is not nearly so much
longer for indirect than direct, viz., 235 direct, 265 indirect, is
only 13 per cent, longer than direct. It pleased me very much
to find this feature so well brought out by these tests. As there
is no reason to believe the observers were on the watch for it,
it cannot be attributed to expectant attention, as it might have
been if I had reported it, for it is what I should have expected
from my personal experiences and sensations with different ways,
of lighting, though high authorities in illumination do not agree
with me. I believe that even if the sources are all out of sight
and the brightness of the surface of the book is the same in both
cases the eyes will feel more discomfort and loss of efficiency when
the light is not diffuse but comes from a relatively small source
and therefore one of high brilliancy. In other words while it is
an enormous advance toward comfort to put the direct source
behind and so out of sight of the reader it still leaves much to be
desired if the source is one of high intrinsic brilliancy and there-
fore small and relatively concentrated. For many years I have
given my patients a rough and ready test to determine whether
their lighting was bad. If a pencil is held a few inches from the
book the shadow, if the lighting is good, should be blurred and
indistinct as from a north window. In proportion as it is sharp
and defined, the source is small and of high brilliancy and the
illumination is harsh. In the experiment above, in position IV,
the shadows cast on the page when reading under the direct sys-
tem would be markedly different from the shadows cast in the
same position under the indirect system. With the observer not
reading but looking at the wall in front of him this factor would
become subordinate.
20
1 144 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
Dr. Percy W. Cobb : We have presented to us in this paper1
descriptions of various lighting installations with detailed photo-
metric data, as well as descriptions of other sets of conditions
under which the eye is called upon to work; and alongside of
these the results of a test from which conclusions are drawn as
to the loss efficiency of the eye resulting from a period of work
under each of these several conditions. This seems to me to sum
up the tendency of the paper in spite of the disclaimer which
appears in the last paragraph to the effect that "the purpose has
been primarily to procure methods of working and to find out, as
broadly as one may, the applicability of these methods to the
problems surrounding the hygiene of the eye."
The quotation suggests to me an important omission on the
part of the authors, all the more likely to be overlooked because
of the completeness of description in other respects; and I wish
here to raise the question : How far may the results of the test
as applied be trusted as a true measure of the loss of efficiency of
the eye?
It is to be remembered that the test is original with one of the
authors and has not, with one exception, been used by any one
else. The work done with it has almost entirely been confined to
its application, as in the present paper, to the eye before and
after a period of work under specified conditions. The mode of
procedure has been described but nowhere have we had any full
and detailed account as to its susceptibility to influences other
than the state of efficiency or of fatigue of the eye. Such in-
formation as we have on this latter question is limited to a few
general statements which have appeared from time to time in the
course of the papers of one of the authors and since the bulk of
the work under discussion is taken up with the reporting of the
results of the test under the diverse conditions of the experiments,
it seems to me that we have the right to ask for much more
convincing proof than we have as yet had that the results truly
indicate loss of efficiency of the eye.
Photometrists will no doubt agree that in the photometry of
lights of identical spectral character (or identical color) one may
reproduce his own results to within a fraction of one per cent.
The eye can equate to within about that limit of accuracy. If,
however, we wish to know what are the fluctuations in the sensi-
EXPERIMENTS ON THE EYE 1 145
tivity of the observer's eye while the measurements are in pro-
gress, we see at once that they are included in that fraction of
one per cent., and the mean deviation of the results from their
mean or the probable error may either of them be taken, for
purposes of comparison, as the index of such fluctuations.
Now the method that we are at present considering measures
fluctuations of the sensitivity of the eye. In footnote 14, page 461
it is stated that five separate tests of three minutes duration
on the same observer taken with twenty minute rest-intervals,
and taken under identical conditions, gave results whose varia-
tions always fell within the limit of one per cent.2 It is to be
remembered that the analogy to this is not the accuracy with
which the photometrist may reproduce his measurement, but the
accuracy with which he may reproduce his probable error or his
mean variation.
It may be that this analogy is not permissible in the present
case. The test method is, as far as I know, different from any
procedure heretofore recognized and its limitations may be much
less than those of the methods recognized by psychologists and
sense-physiologists generally. It is nevertheless a matter of
general opinion, I find, among those who have up to the present
conducted investigations of this character on the performance of
sense-organs, that quantitative results are not to be relied on for
reproducibility to within one per cent, when obtained in a few
minutes, and they have been driven to much more time-consuming
and laborious methods to arrive at results which they consider
admissible.
Such methods are of course prohibitive for the purpose of the
authors. They might however be applied once for all to settle
the points on which the method is open to presumptive criticism.
It seems to me that a thorough-going investigation of the method
on this plan, not only as to reproducibility but in other respects,
is not only possible but much to be desired by those to whom the
paper is addressed.
There is another point on which there seems to me to be room
for more than one opinion. That is, that in the application of
the test as used by the authors of the paper the observer is in full
knowledge of all its details. He knows exactly what the test-
object is that he is looking at, and that it is identically the same
1 146 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
and at the same distance before and after the work-period.
Without any question as to the honesty of the observer in wishing
to report exactly as he sees, I think it will be found, and even
stated by the observer himself in many cases, that he has the
utmost difficulty in keeping his preconceptions separate from his
judgments. I mean this remark to apply not specifically to the
work under discussion but to such work as I have been concerned
with, and in general to quantitative work on the sense-organs.
The newness of the method and the importance of the con-
clusions to be drawn from its results would seem to warrant ex-
perimental justification of this feature of the test for the exact
situation in which the test is used, especially in view of the fact
that the opinion will be found to be fairly general that there
should be one or more factors in the experimental procedure,
unknown to the observer except as, through the particular sense-
channel under investigation, he may get knowledge of them that
shall determine the result of the experiment.3
In making reference to the possibility of the test being subject
to influences other than the state of efficiency or fatigue of the
eye, the fact in mind was that in the greater part of the work
reported in this paper the tests were conducted with the observer
at the same point and under the same lighting conditions as during
the work-period. That is to say, in this portion of the work
the test was not conducted under the same conditions in any two
different experiments whose results are compared. More than
this, from the information at hand I cannot see that the inten-
tion of the authors to conduct the test under eye-conditions iden-
tical with those of the work-period was fulfilled. In footnote 8,
page 453,4 it is stated that during the work-period the book was
held at an angle of 45 ° and it is there also implied that the ob-
server was permitted to assume a comfortable reading position.
From what is said further in this note, and from inspection of
Figs. 2, 3, and 4 it seems clear that the track carrying the test-
card was horizontal. The natural inferences are that the eyes
were directed downward at an angle of about 45 ° during the
work-period, that being probably the most comfortable reading
position under the circumstances as stated, and that for the test
they were raised to a horizontal direction. The book — a large
white area in the visual field — is at the same time removed, and
EXPERIMENTS ON THE EYE IJ47
by the shift of the line of vision the light-source and bright areas
in the upper part of the room are thrown by the amount of that
shift nearer to the center of the visual field. This gives in effect
neither uniform conditions for the test in different experiments ;
nor does it give in any particular experiment like conditions, as
far as the eye is concerned, for the reading period on the one
hand and for the tests conducted befbre and after it on the other.
Now the test, involving as it does continuous fixation of the
small mark on the test-card, does not call for the same perform-
ance on the part of the eye as does reading where fixation is
momentary and continually shifting; and it is by no means cer-
tain that the two processes are equally affected by the conditions.
In other words the difference in the results of the test in any two
of these experiments may be due, in part at least, to the difference
in sensitivity of the test conducted as it is under different con-
ditions.5 It may be said, at any rate, that a reasonable doubt
exists on this point and that nothing has so far been done to es-
tablish the fact in question.
What has been said in the foregoing may be summed up in a
few words. The fact that there is in the test method as used by
the authors no check by which bias on the part of the observers
may be ruled out, and the fact that it has not been shown whether
or not the test is influenced by the variations in the conditions
surrounding its application, throw a reasonable doubt on the
question whether its results truly reflect the loss of efficiency of
the eye.
Such doubt may be due to misapprehension of the facts or to
erroneous premises. I think, however, that the doubt will be
found fairly general among those presumably qualified to under-
stand, and might be cleared away by a thorough-going investiga-
tion of the test-method, based on experimental procedures which
are beyond dispute.
The illuminating engineer can make application of such a test,
provided he has unqualified assurance of its validity, and proper
instruction. For these he must look to the psychologist or the
sense-physiologist. The authors will add immensely to the value
of their work by supplying them.
1 148 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
FOOTNOTES.
1 This discussion applies to the paper of Drs. Ferree and Rand presented at the
Convention of 1914 (these Transactions, Vol. X, pp. 448-501). As for some reason
it could not be published in its proper place it is given here, with such additions in
the form of footnotes as have been found necessary in view of the contents of the
present paper.
- Although the mean variation of the ratio, time clear: time blurred, is men-
tioned in the footnote cited it is to be remarked that this 1 per cent, variation applies
strictly to the time seen clear. The corresponding variation in the ratio will be
found to be 4.5 per cent., assuming 140 seconds in 180 as the average time seen clear.
It is not plain why the results are stated in terms of the ratio, while the mean varia-
tions are given as applying to the time seen clear. This fact throws doubt on the
mode of derivation of the mean variations given in Table IX of the present paper.
3 It is by no means impossible to introduce a variable factor in the test, un-
known to the observer. Such a factor would be furnished by the use, in different
experiments, of slightly different test-cards. These might be made from cards origi-
nally identical by obliterating the space between the i and its dot in varying degrees
with a fine pen. For the individual cards of such a set the reading distances should
be slightly different. They could be so selected as to be used at the same distance
and the difference could reasonably be expected to appear in the results without
being" evident to the observer during the progress of the test. This would give an
answer to the question as to the importance of the factor of expectation in the
observer.
4 See also Note 4 following the present paper. It is difficult to imagine a com-
fortable reading position with the book held at an angle with the vertical unless
the eyes are directed downward from the horizontal to almost the same degree.
5 This contention is frankly admitted in Note 7 at the end of the present paper:
"It was found that the effects of smaller differences in lighting conditions could be
detected when both the three minute records and the work were done under the
lighting conditions to be tested."
It is argued therefrom that the method is thus more sensitive and not open
to objection since the result is a consequence of the tests and the work combined,
done under the lighting conditions to be tested. But how in such a case, to illus-
trate, as is implied in the quotation? If no result is observed when the illumination
conditions for the test are standardized, and a positive result when they are con-
ducted under the conditions to be investigated, it would appear that the result is
logically to be ascribed to the conditions surrounding the tests. There would be no
objection to the inclusion of this effect in the result if there were in practical life
any work that the eyes are called upon to do at all comparable with the effort that
such a test demands; and if the eye conditions were actually, as well as nominally,
identical for the tests and the intervening work-period.
The objection to the standardization of the test-conditions raised by the authors
further on, namely that slight differences in the level of adaptation will materially
affect the results, applies with equal force to the procedure of the authors as in-
dicated by what I have just said. The necessity emphasized for the control of the
"whole field of vision with its complex distribution of light and shade" applies
equally well as an objection to the change in the distribution of light on the retina
brought about by shifting the eyes from the oblique reading position to the horizontal
position demanded by the test. The statement (Note 4) that "Care was taken to
have the eyes sustain as nearly as was possible the same general relations to the ob-
jects of the room " contains nothing to imply that such a shift was avoided.
EXPERIMENTS ON THE EYE 1 149
Dr. C. E. Ferree (In reply) : I agree with Mr. Cravath that
our results for the moving pictures selected probably show less
fatigue than would be shown in the average by a wide testing of
moving picture houses. For example it is stated in the text:
"The tests were conducted in a local theater, selected primarily
because of the favorable conditions that prevailed. The definition
at the screen was good and the pictures were unusually steady
and free from flicker. The conditions were, we think, fairly
representative of what is found in the better class of motion
picture houses." I should like very much for comparative pur-
poses to test the effect produced in some of our lower grade
houses, especially on a Saturday night when frequently the rate
at which the pictures are given to the eye is very much increased.
We hope later to make a more extensive investigation of motion
picture effects. This investigation was made primarily to find
out whether our test would show an effect of motion pictures on
the eye.
Dr. Black says : "The authors state 'It is a question whether
any practical good can accrue to the practise of lighting from a
knowledge of just what part of the visual apparatus it is that falls
off in function as the result of an unfavorable condition of light-
ing.' It would seem that this is of prime importance." I should
have appreciated it very much if Dr. Black had elaborated on this
statement. I should be glad to know the opinion of the opthal-
mologists with regard to the importance of pursuing the analy-
tical study.
I am very glad indeed for many reasons to take into account
anything that Dr. Lancaster may have to say about the work we
are doing. I shall mention only one of these reasons here. Real-
izing from his intimate knowledge of eye testing something of the
difficulties one may expect to find in applying an unfamiliar test,
he made a trip to our laboratory before attempting any work at
all with the test, to find out just how we made the application
ourselves.
Dr. Lancaster says in the first paragraph of his discussion:
"... their methods seem to give consistent and repro-
ducible results in their hands." Apropos of this statement by
Dr. Lancaster a word of comment and explanation may not be
1 150 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
out of place here.1 So far as the test has been applied by us, the
mean variation from test to test has been very much less than
any experimental variation, from which we have drawn differen-
tial conclusions with regard to the relative merits of lighting con-
ditions, and no results have been or will be published as signifi-
cant in a variation of lighting conditions in which the change in
result produced is not safely in excess of the mean variation of
the test. In fact, because of the amount of this excess of the
experimental variation over the mean variation, we have not as
yet felt urged to compile and publish full data on the reproduci-
bility of the test.
Dr. Lancaster says in the second paragraph of his discussion :
"I am glad to see that they (the authors) have apparently
abandoned their view that the first of the three tests is a test of
the efficiency of the accommodation and now speak of it as 'a test
of the ability of the eye to hold its efficiency for a period of work'
and as 'a test for loss of efficiency for clear seeing' ; that is they
do not commit themselves to any theory of how the test works."
I am somewhat puzzled to understand how Dr. Lancaster has
gotten the impression from anything we have published that we
considered the test referred to be of itself anything but a test of
the aggregate loss of functioning of the eye. The test was not
designed to be analytical in nature, but merely to show changes in
the eye's ability to see clearly for the three-minute interval con-
sumed by the test before and after work. This is shown by the
title of the first paper "Tests for the Efficiency of the Eye, etc.,"
and in the discussions of the test in the same paper pp. 45-50 in
which it it always referred to as a test for the efficiency of the
eye not as a test for the efficiency of the accommodation or any
other single function. Indeed on p. 50 of that paper the statement
is made very explicitly. "This ratio as stated earlier in the paper
expresses the efficiency of the eye for clear seeing for an interval
of three minutes at the time at which the test was taken." In
connection with the test for aggregate effect, however, tests de-
signed to be analytical in nature were made, namely, tests for
changes (a) in the response of the retina to colored and colorless
light; (b) in the rate of exhaustion; and (c) for the rate of
recovery of the retina; and (d) for the rate of lag of sensation;
6 See also discussion of Mr. Cravath's paper, Trans. I. E. S., 1914. vol. IX.
EXPERIMENTS ON THE EYE II51
also tests for loss of efficiency of the fixation muscles. It was
only because these tests showed very little if any significant effect
that we suggested very tentatively, subject to the results of a
further test bearing more directly upon the accommodation
muscles, that the results gotten in the general test were due
largely to loss in efficiency of the accommodation muscles. The
first test was not designed to test for losses in power to accom-
modate alone, nor was it used for that purpose. So far as its
relation to the eye is concerned, it was used merely as an explor-
ative test to separate out good from bad hygienic conditions rated
according to an aggregate effect on clear seeing.
Dr. Lancaster further says: "I am convinced that the accom-
modation has nothing to do with the blurring but that it is a
retinal affair and depends chiefly on steadiness of fixation — im-
mobility of the eye, and that in turn on attention to a by-no-
means-negligible degree." It may perhaps be inferred from this
statement that, since the greater amount of blurring takes place
under the conditions which would distract the fixation most and
therefore lead to the greatest unsteadiness of fixation, Dr. Lan-
caster considers that the blurring comes as an effect of unsteady
fixation on the functioning of the retina. This point of view
carries the writer back to a group of problems in the study of
which he spent four years.7 Space cannot be taken here to go into
that work. It is sufficient to say that since the time of Fechner,8
it has been held that involuntary eye-movements, or unsteadi-
ness of fixation, are of prime importance in keeping the retina
from becoming exhausted during the course of a working day.
That is, so far as the functioning of the retina alone is concerned,
unsteadinesss of fixation or movements of the eye both voluntary
and involuntary work for clear seeing, not blurring; and the
lighting system which by the strain it puts on the muscles causes
the greatest unsteadiness of fixation, should be the system which
causes the least and not the greatest blurring in the test following
7 See C. E. Ferree, An Experimental Examination of the Phenomena Usually
Attributed to Fluctuation of Attention, Amer. Jdur. of Psych., 1906, XVII, pp. 79-
121; The Intermittence of Minimal Visual Sensation, ibid, 1908, XIX, pp. 57-130;
The Streaming Phenomnoa, ibid, 1908, XIX, pp. 483-504; The Fluctuation of lumi-
nal Visual Stimuli of Point Area, ibid, 1913, XXIV, pp. 377-410.
'See Fechner, Pogg. Ann., 1838, XUV, p. 525; Helmholtz, Physiol. Optik.,
1896, p. 510; Fick and Gurber, Archiv fur Opthal., 1890, XXXVI, (2), p. 246; Hess,
ibid, 1894, XL, (1), p. 274; MacDougall, Mind, 1902, XL, p. 316; 1903, XIJ, p. 289;
and the present writer, loc. cit.
1 152 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
the period of work. And so it would, as is abundantly shown in
the references cited on the effect of eye-movement on the
functioning of the retina, if the unsteadiness of fixation and ac-
commodation caused by such a lighting system did not also
interfere with the clear imaging of light on the retina that is
needed for clear seeing.9
In paragraph five Dr. Lancaster expresses the belief that while
the major significance should be attached to the change of ratio
of time seen clear to time seen blurred before and after work,
considerable significance should be attached also to the difference
in the value of this ratio before work for the different lighting
conditions. One of the reasons he gives for this is that in Table
XIII, which shows the results for six tests on the effect of
variation of the intensity of light with the indirect system, and of
variation of intrinsic brightness of the ceiling spots above the
reflector produced by using socket extenders with some of the
shorter lamps, these initial ratios seem to vary as much if not
more than the final ratios, or as the change in ratio before and
after work. These initial ratios were respectively 3, 5, 3.5, 4, 2.1,
4.8. If, however, Dr. Lancaster will observe the table closely,
he will see that the ratio of the working distance to the acuity
distance is not the same in all of these cases. The same ratio of
time clear to time blurred should, therefore, not be expected even
were the lighting conditions the same. Whenever, for example,
the working distance has been chosen closer to the eye, propor-
tionate to the acuity distance, a higher ratio of time clear to time
blurred should be expected. This, it will be seen, happened in
all but one of the above cases in spite of differences in lighting
conditions. However, everything else being equal, it is perhaps true
that the more unfavorable lighting condition will cause greater
proportionate blurring in the initial record observation,10 and if
so, the results of this initial observation may have some diagnostic
value. We have, however, never felt it safe to use the results of
9 That is, unsteadiness of accommodation interferes with the clear imaging of
the light on each retina, and unsteadiness of fixation with the imaging on function-
ally corresponding areas of the two retinae. Functionally corresponding is used
here in the usual sense, namely, areas of the two retina which in binocular seeing
combine their images into one. If the images do not fall fairly accurately on these
areas, doubling and consequent blurring result.
10 The above statement is made with reservation. The pornt will be discussed
more fully later.
EXPERIMENTS ON THE EYE 1 1 53
the initial observation in this way because they are, when com-
pared from day to day as they would have to be in this case, the
least reproducible feature of our test. In the way in which we
are accustomed to evaluate our results, the deviation from close
reproducibility of this feature of the test enters into the evaluation
of the favorableness of lighting conditions for the eye no more
than is represented by its comparatively slight effect on the sen-
sitivity of the test. That is, we so conduct our test and evaluate
its results as to give negligible weight to this item, the successful
accomplishment of which is shown in the small mean variation
gotten in the actual work of testing. Dr. Lancaster thinks the
variation of the ratios for the initial test quoted above has all the
more significance when compared with the estimation of the
degree of reproducibility of the 3-minute record given in foot-
note 14, p. 461. Here it is stated that with the practised ob-
servers we used the maximum variation of time clear in five
consecutive records for the fresh eye with a rest interval of
20 minutes between each record has always fallen within 1
per cent, for all the observers whose results have been pub-
lished. The following points will show that little stress should
be laid on this comparison. (1) The reproducibility tests (for
which the 1 per cent, reproducibility was quoted) on the fresh
eye were made with exactly the same ratio of working distance
to acuity distance. In the tests of which Dr. Lancaster quotes
results this ratio was different. (2) The reproducibility tests
were also made always on the same morning with a 20-minute
rest interval under very favorable and always identical rest con-
ditions. The tests referred to by Dr. Lancaster were taken on
different days. And (3) the 1 per cent, deviation in the repro-
ducibility tests were from the average of the time seen clear; the
deviations quoted by Dr. Lancaster were in the ratio time clear to
time blurred.
In the sixth paragraph Dr. Lancaster says : "The new test for
fixation is of interest to ophthalmologists but will probably not
meet with universal acceptance by them. It appears to be a test
for maintaining binocular fusion under forced convergence.
What a variable thing this is with different subjects all ophthal-
mologists know. With selected and trained observers it might
1 154 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
none the less prove a useful test." We do not quite see how its
variability from observer to observer affects the purpose for
which we have used the test. Our purpose is to select practised
observers and see how much the power of each to maintain bin-
ocular combination of images is affected by both the work and the
test under a given lighting condition. The point of comparison
is not at all one of individual differences, but how much for a
given individual the power to maintain the binocular combination
is affected by work under the lighting conditions which are
being tested. I do not think, therefore, that Dr. Lancaster's
point is relevant to the purpose for which the test has been used,
nor can I see that it constitutes any objection to the use of the
test to supplement the tests now used by the ophthalmologist for
the fixation muscles. I have already pointed out in the text that
it may be more important, even in the work of the clinic, to de-
termine the eye's power to sustain co-ordinated muscular action
than it is to determine the maximum pulling power of the indi-
vidual muscles by a momentary effort, for it is obviously the
power to sustain co-ordinated muscular action that is of prime
importance in determining whether the eye, so far as the fixation
muscles are concerned, is able to carry on sustained work. In
fact sustained co-ordination is just what is demanded of the eye in
continuous work. It seemed to me, therefore, that this type of
test more nearly measures what is demanded of the working
eye than do, for example, the ordinary abduction and adduction
tests.
Later in this paragraph, Dr. Lancaster's discussion shows that
he has misunderstood our data. He has apparently understood
the table reading "Distance at which test object is normally
seen single" to mean that nearest point at which it can be seen
single by a maximum effort of convergence. This is given in the
table as 1 8 cm. for the observer used. This distance was not
the nearest point at which the test objects could be seen single
with maximum effort, but the distance at which, as the wording
of the heading indicates, they were most easily held combined.
Therefore, when the test objects are set either nearer to the
eyes or further away, they will be held combined with effort.
The observer whose results are given in Table XXI, in order
EXPERIMENTS ON THE EYE 1 1 55
to put the eyes under strain to combine these images, preferred
to set the objects at a greater rather than a less distance than
18 cm. from the eye. The 22 cm. distance, therefore, should
and did give for the fresh eye a smaller ratio of total time
single to total time double for this observer than the 20 cm. We
should have made it clear in discussing the test that a point either
nearer or further than the most favorable could be used and that
the latter was used in case of the observer whose results were
given in Table XXI. My explanation of the oversight is that I
had always used the other condition myself and had become ac-
customed to think of the test in that way. In explaining this
point we have doubtless also explained the contradiction which
Dr. Lancaster thought to exist between Dr. Posey's clinic data
and the results of Table XXI. We are deeply indebted to Dr.
Lancaster for calling our attention to the point. Either an ex-
planatory footnote should have been appended to the table or
the results of another observer should have been selected.
Dr. C. E. FerrEE (In reply to Dr. Cobb) : In replying to Dr.
Cobb's discussion I am somewhat in doubt whether to consider
it merely a discussion of the paper immediately preceding the
present one or as being intended to apply also to the present
paper. Since it has been revised by appending footnotes which
take into account the contents of the present paper, the natural
presumption is that in as far as the body of the paper is not
modified by these footnotes, what is said is meant to apply to
the present as well as the preceding paper.
In a brief review of the beginning of the discussion I may be
pardoned perhaps for calling attention to the fact that in the
quotation made from our paper in his opening paragraph he
has abstracted from its context just what was favorable for the
point he wished to make and ignored the rest. The quotation
should continue: "While in many places attention has been
called to results that have seemed to have general significance,
the intention has been, in general, to limit all comments and con-
clusions strictly to the conditions under which the work was
done." This in connection with the quotation made seemed to
me at the time to be a fair statement of the case and it seems to
1 156 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
be so to me yet. The conditions under which the work has been
done have been made clear at every point and not the slightest
attempt has been made to draw conclusions beyond these condi-
tions. Moreover, to do this is not in the least degree contradic-
tory to the purpose expressed in the sentence quoted, namely,
"primarily to find out, as broadly as one may, the applicability of
our test method to the problems surrounding the hygiene of the
eye." It was well known, for example, that the work was being
done by methods the precision and applicability of which were
under investigation for each new set of conditions employed.
This investigation, however, I need scarcely to state, was not a
part of the actual work of testing. It was completed and the
observer trained to a satisfactory degree of precision before that
work was begun. That is, not until an observer selected on the
basis of both his freedom from optical defects and a precision
already shown in other work in physiological optics, had also
attained to a satisfactory degree of precision in the 3-minute
record under a given lighting condition and in the 3-hour test
under several conditions, and a careful comparison of results in
the actual work of testing had shown that the variations produced
by changing the conditions to be tested was by a large margin
safely in excess of the mean variation from the average for
each of the conditions tested, were his results accepted as sig-
nificant. Then and not until then were data incorporated into
tables and curves purporting to represent the effect of the con-
ditions tested upon the ability of the eye to sustain clear seeing.
It is clear then, I think, that both of these procedures, the pre-
liminary investigation of the precision and applicability of the
test to each new set of conditions and the actual work of testing
these conditions have been features of our work just as was
stated in the concluding paragraph referred to, and not the latter
alone or predominantly, as was gratuitously inferred by Dr.
Cobb. Furthermore, until a wider range of work is covered we
intend that our purpose shall remain primarily that of finding
out as broadly as we may the applicability of our method to new
conditions ; but that purpose, it is obvious, when satisfied should
not and will not in the least prevent us from doing the actual
testing for these conditions ; and the result for this testing, it is
scarcely needful to say, may reasonably be expected to make up
EXPERIMENTS ON THE EYE 1 157
the larger part of future papers as they have of the papers al-
ready presented, without the liability of anyone's misunderstand-
ing either what has been intended or what has been done.
In his third paragraph Dr. Cobb charges that we have not
published enough data in our papers to insure the reader of the
reliability of the methods employed, and leaves it rather pointedly
to be inferred both here and elsewhere in the discussion that to
the best of his belief sufficient precautions have not been taken
to guard the results against the influence of extraneous factors.
We regret that this charge is not more specific, for then it not
only would have more meaning but it could be answered in
briefer space. However, let us recall (i) just what precautions
have been taken that the influence of variable factors extraneous
to the effect of the conditions tested should not enter into the
conditions of the experiment to an extent that would be harmful
for the purpose for which the experiment was used, and that no
variations produced by such factors should be confused with the
variations produced by changing the conditions to be tested; and
(2) just how much data has been published with regard to these
precautions up to the present time. Before beginning and pre-
liminary to the work the results of which have been published
in our last three papers, a study was made for the express pur-
pose of finding out just what factors would be likely to influence
the results of the work, and methods were devised for controlling
these factors. Obviously a study of the influence of a factor
can be made by varying that factor when all other conditions are
held constant and noting the effect on the results. Such a study
could have gone on endlessly and the presentation of its results
would have consumed endless space. Moreover, such work leads
to nothing once the factors are known and methods have been
devised to control them. That type of investigation of the test
was pursued to some extent, however, by Mr. Cravath, and the
results of his work were published. In our own work instead
of trying to find out at needless length what effects could be pro-
duced by means of a procedure that never would be permitted
in making a test, every care has been taken to control the factors
the possibility of the influence of which had been revealed in
the preliminary experiments ; and the effectiveness of the control
1 1 58 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
was checked up by carefully determining the mean variation of
the results for each set of lighting conditions. The size of this
mean variation is, it is well known, the measure of the net in-
fluence of the factors extraneous to the conditions which are
being tested. When, for example, two lighting systems are being
tested and it is found that the difference in the average result
obtained for the two systems is not greater than the sum of the
mean variations for both, the conclusion can not be certainly
drawn that a significant difference in effect is produced by the
two systems. This method of treating results has been devised
as a gauge on the influence of variable extraneous factors and
should be too well known to need further discussion here. Let
it be sufficient to state that this check upon the absolute and rel-
ative value of the influence of such factors has been carefully
applied at every step in the work. This we have already stated.
We have also given a statement of the care that was exercised
in the selection of observers based both upon their optical con-
dition and the precision they had already shown in other work in
physiological optics; and a very detailed description of the care-
ful method that was used in training the observer separately on
each feature of the test with careful attention to the size of the
mean variation throughout. Short of a paper devoted to the
test, the data that has been published on the above points can
scarcely be considered insufficient. Statements of the precau-
tions that have been taken in the control of the extraneous fac-
tors and in the selection and training of observers have been
published as the need arose in all four papers and amplified both
in the public and written discussions both of our own papers
and Mr. Cravath's. A statement of the standard of precision
to which each observer must attain in the 3-minute records
before he was allowed even to participate in the practise series
of the 3-hour tests was made in connection with the publica-
tion of the second and third papers11 and again in the fourth
paper. A comparison of the mean variation for each lighting
condition with the variation produced by changing the condition
to be tested was given as a regular feature of the presentation
of the results for the work of the fourth paper. Here we are
11 The second and third papers, it will be remembered, were published simul-
taneously.
EXPERIMENTS OX THE EYE 1 159
working with smaller variations in lighting effects and there was
need to show the comparison. In the presentation of the data
of the second and third papers, however, the comparison was
not considered necessary. The changes made in the conditions
tested in that work were so large and the variations produced by
changing the conditions tested so absurdly much greater than the
normal variation for each of the conditions tested that the com-
parison seemed, as I have already said, not only needless but dis-
tinctly ostentatious. A representative numerical statement of the
comparison, however, is given in the fourth paper. Moreover, a
detailed statement will be given in a final paper devoted to the
test. We have taken considerable care to describe the exact con-
ditions under which the work was done, or to give precautions that
were taken to guard against the influence of variable factors.
In the fourth and fifth paragraphs Dr. Cobb compares our work
with photometry in a way that needs not only elucidation but some
correction. There is, for example, absolutely no difference
between the two kinds of work that would make one capable and
the other incapable of precise performance. In photometry a
judgment of brightness equality is employed which may range or
vary through a difference threshold on either side of equality. In
our work a visual acuity judgment is employed which is nothing
more nor less than the judgment of a space threshold. Of the
two the latter is the more precise even when the judgment of
equality is made between two lights of the same composition. A
different use is also made of the judgment. In photometry the
judgment is used to equate the power of two lights to arouse
equal sensations with the eye at a given standard of performance.
In our work the judgment is used to measure the ability of the
eye to hold itself up to a given standard of performance from
beginning to end of a period of work under this or that lighting
condition. In careful work when the photometric judgment is
used to equate the power of two lights to arouse sensations of
equal intensity the observer is first trained to a satisfactory de-
gree of precision in making the judgment before the work of
photometering is done, and this photometering itself is checked
by the degree of reproducibility of the results obtained, or the
size of the mean variation. If, however, the photometric judg-
Il6o TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
ment were used to measure the power of the eye to hold itself up
to a certain standard of performance from the beginning to the
end of a period of work under a given lighting condition, and
we have used it in that way in our work on determining the
ability of the retina to maintain its power to discriminate bright-
ness differences through a period of work under different lighting
conditions, the method of training the observer and the check on
the precision of the work should be carried out just as we have
carried it out in our work on the power of the eye to hold itself
up to a certain standard of acuity. That is, precision is first at-
tained in making the photometric judgment. The observer is then
given a period of training and practise in which the precision is
compared before and after work under a given lighting condition.
As a third step the observer is allowed a period of practise under
different lighting conditions until a satisfactory degree of repro-
ducibility is attained in the figure or ratio expressing a com-
parison either of the sensitivity or the size of the difference thres-
hold before and after work. And lastly in the actual work of
testing, the final results are compiled from a large number of
determinations, and the precision is checked up by the size of the
mean variation. It is, for example, very misleading for Dr.
Cobb to state in reference to our work as he has in the sixth
paragraph :
It is nevertheless a matter of general opinion, I find, among those
who have up to this present time conducted investigations of this char-
acter on the performance of the sense organs, that quantitative results
are not to be relied on for reproducibility to within i per cent., when
obtained in a few minutes, and they have been driven to much more time
consuming, laborious methods to arrive at results which they consider
admissible.
Dr. Cobb points out that the test is original with the authors
and should, because it is so very new, be subjected to probation
and searching criticism before it be given a place in the sun
along with methods hoary and worn with service. Since the
question is raised it might be well to find out just how new in
its essential principles the method really is. Just two features are
involved in the test method, — one is that visual acuity or clear-
ness of seeing may be measured by the smallest visual angle the
eye is able to discriminate; the other, a principle equally old, is
that a loss of efficiency or depression of function in a machine,
EXPERIMENTS ON THE EYE
Il6l
apparatus, or living organ or organism will show out more plainly
when a prolonged rather than a momentary performance is re-
quired. Our intention has been to combine these principles in
their simplest terms into a test of the comparative power of the
eye to sustain its power of clear seeing or aggregate functional
activity under different conditions of lighting and with different
kinds and conditions of use. Allow me to quote from a state-
ment of the principle of the test.
The principle of the test will be remembered from the earlier papers.
It is merely the conventional acuity test subjected to certain features of
standardization for the sake of greater reproducibility and made into an
endurance test to give it additional sensitivity. The older test had not
been found to be sufficiently sensitive to fatigue conditions to warrant
adoption in our work. This test is not in fact meant to be a fatigue test.
It was designed to test the dioptric condition of the eye and may be used
with more or less success perhaps as Dr. Cobb used it "as a test of how
far a given lighting condition is conducive to clear seeing with a maxi-
mum of momentary effort" (provided, however, it is used with a degree
of precision and in connection with a plan of experimentation that will
warrant the drawing of conclusions) ; "but it has not the essentials of a
fatigue test nor of its converse, the ease with which clearness of seeing
is attained, which is what is needed primarily for the selection of lighting
conditions for the greater part of the work that we are ordinarily called
upon to do. Almost if not quite as good results may be gotten with it,
for example, after work as before, when there is every other reason to
believe the eye has suffered considerable depression in functional power.
The reason for this is obvious. Although greatly fatigued the eye can,
under the spur of the test, be whipped up to give almost if not quite as
good results as the non-fatigued organ when only a momentary effort is
required. If fatigued, however, it cannot be expected to sustain this
extra effort for a period of time. The demonstration of this fact had led
early in our work to the introduction of the time element into the test.
The principle involved is not a new one. It is merely the application of
a very old and well known one to the work of testing for optical fatigue.
If, for example, a sensitive test is wanted for the detection of fatigue in
a muscle, as good results cannot be expected if the test requires only
momentary effort on the part of the muscle as would be attained if the
endurance of the muscle were taken into account. For our purpose,
therefore, the old acuity test has been made into an endurance test, in
which the fatigue or loss of functional efficiency of the eye is measured
by its power to sustain clear seeing for a period of time. As such it
should and does show a sensitivity for detecting fatigue far beyond what
can be attained by the older and more established test when it is used
for that purpose."
Il62 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
The discussion in the eighth paragraph of the influence of ex-
pectation or pre-knowledge on the part of the observer is also
absurdly misleading. The discussion is introduced by the sen-
tence "That is, in the application of the test as used by the authors
of the paper the observer is in full knowledge of all its details."
Obviously the reader is meant to infer from this statement that
the observer is put under some exaggerated or special condition
of pre-knowledge not proper to a well conducted experiment.
Later when pinned down to cases it develops that the critic is able
to name only two items of which the observer has knowledge,
namely, the test object and the fact that in the 3-minute records
it is always kept at the same distance after work as before. Why
it is necessary in order to have a properly standardized acuity
experiment to give the observer a knowledge of the test object
and to change the type of judgment from recognition to that of
a space threshold, the surest and most reproducible of the sense
judgments, has been discussed at length in our first and fourth
papers. The second point, it is obvious, can not be of the slightest
consequence. As a matter of fact the observer does not know
unless he is told that the distance of the test object is the same
after work as before. The experimenter knows this, but there is
absolutely nothing in the conduct of the experiment to tell the
observer that the distance of the test object has not been changed
in the 3 hours that have elapsed since the first record has been
taken. But even if he did know it had not been changed, the
knowledge could not have the slightest influence on his judgment
of when the space between the dot and the vertical line in the
letter i sinks below the threshold of discrimination, how often it
goes below the threshold, or how long it stays there ; for it drops
below the threshold not because of any change in the distance or
size of the test object or its parts, but because the eye is not able
to hold its adjustment for clear seeing. For a somewhat full dis-
cussion of the importance of the factor pre-knowledge in experi-
ments in physiological optics, of how it may be eliminated and
compensated for in accord with the best principles of experi-
mentation at the present time, the reader is referred to Note 1, of
the paper "Some Experiments on the Eye with Inverted Reflec-
tors, etc.," which appears on previous pages of this number of
the Transactions.
EXPERIMENTS ON THE EYE H63
Up to this time in Dr. Cobb's discussion I had understood that
his doubts as to whether the results of our test have really meas-
ured the loss of efficiency, rested on several contentions : the fact
that only one other investigator had published results on the tests
besides ourselves ; his claim that no data has been published that
could be considered as showing a safeguarding of the results
against the influence of extraneous, factors; the charge that the
observer knows what the test object is and that it is the same
distance from the eye in the records taken before and after work ;
the recrimination that such precision as was attained by our
observers in the course of several months of training in one
feature of the experiment could not in the opinion of the ex-
perts of his acquaintance be obtained in a few minutes ; etc., etc.
In the ninth paragraph, however, it develops that :
In making reference to the possibility of the test being subject to
influences other than the state of efficiency or fatigue of the eye, the fact
in mind was that in the greater part of the work reported, the tests were
conducted with the observer at the same point and under the same light-
ing conditions as during the work period. That is to say, that in this
portion of the work the test was not conducted under the same conditions
in any two different experiments whose results are compared.
Dr. Cobb's contention here is that the 3-minute record before
and after the reading period should have been taken in a sepa-
rate test room having always the same intensity and distribution
of light regardless of what distribution and intensity of light
the eye was exposed to during the 3 hours of reading which
intervened. That is, immediately at the close of this period the
observer would have been brought into a room for the 3-minute
record in which for a part of the work the distribution effects
would have had to be widely different from the previous 3-
hours exposure (the distribution series), and for another part
of the work both the distribution and intensity would have been
widely different (the intensity series). Thus the eye in every
test would have taken the record at the close of work in a dif-
ferent state of adaptation or sensitivity than at the beginning.
How very futile and inadvisable this would have been more es-
pecially for the work in the intensity series I scarcely need
once more to point out. Even in the work in the distribution
series, the only part of the work for which Dr. Cobb's proposal
1 164 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
could have at all been considered, very great care would have
had to be exercised to see that the separate room was always
illuminated with exactly the same intensity of light that was
used in the room in which the reading was done. If the illumi-
nation of the two rooms were not accurately the same, a period
of adaptation would have had to be allowed before the 3-minute
record could have been made, which in case of the record taken
after work, would have given the eye opportunity to recover
from the fatigue induced by the work. It is obvious that a great
deal of difficulty would be encountered in accurately maintaining
this control; and if it were not so maintained an error of con-
siderable consequence would be introduced into the work. More-
over, in getting this control, not only the illumination of the test
card must be taken into account, but the brightness of the whole
field of vision with its complex distribution of light and shade,
for this conditions the state of adaptation of the paracentral
and peripheral portions of the retina, which in turn exerts an
influence on the part of the retina that receives the image of the
test object. It is obvious further that this duplication of light
and shade could not be made in a separate test room without
copying the work room and the lighting system employed in each
case, which would of course no longer make of it a separate
room. Furthermore, it was found early in the work that the
effects of smaller differences in lighting could be detected when
both the 3-minute records and the work were done under the
lighting conditions to be tested. That is, the total test procedure,
which includes both the 3-minute records and the reading, is
more sensitive when it is all done under the conditions to be
tested, than when a part of it is done under these conditions and
a part of it in a separate room. Since the method is more sensi-
tive when the whole procedure is conducted under the lighting
conditions to be tested, we can see no reason why even the purist
should demand that a part of it should be done under the condi-
tions to be tested and a part of it elsewhere so long as the results
are recognized to be the consequence of the 3-minute records
and of the reading. There are, it is obvious, two reasons why
the method should be more sensitive when the 3-minute records
are taken in the work room. ( 1 ) The method is more amenable
to control when the eye is subjected to no change in lighting
EXPERIMENTS ON THE EYE 1 165
effects in the 3 hours intervening between the two records
that have to be compared. And (2) the 3-minute record itself
is a task for the eye as well as the reading. The difference be-
tween the fatigue it induces in case of the first and second records
may be greater under a bad lighting system than under a good.
If so, this adds on to the effect of the reading to make up the
total effect determined by comparing the two records. Whether
it does or not, however, seems to me of little consequence for
it is differential of conditions just as well as the reading. That
is, if the effect does add on to the effect of reading, the total
result is only as if a longer reading period were used. Here,
however, Dr. Cobb files his final demurrer (footnote 5) : "There
would be no objection to the inclusion of this effect in the result
if there were in practical life any work that the eyes are called
upon to do at all comparable with the effect that such a test de-
mands." Our reply to this would be ( 1 ) that there are no tests
for acuity, momentary or sustained, comparable in effect with the
ordinary use of the eyes for the same length of time. If there
were they would not be tests; (2) the effect added is not the
total of the strain of the 3-minute record, merely the difference
in effect of two, one taken before and one after work; and (3)
if an effect is added, the net result is only the same as would be
attained if a longer reading period were used.
Dr. Cobb goes on to say that "More than this from the infor-
mation at hand I can not see that the intention of the authors
to conduct the test under conditions identical with those of the
work period was fulfilled." He bears this out with a descrip-
tion of the observer's position during the 3-minute records and
the reading period, as he interprets it. In the treatment of this
point Dr. Cobb's discussion indicates his viewpoint. Apparently
it was supposed that the observer sat primly erect with eyes
modestly lowered ("at an angle of about 450") away from the
garish effects of the selected products of modern lighting, tak-
ing great care to face these products to which it was the sole pur-
pose of the experiment to expose the eyes only so long as was
necessary to view the test object for the 3-minute records. Such,
he contends, is the natural inference from an inspection of Figs.
2, 3 and 4 (which show nothing but the test object, the track
on which it was carried and the observer's empty chair), and
Il66 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
"from what is said further in this note" describing the observer's
position, the details of which he fails to give or to reconcile in
the slightest regard with his interpretation. I may be pardoned
perhaps for pointing out that Dr. Cobb's inference is the natural
one on only two assumptions: (a) that he has not carefully read
the description of conditions given in the note in question; and
(b) that he has taken for granted that the authors have not a
sufficient comprehension of what they are trying to accomplish
in these tests and of the chief point of significance of the some-
what extensive results they have obtained. Allow me to quote
from the description given in the present paper.
Care was taken to have the eyes sustain as nearly as was possible the
same general relations to the objects of the room as were sustained when
the 3-minute records were taken. This could be done either by hold-
ing the head erect, etc., or by tilting slightly backward in the swivel chair
used by the observer and allowing the head to relax a compensating
amount. So far as the direct optical effects are concerned it would seem
to be immaterial which of these positions is chosen, so long as approxi-
mately the same field of vision is obtained. The latter is usually pre-
ferred by the observer as causing less general fatigue. When taking this
position, the book is elevated and held at approximately an angle of 450
(a little nearer to* the vertical than this perhaps).
Moreover, the description given in the third paper, while not
quite so full as this, differed from it in no way that could lead to
Dr. Cobb's interpretation, either as a necessary or a probable
criticism. But Dr. Cobb protests finally (footnote 4) : "This
position can not be comfortable." It is not so comfortable for
the eyes as the one we were naturally inferred by him to take,
but otherwise it is very comfortable indeed. For further proof
we can only recommend that he try it. The above description of
the reading position of the observer should also render pointless
the contention made in the latter part of footnote 5. This con-
tention is :
The objection to the standardization of the test conditions raised
by the authors further on, namely, that slight differences in the level of
adaptation will materially affect the results, applies with equal force to
the procedure of the authors as indicated by what I have just said. The
necessity emphasized for the control of the whole field of vision with its
complex distribution of light and shade applies equally well as an objec-
tion to the change in the distribution of light on the retina brought about
by shifting the eyes from the oblique reading position to the horizontal
EXPERIMENTS ON THE EYE 1167
position demanded by the test. The statement (note 4) that "Care was
taken to have the eyes sustain as nearly as possible the same general rela-
tions to the objects of the room ..." contains nothing to imply that
such a shift was avoided.
As we have already clearly shown by quoting from the original
description of conditions, the reading position was not oblique,
hence no shift from such a position to the horizontal is demanded
in passing from reading to the 3-minute record. Moreover, that
there shall be no abrupt transition from reading page to test card
a fixed interval of pre-exposure to a surface of the same bright-
ness and size of the test card is allowed before the 3-minute
record is begun.
The footnotes appended to Dr. Cobb's discussion are, I under-
stand, meant to apply specifically to our present paper. All of
them have already been covered in connection with the above
rejoinder but 2 and 3. Footnote 2 is based on a confusion arising
from Dr. Cobb not reading correctly our statement of the
standard of precision that must be attained in the practise on the
3-minute records before the observer was allowed to enter on the
next stage of the preliminary work. The 1 per cent, is not a
mean or average variation. It is an outside limit beyond which
no individual variation ever went for the observers whose results
were published in the paper. It is somewhat difficult to under-
stand how he could have misread the original statement. This
statement is : "For a single series of five tests these variations
in the time seen clear in the 3-minute periods have always fallen
within 1 per cent, for all of the observers we have used and for
all systems of lighting" (Trans. Aug. 30, 1915, p. 461). A typ-
ical mean variation in the time seen clear in one of these practise
series of five tests is for Observer R approximately 0.37 per cent. ;
for Observer G it was slightly smaller. Corresponding to the
mean variation in the time seen clear of 0.37 per cent, for Ob-
server R, the mean variation of the ratio time clear to time
blurred is 1.4 per cent. We hope this additional explanation will
clear up the doubt in Dr. Cobb's mind with regard to how the
mean variation was obtained for Table IX of the present paper.
In Table IX the mean variation was of the drop in ratio time
clear to time blurred produced by making a change in the con-
dition to be tested. This mean variation was taken of the drop
Il68 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
so that the average value of the drop could be compared with its
average variation to see whether the change produced by chang-
ing the system could be considered as significant. The citation
given by Dr. Cobb should not have caused confusion because it
was not only clear but obvious from the text just what was done
in both cases.
In the brief first statement made of our standard of precision
in the practise work on the 3-minute record, it was, we may say,
considered more significant for the purpose for which the 3-
minute record was to be used in the actual work of testing to
show that all of the individual variations fell within a given small
limit than to indicate what the average variations were, leaving
the reader in doubt as to how wide a range of throw the in-
dividual variations might have. As to whether the result was
expressed in terms of the time seen clear or the ratio time clear
to time blurred seems to me quite immaterial. Both expressions
are significant, and one is readily derivable from the other when
the time seen clear and the total time of observation are known.
In footnote 3 Dr. Cobb raises again the question already much
discussed of the possibility of introducing an objective check on
the influence of subjective factors. We have patiently explained
several times before that there are two ways of checking up the
influence of subjective factors, — the objective check and a care-
ful determination of the mean variation, and that neither one of
these possibilities has been overlooked in our work. We tried
for several months to devise a means of changing the test ob-
ject in such a way that an objective check could be had on the
registration of the observer without sacrificing the principle of
the test. Such a change of sufficient magnitude to be of any
definite service could not, we found, be made in the test object
which did not at the same time permit the eye to relax its strain
at the instant of change, which, it is obvious, destroys the very
feature which gives the test its superior sensitivity. The attempt
to get an objective check was made, I may say, to offset possible
criticism rather than because of any belief that it was necessary
for the purpose for which the test has so far been used ; for, as
we have already stated, a determination of both the maximum
and mean variations for the 3-minute records, each one of which
EXPERIMENTS ON THE EYE I169
consists of a number of separate judgments, had shown us that
the influence of expectation and other subjective factors has
been, under the conditions for which the work has been done,
of negligible consequence. Dr. Cobb suggests as an objective
check that different cards be used in some of which the space
between the dot and the vertical line of the letter i be obliterated
in different amounts by a fine pen. ' We have found the change
he suggests not to be of any additional service for the following
reasons: (i) A change that would be large enough to affect
appreciably the amount of time that the angle of separation be-
tween dot and line is below the threshold of discrimination is
too large to escape the observation of the observer. When the
eye goes out of adjustment, the lapse is apparently too abrupt
and too great to permit of a change that would not be detectable
to the observer with a well adjusted eye to influence significantly
the course of the record. That is, a diminution by so small an
amount would not put it below the threshold when the eye was
well adjusted, nor would an increase by the same amount put
it above the threshold in one of the lapses of adjustment. The
additional strain, moreover, does not seem to be significantly
great. It might be perhaps if the angle of separation which it is
necessary to employ were at or very near the threshold of dis-
crimination, but it is not at or very near the threshold of dis-
crimination, as we have explained many times. (2) The check
proposed is not directly objective, it could serve only indirectly
as a check and very indirectly at that. A test object like the
letter E, for example, which could be turned in different direc-
tions and the observer be required to tell which way it points is
used in acuity tests as an objective check. Here the judgment of
the observer is checked up directly by the knowledge of the ex-
perimenter. Dr. Cobb, however, proposes to vary the results
of the observer by varying one of the factors which is supposed
to influence these results, and from the working of this variation
to detect whether the observer is judging his experiences hon-
estly. This in experimental procedure is known as the method
of concomitant variations, and by common acceptance must itself
be very carefully checked up before its results are considered of
any significance. The only way it could be checked up would be
carefully to determine the mean variation for each change and
I I/O TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
compare this variation with the variation produced by changing
the angle of separation. This would have to be done before it
could be told whether the change was operative and thus even
the slightest check be had on the verity of the observer's judg-
ments. That is, in this roundabout procedure one would have
to rely fundamentally at every step on the check we have used
from the beginning, namely, a careful determination of the mean
variation, and the procedure itself invites cumulation of error
and uncertainty. Dr. Cobb's proposal is, in methodological pro-
cedure, not unlike setting a thief to catch a thief, and is to say
the least distinctly meretricious.
burrows: small incandescent lamps 1171
SMALL INCANDESCENT LAMPS AND SPECIAL
ILLUMINATION PROBLEMS.*
BY ROBERT P. BURROWS.
Synopsis: The paper presents certain improvements in miniature
lamps resulting in their increased use in commercial, professional, and
industrial fields; a brief study of dry cells and their relation to small
incandescent lamps in the various fields together with a suggested method
of testing dry cells in order to obtain such data as will enable the proper
application of small lamps; and a few interesting examples of how the
application of engineering knowledge to comparatively simple devices will
increase their usefulness. A few of the many uses of small lamps are
also mentioned.
The purpose of this paper is to call attention to the fact that the
small incandescent lamps commonly classed as miniature lamps
are coming to be recognized as contributing a great deal to certain
special fields of lighting. Not long ago small lamps were looked
upon as playthings and had little or no commercial application.
This was due, partly, to the limitations of the carbon filament in
applications where the cost of supplying energy is necessarily
high. With the introduction of tungsten as a filament material,
a considerably higher efficiency for these lamps was possible.
However, it was not until the introduction of the drawn-wire,
tungsten filament that the lamps became recognized as having
many commercial possibilities. This filament improvement, with
its increased efficiency and strength, did more than anything else
to place miniature lamps in the position they now hold. High
efficiency made possible the use of dry cells as a source of energy.
With the discovery that drawn-wire tungsten could be coiled
into concentrated filaments, further fields for miniature lamps
were opened. Certain problems in the projection of light were
materially simplified by the concentrated filament and because it
was possible to get a greater length of wire in a small space, the
high voltage, small bulb lamps of very much increased efficiency
* A paper presented at the ninth annual convention of the Illuminating Engineer-
ing Society, Washington, D. C, September 20-23, I01 5-
The Illuminating Engineering Society is not responsible for the statements or
opinions advanced by contributors.
1 172 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
found their use in decorative fields. The introduction of an inert
gas into certain types of these small lamps greatly increased their
efficiency.
Following the increased demand came a study of the manufac-
ture of these miniature lamps, a study which is constantly going
on, and which is gradually taking them out of the class of hand
made products. The difficulties encountered in cutting and
mounting by hand a little piece of wire one third the diameter of
a human hair and, say, 10 mm. in length can be more readily
appreciated when it is known that 0.5 mm. in the length of fila-
ment in certain types of these lamps means about 5 per cent,
difference in voltage. Thus it can be seen how a higher quality
and comparatively low cost is obtainable with machine manu-
facture. A number of these miniature lamps now have their
filaments coiled and cut by very accurate machines and a few have
semi-automatically mounted filaments.
With the growing interest in miniature lamps came greater
demands for their correct application to the fields involved.
Where a few years ago almost any lamp which would give light
would suffice, it is now demanded that light not only shall be
produced economically, but that every detail of the lamp must
be specially designed for the purpose. For instance, the dry
cell hand-lantern first came on to the market with demands that
all the light possible should be obtained from a single dry cell
without regard for the life of lamp or battery. These lanterns
have now settled down to replace the old oil lantern, and the
manufacturers are requiring that the life of battery and lamp
shall receive fully as much consideration as the light produced.
In order to obtain a maximum amount of light throughout the
life of a dry cell it became necessary to study their limitations.
This involved study of current limitations, recuperation, the effect
of heat, cold and dampness, and the ageing of cells while not in
actual use.
Inasmuch as dry cells are coming to be used as the source of
energy for small lamps in a great many fields, it will undoubtedly
be of interest to study some of their characteristics.
One of the first questions that presented itself in this study was
how to obtain data which would place all of the limiting char-
burrows: small incandescent lamps i 173
acteristics of dry cell operation on such a basis that the results
would be comparable at all times. The Electro-chemical Society
had at one time published a few suggestions on the subject, but
as far as could be determined, nothing standard had been decided
upon. After a number of tests under various conditions the
following procedure was drafted and sent to the various large
battery manufacturers with a request for their suggestions and
criticisms and received their approval.
METHOD OF TESTING DRY CELLS WHEN DISCHARGING
THROUGH MINIATURE TUNGSTEN LAMPS.
Class No. 1 — Flashlight Batteries.
Class No. 2 — Standard No. 6 Dry Cell Batteries.
General Instructions.
1 — All tests are to be conducted at a temperature of not lower than 700 F.
and as near thereto as possible. Actual temperature to be noted.
2 — The current at rated volts is to be obtained on each lamp before start
of test.
3 — All lamps and tests are to be numbered.
4 — At the completion of each test potential-time curves are to be plotted
for all the data obtained. Besides the four curves obtained from
the data taken on tests of standard No. 6 dry cell batteries, a curve
is to be plotted which will be the average of the above four curves.
In comparison tests the same scale is to be used for all curves.
5 — The open circuit or recuperating periods are to be not less than two
hours and shall be a fixed period of time for each test. The last
period each day as well as the last period each week-end is to be
noted.
6 — Enough extra lamps of the same rating are to be on hand for each
test in order to replace lamps immediately, should any burn out.
7 — The voltmeter used is to have an electrical resistance of approximately
100 ohms per volt and to be in circuit only when readings are taken.
8 — The electrical resistance of the wires between lamps and batteries must
not exceed 0.0025 ohm per cell. (This is approximately the resist-
ance of 1 foot of No. 14 B-S gauge copper wire.)
Class No. 1 — Flashlight Batteries.
The battery cells shall be soldered together by means of copper wires
in order to insure good connections between cells.
The following data should be obtained :
1 — Initial open circuit voltage at start of test only.
2 — Initial closed circuit voltage at start of test only.
1 174 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
3 — The voltage at the end of the ist, 3rd and 7th periods of burning. The
voltage at the end of every 7th period thereafter.
Each period is to be of five minutes duration, with four periods per
day.
The life of the battery is to be considered ended when the potential
drops to 0.5 volt per cell.
In plotting curves, time shall be stated in minutes.
Class No. 2 — Standard No 6 Dry Cell Batteries.
The following data should be obtained :
1 — Initial open circuit voltage at start of test only.
2 — Voltage readings during the ist, 3rd and 5th periods of burning and
during every 5th period thereafter.
There shall be four periods per day.
The duration of each period shall be as follows :
Duration of period
Less than 0.3 watt per cell 1 hour
0.3 to 0.5 watt (inclusive) per cell 30 minutes
0.5 to 1.3 watts (inclusive) per cell 15 minutes
1.3 watts or more per cell 5 minutes
The following voltage readings are to be taken:
Duration of period Readings
I hour initial closed circuit
End of 20 minutes
End of 40 minutes
End of period
30 minutes initial closed circuit
End of 10 minutes
End of 20 minutes
End of period
15 minutes initial closed circuit
End of 5 minutes
End of 10 minutes
End of period
5 minutes initial closed circuit
End of 1 minute
End of 3 minutes
End of period
The life of the battery is to be considered ended when the potential
of each cell drops to 0.7 volt.
In plotting curves time shall be stated in hours.
A typical discharge curve of two dry cells in series plotted from
data taken in accordance with the above outline is shown in Fig. 1 .
The average curve is plotted as the average of the points on the
1 This reading to be taken after needle has come to apparent rest.
burrows: small incandescent lamps
1 175
other three curves and is the curve for which lamps must be de-
signed to operate most efficiently. It must be understood that this
curve is actually a series of cycles of discharges and recuperations.
The start and completion of such a cyclic curve is shown in Fig. 2
and was obtained by means of a recording voltmeter with a special
scale. It is interesting to note the difference between these cycles
as shown in Fig. 3. These particular curves show the difference
between the first and fourth cycle and bring out the point that
initial closed circuit readings are of little value. Fig. 4 shows a
1
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Fig. 1.— Typical voltage discharge curve of dry cells.
(Three batteries ; two dry cells in series.)
Fig. 2. — Chart of voltage variation of dry cells at
start and completion of discharge.
cycle at the end of the life of the two cells shown in Fig. 1 and
shows why it is not economical to use these cells after their
potential has dropped to 0.7 volt per cell. It will be noted that
the voltage starts at 2.2 volts and drops in one minute to 1.4 volts
which is only 50 per cent, voltage of the battery and would con-
sequently give little light. The curve continues on down to 0.2
volt, and this cycle will be repeated for several hours, but the
abscissa in hours would continually decrease, thereby shortening
the period of efficient light production to a matter of seconds. It
1 176 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
has been shown by numerous tests that after two hours recuper-
ation of the cell there is no appreciable increase in power. Fig. 12
curve A, shows the marked effect of low temperature. This
curve was obtained from a test of five cells in series operating at a
temperature of about 22 ° F. After twenty hours the battery was
placed in a temperature of about 700 F. and, as curve B shows, it
increased in voltage while discharging until it nearly reached the
normal operating voltage for that period in its life. It has been
stated that a drop of 50 in temperature below 700 decreases the
17
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Fig. 3. — Voltage variation between first and fourth periods of discharge.
A, variation in first period ; B, variation in fourth period.
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Fig. 4. — Cyclic variation of voltage for one period of discharge and recuperation.
Two dry cells in series ; variation during one complete period.
current by one ampere. However, this does not reduce the
capacity of the battery if the latter is brought back to a tempera-
ture of 700 F., as shown by the previous curve. It will be seen
that the two curves in Fig. 12 do not quite come together after the
cold battery had been brought up to the temperature of the one
operating under normal conditions. This may be explained by
the fact that this battery was subjected to a certain amount of
moisture. Moisture permanently reduces the capacity of a cell.
burrows: small incandescent lamps i 177
There are a great many uses for small lamps using dry cells as
a source of energy, chief among which is the dry cell hand
lantern. A number of different types of these lanterns are shown
in Fig. 5. Lamps of this type are used by watchmen, campers,
firemen and farmers.
The reflector design for hand lanterns has become quite im-
portant. At first the manufacturers wanted all the light possible
in one direction and consequently used a polished parabolic re-
flector which was practically useless for any other purpose than
to see comparatively great distances ahead. This did very well
for watchmen, or hunters and campers, but was almost useless
around the home or on the farm. Reflectors are now being scien-
tifically designed to meet the demand for a more distributed light.
Another use for dry cell lighting coming into prominence is the
lighting of summer cottages or permanent camps where a great
deal of light is not needed. The convenience of having a little
light is considered well worth the small expense of such an in-
stallation.
An interesting example of what can be accomplished by apply-
ing a little engineering knowledge to a comparatively simple, but
nevertheless ingenious device, is that of an egg tester recently
equipped with miniature lamps and proper reflectors. The orig-
inal model of this device was equipped with one 6- volt, 0.84
ampere miniature lamp, using four No. 6 dry cells as a source of
energy and having a piece of tin as a reflector (Figs. 9 and 9a).
Two small parabolic reflectors were designed and recommended
to be placed one behind each opening and to contain 6-volt, 0.35
ampere lamps. These reflectors and the distribution obtained are
shown in Figs. 8 and 8a. It will be seen that the maximum light
is directed through the egg and not to one side. As a direct result
of these recommendations, the battery life was increased 400 per
cent., the effective light flux was increased 300 per cent., and the
number of eggs candled per battery increased 400 per cent.
Among other novelties using flashlight lamps are a fishing
bobber, shown in Fig. 6; luminous fish bait, where a small lamp
with a dry cell as a source of energy is placed in the "tail" of the
bait, for night or early morning fishing. In the industrial field a
good example of the use of these small lamps is an office signal
1 178 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
system (Fig. 10), not in wide use, but of great convenience.
This system is so arranged with small lamps that the executive
may place a call for any of his assistants and know by the signal
on his desk whether or not his call is receiving attention.
In the professional field there are a great many uses for these
small lamps. The retinascope, a small instrument for throwing
an intense beam of light into the pupil of the eye, using a dry cell
as a source of energy, is coming into use among doctors for eye
examination. There are numerous other small devices on this
same principle, such as a cycstoscope for internal diagnosis,
dentists' mouth mirrors with a lamp and battery attached to the
handle, and various devices for eye, ear and nose examination
where, under usual conditions, proper seeing is difficult.
The class of lamps commonly known as automobile lamps and
their application to automobile lighting is so well-known that it
is hardly necessary to discuss them here. These same lamps,
however, are being used for motor boat lighting and in some cases
utilize the same sources of power as are used on automobiles. A
very simple and effective method of lighting motor boats is with
dry cells. A battery of twelve dry cells connected in series-multi-
ple to obtain an average voltage of 3.5 volts, is used as a source
of energy and has such a capacity that it is possible with care,
to use the port and starboard lights, two riding lights and thirteen
cabin, galley and stateroom lamps with one set of batteries per
season. For this purpose 3.5-volt, 0.42-ampere lamps operating
at an efficiency of 1.25 w. p. c. are used. A complete outfit is
shown in Fig. 7.
Probably the best example of exacting conditions imposed upon
these small lamps now as compared to the consideration given
them a few years ago is that of the miner's lamp. This subject
has previously been discussed before this society so that great
detail is not necessary. The conditions imposed upon the lamp
were that they should have a uniform life of 200 or 300 hours
depending upon the source of energy, not more than 5 per cent,
giving a life less than 250 or 170 hours, respectively. The second
condition imposed was that at no time during the life of the lamp
and a twelve-hour discharge of the battery should the amount of
)\-}&
Fig. 5.— Typical dry cell hand lanterns.
Fig. 6.— Fishing bobber. Fig. 7.— Motor boat lighting equipment.
85° 75° 65° 55° 45" 35°
Fig. S. — Suggested reflectors
for egg tester.
Fig. Sa.
90° 75°G5°55"45° 35° 2S
Fig. 9.
Fig. 9a.
Fig. io.- — An office signal system.
burrows: small incandescent lamps
1 179
light fall below 1.5 lumens. The third condition imposed was
that the uniformity of current and candlepower should meet
fairly close conditions. To meet these meant careful reflector
design and study of the battery discharge curves so that the most
efficient lamp would be designed for this service.
The first step in this design was to obtain an average potential-
time-discharge curve for a number of batteries discharging
through lamps of such current rating that they would discharge
the battery to its most economical voltage in the allotted time.
Such a typical curve (A) is shown in Fig. n. By means of an
exponential equation involving lamp life with applied voltage,
curve C, Fig. 11, was plotted. From this curve it is possible to
ascertain the life of a lamp when burned at any voltage on
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Fig. 11. — Typical voltage discharge of
miner's lamp battery.
Fig. 12. — Effect of low temperature on voltage
discharge of dry cells.
curve A. For example, if a lamp is designed for 300 hours life
at 2 volts, in order to determine its life at 1.9 volts, it is only
necessary to find 1.9 volts on curve A and the corresponding point
on curve C. This gives a correction factor which when multiplied
by 300 will give the life at 1.9 volts. The average ordinate D of
this curve gives the voltage V for which a lamp may be designed
to have the same life as when burned on the potential-time curve
A. The obtaining of this voltage is most important since the life
of incandescent lamps is an inverse function of voltage.
Inasmuch as the requirements were so drawn up as to combine
the reflector with the lamp, it was necessary to take up the ques-
tion of reflector design. The reflector engineers were held to the
angle of the beam of light, and also the distribution across the
Il80 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
beam. Fig. 14 shows the theoretical minimum allowable distri-
bution of illumination on a plain surface 20 in. (0.58 m.) from a
reflector as required by the Bureau of Mines. From this distri-
bution, it was a comparatively simple matter to plot a curve show-
ing the distribution of light from a reflector which would give
this distribution of illumination. This curve is shown in Fig. 13.
From this curve it was necessary to obtain the shape of the re-
flector which would give the required distribution of illumination
kM^^aH^^^^-
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Fig. 13. — Distribution curve of mine lamp reflector to meet
Bureau of Mines specifications.
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Fig. 14. — Minimum distribution of illumination to meet Bureau
of Mines specifications for miner's lamps. (Theoretical dis-
tribution across a 7-ft. circle.)
over the circle specified. In Fig. 15 is shown one shape of re-
flector which will give a distribution closely approximating that
required. The finish of the reflector must give an illuminated
area which will answer the requirements that when "observed2
with the eye there shall be no black spots within the 7-foot circle
or any sharply contrasting areas of bright and faint illumination
2 Procedure for establishing a list of permissible Portable Electric Mine Lamps.
Schedule 6A, Dept. of Interior, Bureau of Mines.
burrows: small incandescent lamps
1181
anywhere." Two finishes have been used, porcelain enamel and
aluminum. With a knowledge of the efficiency of these finishes
and the volume of light required from a reflector, the amount of
light the lamp would have to give was determined, including
factors of safety, since the foregoing are minimum values. After
determining this amount of light, and transferring it into a value
of candlepower, the final step was to combine this candlepower
with the voltage and current before determined and to obtain the
efficiency of the lamp. This efficiency had to be such as to give
the required life. With the above data, it was possible to design
lamps to give the maximum amount of light under the conditions
laid down.
All the foregoing details are mentioned to show that in small
lamps a careful study of voltage conditions, reflector design, and
+m
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Fig. 15. — Experimental mine lamp reflector.
the requirements of the device using these small lamps is becoming
more necessary as the uses of these lamps increase. Opposed to
the old idea that small lamps were mere playthings is the growing
tendency to expect them to do even more than should be expected
from them. Uniformity of performance, as judged from ex-
perience with large lamps, is very difficult to obtain, for small
lamps are generally of low voltage and high current. The ac-
curacy of manufacture nesessarily is not as good and the diffi-
culty in supplying the proper voltage at the lamp terminals is
great. The regulation of the sources of energy used is not the
best and each small voltage drop in wires or contacts is a con-
siderable percentage of the total. Also, for the same efficiency,
the life is only one tenth to one third of that of the large lamps,
Il82 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
and on account of the types of bases used the allowable current
is limited. A careful consideration of these small lamps will
show that they should receive at least as much attention as the
large lamps where they are to be applied to important fields of
illumination.
DISCUSSION
Mr. L. C. Porter: The number of uses to which min-
iature lamps are being put is almost infinite and almost every day
sees new devices and new ways of using them. It is a very wide
field and one which is rapidly increasing. The lamps are used
for all sorts of spectacular efforts, in theatrical work especially,
and since the beginning of the European War there has been
a great demand for miniature lamps for hand lanterns used
in the trenches. A number of interesting applications have been
brought about by this war. Small lamps are used for signaling
and a large number of these signal outfits are being sold. The
lamps and reflectors are held in hand and used for signal purposes
both at night and day.
Stereopticon and small moving picture machines for home use
is another field for the lamps. The railroads are using a consid-
erable number for position light signals; the medical and dental
professions use large quantities. In fact, the miniature lamp
business is growing more rapidly than that of regular lamps.
CODE OF LIGHTING H&3
CODE OF LIGHTING.
Below is a prefatory note which was omitted from the Code of
Lighting that appeared in the November 20, 191 5, Vol. X, No. 8,
issue of the Transactions, beginning on page 605.
The Code, which was prepared jointly by the Committee on
Factory Lighting and the Committee on Lighting Legislation,
was presented at the Ninth Annual Convention held in Wash-
ington, D. C, Sept. 20-23, 1915. The Code has been accepted
by the Council and is issued in separate pamphlet form by the
Society.
PREFACE.
The following Code of Lighting for Factories, Mills and other
Work Places, has been prepared by committees of the Illumin-
ating Engineering Society in order to make available authoritative
information for legislative bodies, factory boards, public service
commissions and others who are interested in enactments, rules
and regulations for better lighting.
While the code is intended as an aid to industrial commissions
and other similar bodies in those states and municipalities which
shall actively take up the questions of legislation as related to
factory and mill lighting, it is intended in equal measure for the
industries themselves as a practical working guide in individual
efforts to improve lighting conditions. The language of the code
has not been drafted according to legal phraseology but is simple
and pointed throughout, thus being readily available for trans-
forming into legal orders, and at the same time as a working
guide in practical design and installation work.
1 184 TRANSACTIONS OE ILLUMINATING ENGINEERING SOCIETY
REPORT OF THE CHAIRMAN OF THE COMMITTEE
ON LIGHTING LEGISLATION.*
During the early part of the past year the Committee on
Lighting Legislation made a general survey of the state laws
relating to lighting in the United States and prepared a trans-
cript (taken from the statute books) of the laws relating to
lighting in the states of New York, Pennsylvania, Connecticut,
Illinois and Wisconsin.
The study of these laws led to the conclusion that with few
exceptions existing state lighting legislation is crude, fragmen-
tary and often meaningless.
It was suggested that this committee frame a model lighting
law to serve as a guide to legislators contemplating the enact-
ment or amendement of laws pertaining to lighting. The diffi-
culties in the way of framing a model law applicable to all classes
of lighting are apparent and the committee decided to confine its
work for the present to formulating a code of lighting for fac-
tories, mills and other places and a code of lighting for school
houses.
Accordingly a special committee on factory lighting and a
special committee on school lighting submitted to the Committee
on Lighting Legislation technical data and rules upon which to
base a lighting code.
A large part of the attention of the Committee on Lighting
Legislation has been devoted for the past six months to the con-
sideration of a comprehensive report of the Factory Lighting
Committee, of which Prof. C. E. Clewell is chairman, containing
material upon which was based the Code of Lighting now placed
before you.
The purpose of the code is primarily to provide legislators
with material upon which to base laws, rules and regulations re-
lating to the lighting of factories, mills and other work places,
but the Code is intended also to serve as a guide to factory man-
agers and others in remodeling the lighting of existing buildings
and in planning the lighting of new buildings.
Although much of the material offered is concrete and directly
serviceable in the design of lighting installations, the Articles are
* Read at the convention of the Society at Washington, D. C, Sept. 20, 1915.
COMMITTEE ON LIGHTING LEGISLATION I185
necessarily more or less general depending upon the limitations
imposed by the present state of the art of lighting.
The committees have had the advantage not only of construc-
tive criticism from their own combined membership of fifteen,
including a legal representative skilled in legislatve work, but
also from a considerable number of industrialists and factory
managers connected with some of the leading manufacturing
companies and institutions in the country.
The Code is to be published in separate pamphlet form with
cover and is to have an index which is now being prepared.
Committee on Lighting Legislation.
L. B. Marks, Chairman,
O. H. Basquin,
C. O. Bond,
C. E. Clewell,
O. H. Fogg,
C. L. Law,
M. Luckiesh,
F. J. Miller,
G. H. Stickney,
L. A. Tanzer,
W. H. Tolman.
Committee on Factory Lighting.
C. E. ClEwell, Chairman,
W. A. D. Evans,
T. J. Litle, Jr.,
D. M. Petty,
R. E. Simpson.
Il86 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
ERRATUM.
The accompanying table of data was inadvertently omitted
from the paper entitled "Present Practise in the Lighting of
Armories and Gymnasiums with Tungsten Filament Lamps," by
A. L. Powell and A. B. Oday, which appeared in the November
20, 1915, issue (vol., No. 8, pp. 746-759) of the Transactions.
(Note.— This table is to aament Lamps," by A. L. Powell and A. B.
ONS.)
EQUIPMENT.
Regiment
Infantry—
7th X. G. X. V
ist X.G. X. V
Location
New York
Citv
New York
City
Di^.rrange-
siment of
in lamps
taggered
5 rows
Legularly
n 3 rows
Height of
lamps in
feet
Side
rows 40
Centre
Balcony
19 ft. -wide. 25-w., round bulb. Fig. 1
all frosted lamps. In white
bowl refls. Set flush with
ceiling. 10-ft. centers.
On side walls under and above Fig. 2
balcony. Bracket fixtures on
16' centers. Prismatic en-
closing elobes. Two 25-watt
n«t
Il86 TRANSACTIONS OF ILLUMINATING ENGINEERING SOCIETY
ERRATUM.
The accompanying table of data was inadvertently omitted
from the paper entitled "Present Practise in the Lighting of
Armories and Gymnasiums with Tungsten Filament Lamps," by
A. L. Powell and A. B. Oday, which appeared in the November
20, 1915, issue (vol., No. 8, pp. 746-759) of the Transactions.
ERRATA.
Page 1 151. — Text; third line from bottom, omit word "observa-
tion."
Page 1 1 58. — Seventh line from top; substitute the words "the
comparison" for "it."
Page 1 1 58. — Delete late sentence of the first paragraph.
Page 1 158. — Second paragraph, ninth line; words, 'is nothing
more or less than a space threshold' should be 'is nothing
more or less than the judgment of a space threshold.'
Page 1 165. — Delete the second sentence reading, 'In the treat-
ment of this point Dr. Cobb's discussion indicates his view-
point.'
Page 1 165. — Line 21, words 'have not a sufficient comprehen-
sion,' should be 'have only a minimum comprehension.'
Page 1 1 68. — Fourteenth line from bottom word 'observation'
should be 'notice.'
[The sentences deleted above were not the author's.]
(Note.— This table is to aament Lamps," by A. L. Powell and A. B.
ONS.)
EQUIPMENT.
Regiment
Infantry —
7th N. G. X. V.
71st X. G. X. V.
•SahX.G.X.Y.
i2thX. G. X.Y.
ist X. G. X. J.
47th X. G.X. Y.
small shed .
23rd X.G. X.Y.
State Armory
State Armory
Coast Defence—
X. G. X. Y.
Location
DiA-rrange-
siknent of
in [ lamps
[86
155
New York
Citv
New York
City
New York
City
New York 200
City
Xewark. 25?
X. J.
taggered
5 rows
egularly
n 3 rows
taggered
5 rows
Regularly
3 rows
Legularly
4 rows
Height of
lamps in
feet
Side
rows 40
Centre
row 45
Balcony
19 ft. wide. 25-w., round bulb. Fig. 1
all frosted lamps. In white
bowl refls. Set flush with
ceiling. 10-ft. centers.
On side walls under and above Fig. 2
balcony. Bracket fixtures on
16' centers. Prismatic en-
closing globes. Two 25-watt
each globe.
:i ft. wide. Below 200-watt
lamps. Prismatic bowl re
flectors on 34-ft. centers.
Gas below and above balcony
for emergency.
Balcony narrow.
Brooklyn 130 daggered ]
3 rows
Brooklyn
Schenectady
X. Y.
Legularly j
3 rows ]
130 Regularly
3 rows
Albanv, ix^
x. y.
Xew York
City
180
taggered . Outside 20
5 rows Center 25
egularly
2 rows
Xo balconv.
rius ini)U- 1
to .ceo,,,,, am . ,,,,,,, e„ti,l,,l •■ !•„,,„, Practise i„ the ■,.,„!„« of Armorle. and Gymnasiums with Tungrten HI, ,,t Ump. ■■ bv A I, Powell aid A B
<M»y,wM<* ■•'• ■'•"'PP. 746-759 of vol. X, No. 8 (November ao, 19.5) toue of the Transactions.) P *
API
SNDIX 1
lira
NATIC
n Dai
'A ON
Armories Lighted with Various Types 01
Modern
Equipment.
lafcJt
«i, ft
Heigli
1 oloi
ol
Color
of
Color
of
!:I';!s
Size <>|
Total
Watt*
Type of R< Bei toi
Type
Fixture
w
Height of
feet
Balcony
Aetna
Com
ti ■;
G.N. V.
|B6 x 17I
51.000
90
(,reen
Gr en
Ught
28
as
28.000
0.55
0.<j2
Prl maU. i nclofltnc mm i i,„
l'"wl rrll.vtur witli n. I...I |.m
iii.ilimli-.li „va mouth. 17" (tin
m " high 1
Steel
Bide
rows 40
Centre
all frosted lamps in whifa
bowl refls, Set flu-.h will
row 45
ceiling. io-fl
■
>
SO
Brick
Gray
«gj
24
500 b. f
12,000
o.5o
0.73
Pn ltd in ismatic bowl red*.
1 1' i" dia ■
6- spread
■~°
On side walls under and
■
j-.i
closing globes. Two
each globe.
Brick.
- . ,t 1 1» v-
Gray
Med.
48
loo b. f
19,200
0.50
0.72
■' ■' i" i unati bowl refls.
difl
2 light ring
fixtures
■ '
■
25
It ft. wide. Below 2cowat
lamps. Prismatic tiowl re
flectorson 34-ft. a a
Utfc N
City
JOOX.So
36.00°
50
Dark
Dark
Dark
36
300 b. f
10,800
0.30
o-43
Pn ■—• .] prismatic bowl refls
n'-"di.i.. 7 W" high.'
fixtures
1
:°
Gas below and above 1
for emergency.
60
Buir
Buff
32
cSr
12.800
o,37
o.4l
la" Sat white gloss reflector.
1 ombina-
:
20
Balcony narrow.
47th N
1 -bed
Brooklyn
26.000
40
Blue
lurk
1,0am*
8
75o
6,000
0.23
0.36
1 nt'1'i-.ing globes. 12
dia. witb ventilated holder.1
Stcel
■
32
cable
- G.N.Y
Brooklyn
2OOX30O
60,000
7S
Cream
Oak
Med.
■5
b'.T
15,000
0.25
0.42
opal red. 16
dia., .," .Ii 1 p. nmmil Mjeki t am
Sir. 1
1
35
State Armory
Schenectady,
N V
130 I 85
11,000
-
"
-
•8
icob. f
,,*»
0.44
0.40
Pn ssed prismatic bowl refl., s,\
deep.o
firtu™
I 1 ■_'iil:irly
-
-.rmory
X. V.
MO* 175
42,000
15
Cream
Pine
Dark
26
, i- :;,
.9,500
0.46
0.7.
10" enameled stei '■ 1
it inclosing globe.1
fi££
-
Outside 20
Center 25
City
1S0 x 170
30.500
70
White
MgW
8
K
8,000
0.36
0.44
enti ocloaing globe
■ :.i [at 1 copper 1 isiii]
around socket. 30" over all.«
Steel
cable
35
No balcony.
vth X. G. N. V
Xew York
City
40,000
..,,
I Mil
!.
14
270o°bdf.
14,500
0,28
0-43
Deep bowl porcelain enamele<
eflectors 17" dia."
Steel
fci mil.irly
40
200-watt under balcony will
prismatic reflectors.
ij,thN.f,. NY.
Brooklyn
s„
;;:;:;
16
16
750 b. f.
b. f.
28,000
0-43
0.69
Deep bowl dense opal red., if>'
il socket am
skeleton holder.6
Steel
1
Side
rows a
■;'fW i -
work
rows 60
- -- N. V .
45
Dark
dark'
': ■ .
24
0.30
0.43
16" enameled steel refl., ventilat
Steel
'
City
ed bolder and 8"
2nd Batterv.
globe around lamp.10
- S. Y . .
Xew York
City
50
Dark
Dark
27
clear
13.500
0.2S
0.40
- enameled steel red., ventilat
ed bi 'i li t and opali a en
Stei :
■ ■'
3*
3rd Battery,
globe around lamp.1"
N. Y.
Brooklyn
,,,,,.
Nat.
lllack
">-5S
1 pal refl., iff
Steel
: .
tan
b 1
. ep, mogul socket and
Cavalry—
bark
'
Squadron A .
New York
Cily
50
Buff
Tan
l..irk
8
cS
'
0.27
0.39
S" enameled steel refl., ventilat-
ed holder and B" opalescent
globe around lamp.1"
Steel
I-:, -ularly
30
Brooklyn
54.0OO
70
White
30
0.42
0.6s
1 dense opal refl., 16"
.;. . |> mogul socket ami
skeleton 1
Steel
35
1 J !
Engines*
loam
■
Cily
70
Brick
tight
Rrct-ii
Pin.
2,
b. f.
21,000
0.31
Deep bowl porcelain enameled
sleel red., r difl
Steel
legularly
43
Ha Icon v 14 ft. wide, [■:■' ft
high.
aulcor,* .
Brooklyn
var-
,1..!
5
0.36
Deep bowl dense opal refl.. 16'
Stei 1
"5
Pig. 4
.rowii
oak
wood
. 1 1 _ 1 . ■ ' <l> L-p, inogul socket am!
skeleton bolder.5
cable
rical
2nd N-
Clak,
Pine
50 b, f.
0.45
Deep bowl dense opal refl., 16'
,lj,i . .., .I. i']i. miimil siiil.i. 1 ;mh
skeleton holder.''
■
work
I
.ex**
40,000
70
Brick
Dark
wood
18
e-icTr
.S,ooo
o.45
o.75
■," enameled Bteel refl and 1 1
split rical enclosing globe.11
Steel
staggered
.-, rows
45
Fig. 5
■ d
Toffiv
tll'il Of
the- ol
ler pra
:tise th
following data are appended.)
200 x 300
6O.OO0
85
Tan
Wood
Wood
730
40
28,800
0.48
0.46
1 Corona combination gna and
■ 1 : : 1 j
tllll-iih '.
electric fixtures: 15 K'<s ■""' ■■'
center 30
electric each.
■
Brooklyn
51.OOO
85
CreAtn
Blue
Wood
900
clfar
36,000
0.70
0.67
1 Corona combination .gas and
electric fixtures: 15 gas and 30
electric each.
_
Regularly
3 rows
1
TRANSACTIONS
OF THE
Illuminating
Engineering Society
NO. I, 1915
PART II
Miscellaneous Notes
TRANSACTIONS I. E. S. - PART II
Council Notes.
A meeting of the Council was held
January 14 in the general offices of the
Society, 29 West 39th Street, New York,
N. Y. Those present were: A. S.
McAllister, president; E. M. Alger.
C. O. Bond, H. Calvert, Ward Harrison.
George A. Hoadley, C. A. Littlefield,
general secretary; L. B. Marks, Preston
S. Millar, A. S. Miller, J. Arnold Nor-
cross, A. L. Powell, representing G. H.
Stickney, vice-president and chairman
of the Committee on papers. Upon invi-
tation: M. Luckiesh, chairman of the
School Lighting Committee; A. Hertz,
chairman of the Finance Committee ;
and Norman Macbeth, chairman of the
New York Section.
The Finance Committee submitted an
oral report on the total expenses and
receipts for the first three months of
the present fiscal year compared with
the corresponding period of the last
year. Upon recommendation of the
committee the Council authorized the
payment of vouchers No. 1943 to No.
1976 inclusive, aggregating $1,919.91.
A written progress report was re-
ceived from the Time and Place Com-
mittee (1915 Convention). The report
indicated that of the places under con-
sideration, Washington, D. C. was the
one most favored.
An oral report was given by Ward
Harrison on behalf of Mr. W. M. Skiff,
chairman of the 1914 Convention Com-
mittee.
Reports on section activities were re-
ceived from F. A. Vaughn, vice-presi-
dent of the Chicago Section; A. L.
Powell for G. H. Stickney, vice-presi-
dent of the New York Section; Ward
Harrison, vice-president of the Pitts-
burgh Section; and George A. Hoadley.
vice-president of the Philadelphia Sec-
tion.
Mr. C. O. Bond reported orally on
a proposal that the Philadelphia Section
become affiliated, along with the local
sections of other engineering societies,
with the Engineers' Society of Phila-
delphia. It was resolved that, if the
Philadelphia Section desires to join the
movement, the Council will be disposed
to consider the proposal favorably, pro-
vided the expense is not too great.
Mr. M. Luckiesh gave an oral report
on behalf of the Committee on School
Lighting and submitted the manuscript
of a lecture entitled, "Safe-Guarding
the Eyesight of Children." It was re-
solved that, after the manuscript had
passed through the usual publication
channels, the lecture be published; and
that the committee announce the fact
that the lecture is to be available for
those interested in the subject of school
lighting.
A written report was received from
the Committee on Glare from Reflecting
Surfaces, giving data on the results of
tests made on the so-called "window"
envelopes. It was voted that the report
be returned to the committee with a
request that the last paragraph be re-
vised as indicated, and that the title be
so worded as to indicate that these en-
velopes had passed through the mails
and were submitted for test by a letter
carriers' association.
The appointment of the following
Committee on Remodeling the Lighting
of the General Offices was confirmed :
H. E. Ives, chairman; Clarence L. Law.
Thos. W. Scofield; L. B. Marks and
George W. Cassidy, advisory members.
A written report was received from
the Committee on Remodeling the Light-
ing of the General Offices. It was
TRANSACTIONS I. E. S.— PART II
voted that the Committee be requested
to proceed with a temporary installation,
as outlined in the committee"s report,, in
order that it may be tried out by the
Council at its meetings.
The following additional committee
appointments were confirmed :
Committee on Factory Lighting : C. E.
Clewell, chairman ; W. A. D. Evans,
T. J. Litle, Jr., R. E. Simpson and G.
H. Stickney.
Committee on Popular Lectures: C. F.
Scott.
Committee on Constitutional Revision :
W. D. Weaver, chairman ; Louis Bell,
L. B. Marks, and C. H. Sharp.
The resignation of the following
committee members were accepted with
regret :
Dr. H. E. Ives from the Committees
on Research, Popular Lectures, and
Lighting Legislation. Dr. Alexander
Duane from the Committee on Papers.
An invitation from the trustees and
faculty of the University of North
Carolina to appoint a representative to
attend the inauguration of Mr. William
Kidder Graham as president of the
university was received. President
McAllister was empowered to appoint
a representative.
A proposal to create a class of mem-
bers to be known as fellows was tabled
for the next meeting of the Council.
It was understood that copies of this
proposal would be mailed to the mem-
bers of Council for consideration in the
meantime.
The following communication was re-
ceived from Dr. C. H. Sharp, secre-
tary of the United States National Com-
mittee of the International Commission
on Illumination.
In the normal course of events this com-
mittee would be obliged at this time of the year
to request from the Illuminating Engineering
Society the regular annual contribution of $100
toward the expenses of the committee and toward
the payment required by the International Com-
mission on Illumination. Last year the com-
mission was supported by the contributions of
five countries, namely England, France, Ger-
many, Italy and United States. The expenses
of the commission were very small so that the
honorary secretary has a substantial fund in the
treasury, which on account of the temporary
suspension of the activities of the commission is
likely to be but little encroached upon. This
committee, therefore, makes no call on you at
this time for any further funds. The expecta-
tion is, however, that at the close of the war the
International Commission on Illumination will
again become active and the regular contribu-
tion will be required.
The following resolution submitted
by the Committee on Editing and Pub-
lication was adopted :
The Committee on Editing and Publication
recommends that technical and trade journals
be advised that the papers of the Society
may be reprinted in whole or in part, subse-
quent to the dates of presentation, by any
member of the technical or trade press, pro-
vided proper credit is given.
It was suggested by several members
of the Council that all matters of routine
business might be transacted by the
Council Executive Committee previous
to each council meeting.
Consideration of the outlines of work
for the present year, submitted by com-
mittees, was deferred until the next
meeting.
Section Activities.
CHICAGO SECTION
Prof. Morgan Brooks of the Univer-
sity of Illinois delivered a lecture on
"Vision and Illumination" at a meeting
of the Chicago Section in the rooms of
the Western Society of Engineers,
December 18, 1914. During his lecture
Prof. Brooks described an instrument
which he called a rapid illuminometer.
At a meeting held January 29, Dr.
Clayton H. Sharp presented a paper
TRANSACTIONS I. E. S. — PART II
entitled "The Knowns and Unknowns of
Physical Light."
The tentative program of papers for
the Chicago Section for the season 1914-
1915 is as follows :
February — Other Light Sources (Gas
and Electric).
March — Decoration : Color Schemes ;
Fixture Forms ; Use of Colored Sources.
April — Lighting of Small Interiors :
Homes ; Small Offices ; Show Windows.
May — Lighting of Large Interiors :
Churches ; Halls ; Large Offices.
June — Lighting of Open Air Spaces :
Streets ; Building Exteriors : Signs.
NEW ENGLAND SECTION
A meeting of the New England Sec-
tion was held in the Engineers' Club on
Friday, February 5. Mr. Munroe
Rhodes Pevear of Boston gave a paper
on "Three Color Illumination" which
was illustrated by practical demonstra-
tions. Mr. Pevear has made an exhaus-
tive study of commercial methods for
procuring light of any degree, intensity
or color. The paper was accompanied
by a number of demonstrations.
The programs of coming meetings
will be announced later.
PHILADELPHIA SECTION
A meeting of the Philadelphia Section
was held January 15 at the Engineers'
Club, 1317 Spruce Street. Two papers
were presented, one by Harry Markle
on "The Lighting of Willow Grove
Park," and the other on "Piping Houses
for Gas Lighting" by Mr. H. R. Sterrett.
Seventy-five members and guests were
present.
The following program has been an-
nounced for the rest of the season :
February 8 — Joint meeting with Amer-
ican Institute of Electrical Engineers.
"A Year's Progiess in Illumination" by
Prof. Geo. A. Hoadley; "Recent Devel-
opments and Applications of Incandes-
cent Lamps" by Geo. H. Stickney. Elec-
tric lamps will be exhibited.
February 19 — "Scientific Management"
by Frederick W. Taylor. A demonstra-
tion of the pathescope, a new moving
picture device, will be given.
March 19 — "A Method of Securini:
Uniformity of Reading of the Flicker
Photometer with Different Observers"
by Herbert E. Ives and E. F. Kingsbury.
Photometric apparatus will be exhibited.
April 16 — "The Problem of Lighting
Design," by Prof. Arthur J. Rowland.
This paper will include a discussion of the
following items : Methods used for de-
signing: (a) direct lighting (b) indirect
lighting ; difficulties and faults in the use
of such methods ; accuracy to be ex-
pected in the results accomplished ; what
constitutes good design. Exhibition of
new types of lighting fixtures.
May 21 — "Store Lighting" by W. R.
Moulton. This meeting will be held in
Baltimore. Md. The place will be
announced later.
NEW YORK SKCTION
The New York Section held a joint
meeting with the Metropolitan Section
of the Professional Photographers'
Society of New York in the Engineer-
ing Societies Building, January 14. Two
papers were presented : one "The Appli-
cation of the Tungsten Lamp to Pho-
tography" by Mr. M. Luckiesh, physicist
of Nela Research Laboratory, Cleve-
land, O. ; the other "Gas Lamps for
Photography" by Mr. R. F. Pierce of
the Welsbach Company. Gloucester,
N. J. The papers were discussed by
representatives of both societies. Mr.
J. E. Williamson gave a short talk on
"Submarine Photography," which was
accompanied by lantern slides.
The tentative program for the New
TRANSACTIONS I. E. S. — PART II
York Section for the rest of the season
is as follows :
February — "The Type C Lamp for
Street Lighting" by Mr. W. H. Rolin-
son; "The Magnetite Lamp for Street
Lighting" by Mr. C. A. B. Halvorson, Jr.
March — This meeting is to be ar-
ranged by the Fine Arts Committee of
the Section. There will be a symposium
on light by various artists, decorators
and architects ; each speaker is to have
about ten minutes to explain the light-
ing needs of his profession.
April — Joint meeting of the New York
sections of the Illuminating Engineering
Society, the National Commercial Gas
Association and the National Electric
Light Association to discuss the com-
mercial side of the good lighting propa-
ganda. Addresses will be given by rep-
resentatives of the three organizations.
May — To be announced later.
June — Dr. Hollis Godfrey of Phila-
delphia, Pa., has been invited to present
a paper on "Good Lighting as an Aid to
Welfare Work" to include a description
of the work which he has done in the
Metropolitan Life Insurance Building in
New York.
PITTSBURGH SECTION
The Pittsburgh Section held a joint
meeting with several engineering socie-
ties in Cleveland, O., January 29. A
popular lecture entitled "Safeguarding
the Eyes of School Children," accom-
panied by a series of lantern slides, was
given by Mr. M. Luckiesh.
The program, as far as known, for
the rest of the season is given below.
February 19 — A popular lecture on
"Home Lighting."
March 19 — Joint meeting with the
American Institute of Electrical Engi-
neers. Paper: "Projector Lanterns and
Searchlights" or "Incandescent Lamp
Manufacture."
New Members
The following twenty-four applicants
were elected members of the Society at
a Council meeting held January 14 :
Adam, John Neil
New Business Assistant to Division
Agent, Public Service Electric Co.,
271 North Broad St.. Elizabeth,
N.J.
Andrews, William S.
Consulting Engineering Department,
General Electric Co., Schenectady.
N. Y.
Butler, Henry E.
Assistant to Illuminating Engineer,
General Electric Co., Illuminating
Engineering Laboratory, Schenec-
tady, N. Y.
Billau, Lewis S.
Assistant Electrical Engineer, Bal-
timore & Ohio Railway Co., Balti-
more, Md.
Rmkrson, Harrington
Counseling Engineer on Efficiency,
The Emerson Co., 30 Church St.,
New York, N. Y.
Emerson Guy C.
Consulting Engineer for Municipal
Works. Boston Finance Commis-
sion, 73 Bemont St., Boston, Mass.
Faught, Ray C.
Local Supply Department (Mana-
ger) General Electric Co., 121 7
Munsey Building, Baltimore, Md.
Huilman, D. B.
Electrical and Mechanical Engineer,
Philadelphia & Reading Railway
Co., Reading, Pa.
Hoover, John Walter.
Supt. Lighting and Merchandise
Sales, Gas Division, Consolidated
Gas, Electric Light & Power Co.
of Baltimore, Baltimore, Md.
TRANSACTIONS I. E. S. — PART II
Hess, Wm. L.
Doctor, eye, ear, nose and throat,
400 California Building. Denver.
Colo.
Hewitt. Conrad
Supt. of the Building, Metropolitan
Museum of Art, Fifth Avenue and
82nd St.. New York. N. Y.
Jones, W. R.
Engineer of Construction. Univer-
sity of Penna. (Light & Heat Sta-
tion). 3401 Spruce St.. Philadelphia.
Pa.
Kingsbury, Edwin F.
Laboratory Assistant. Physical Lab-
oratory, United Gas Improvement
Co., 3101 Passyunk Avenue, Phila-
delphia. Pa.
Mohr, William
Supt. of Lamps and Lighting. Muni-
cipal Department, Room 8. City
Hall, Baltimore, Md.
McLaughlin. John C.
Chief Clerk. Potomac Elec. Power
Co., 231 Fourteenth N. W.. Wash-
ington. D. C.
Marsh, George Everett
Assistant Professor of Electrical
Engineering, Armour Institute of
Technology, Chicago, 111.
Muncy, Victor Emanuel
Professor of Mechanics and Applied
Electricity, Ohio Mechanics' Insti-
tute. Cincinnati. Ohio.
Orner, Aleert
Designer and Salesman of Lighting
Fixtures, Consolidated Chandelier
Co., 132 West 14th St.. New York.
N. Y.
Pillsbury, Charles L.
Consulting Engineer 895 Metropoli-
tan Life Building. Minneapolis.
Minn.
Pfeiffer, Bernard V.
Engineer, Nashville Gas & Heating
Co.. 611 Church St.. Nashville.
Tenn.
Platt, Charles J.. Jr.
General Foreman, United Electric
Light & Power Co., 130 East 15th
St., New York. N. Y.
Rosenfeld, Eugene I.
President & General Manager, Eu-
gene I. Rosenfeld & Co., Inc., 8 S.
Howard St., Baltimore, Md.
Simonson, G. Metcalfe
Assistant Electrical Engineer, State
Department of Engineering, Forum
Building, Sacramento, Cal.
Wilder, Stuart
Engineer, Electrical Dept, West-
chester Lighting Co.. 1st Avenue
and 1st St.. Mt. Vernon, N. Y.
Index for Volume IX.
The index for Volume IX (1914
Transactions) is mailed with this issue.
NOTICE.
The Committee on Editing and Pub-
lication will be glad to publish in the
Transactions personals, obituaries, and
such news items as are of interest to
the members of the Society. All items
of this sort should be addressed to the
Illuminating Engineering Society, 29
West 39th Street, New York. N. Y.
TRANSACTIONS
OF THE
Illuminating
Engineering Society
NO. 2, 1915
PART II
Miscellaneous Notes
TRANSACTIONS I. E. S. — PART II
Council Notes.
A meeting of the Council was held
February n in the general offices of
the Society, 29 West 39th Street, New
York, N. Y. Those present were :
A. S. McAllister, president; E. M.
Alger, C. O. Bond, H. Calvert, P. W.
Cobb, Ward Harrison, C. A. Littlefield.
general secretary ; L. B. Marks, treas-
urer; Preston S. Millar, Alten S. Miller,
W. Cullen Morris, J. Arnold Norcross,
G. H. Stickney. Upon invitation Mr.
V. R. Lansingh.
Written reports on section activities
were submitted by the following vice-
presidents: Ward Harrison (Pittsburgh
Section) ; George A. Hoadley (Phila-
delphia Section) ; G. H. Stickney (New
York Section) ; and F. A. Vaughn
(Chicago Section).
After a discussion of whether the
Philadelphia Section of the I. E. S.
should become an affiliated member of
the Engineers' Society of Philadelphia,
it was voted that the matter be laid
upon the table.
Upon recommendation of the Finance
Committee, the Council authorized the
payment of vouchers Nos. 1977 to 2006
inclusive and Nos. 2008 to 201 1 inclusive
aggregating $1,050.01.
It was voted that the report of the
Committee on Glare on window en-
velopes be published in the Transac-
tions subject to the usual publication
procedure of the proper committees.
Mr. Preston S. Millar, chairman,
reported orally for the Sustaining Mem-
bership Committee.
A written report of the Committee on
Time and Place was read by Mr. G. H.
Stickney, chairman. The committee
recommended that the 1915 Convention
be held in Washington, D. C, during
the third or fourth week in September.
Committee appointments and changes:
The resignation of Mr. Preston S.
Millar from the Committee on Consti-
tutional Revision was accepted.
The resignation of Mr. G. H. Stick-
ney from the Committee on Factory
Lighting was accepted.
The resignation of Dr. H. E. Ives as
chairman of the Committee on Remod-
eling the Lighting of the General Offices
was accepted with a vote of thanks
from the Council.
Dr. C. H. Sharp was appointed sec-
retary of the Committee on Constitu-
tional Revision.
Prof. W. S. Franklin was appointed a
member of the Committee on Popular
Lectures.
Mr. H. Calvert submitted blue prints
showing by curves the expenses and
income of the Society from 1907 to 1914.
It was voted that the Committee on
Constitutional Revision be requested to
recommend (1) changes in the Consti-
tution which would increase the dues
of members to $10.00 and create an
additional grade of members having
dues of $5.00; (2) qualifications for
membership in these two grades.
Section Activities.
CHICAGO SECTION
Nelson M. Blank. M. D., of Milwau-
kee, Wis., delivered a lecture on "A
Resume of the Physical, Physiological
and Psychical Phases of Vision," at a
meeting of the Chicago Section in the
rooms of the Western Society of Engi-
neers, February 25, 1915-
The tentative program of papers for
the Chicago Section for the season 1914-
191 5 is as follows:
March — Decoration : Color Schemes ;
Fixture Forms ; Use of Colored Sources.
April — Lighting of Small Interiors:
Homes; Small Offices; Show Windows.
TRANSACTIONS I. E. S. — PART II
May — Lighting of Large Interiors :
Churches ; Halls ; Large Offices.
June — Lighting of Open Air Spaces :
Streets; Building Exteriors; Signs.
NEW ENGLAND SECTION
A meeting of the New England Sec-
tion was held in the Engineers' Club,
Boston, February 26. Three papers
were presented : "Effects of Radiation
on the Eye" by Dr. Louis Bell, "The
Axial Chromatic Aberration of the
Human Eye" by Dr. P. G. Nutting, and
"How Faulty Illumination Injures the
Eye" by Dr. Walter B. Lancaster.
The programs of coming meetings will
be announced later.
NEW YORK SECTION
A meeting of the New York Section
was held in the Engineering Societies
Building, February 11. Mr. C. A. B.
Halvorson presented a paper on "The
Arc — Its Status as a Street Illuminant,"
which was accompanied by a demonstra-
tion of the effect of varying current and
voltage at the arc, and a description of
the possibilities of the various types of
metallic flame arcs.
The tentative program for the New
York Section for the rest of the season
is as follows :
March — A paper by L. C. Porter and
W. G. Gove on the lighting of the new
cars of the New York Municipal Rail-
way Corporation.
April — Joint meeting of the New
York Section of the Illuminating Engi-
neering Society, the National Commer-
cial Gas Association, and the National
Electric Light Association to discuss the
commercial side of the good lighting
propaganda.
May — To be announced later.
June — To be announced later.
PHILADELPHIA SECTION
The Philadelphia Section held a joint
meeting with the American Institute of
Electrical Engineers at the Engineers'
Club, on February 8. Two papers were
presented, one by George A. Hoadley
on "A Year's Progress in Illumination,"
and the other on "Recent Develop-
ments and Applications of Incandescent
Lamps" by George H. Stickney.
A meeting of the Philadelphia Section
was held February 19 at the Engineers'
Club, 1317 Spruce Street.' Mr. Fred-
erick W. Taylor presented a paper on
"Scientific Management." A demon-
stration of the pathescope, a new mov-
ing picture device, was given.
The following program has been
announced for the rest of the season :
March 19 — "A Method of Securing
Uniformity of Reading of the Flicker
Photometer with Different Observers"
by Herbert E. Ives and E. F. Kingsbury.
Photometric apparatus will be exhibited.
April 16 — "The Problem of Lighting
Design," by Prof. Arthur J. Rowland.
This paper will include a discussion of
the following items : Methods used for
designing: (a) direct lighting, (b) indi-
rect lighting; difficulties and faults in
the use of such methods ; accuracy to be
expected in the results accomplished;
what constitutes good design. Exhibi-
tion of new types of lighting fixtures.
May 21 — "Store Lighting" by W. R.
Moulton. This meeting will be held in
Baltimore, Md. The place will be
announced later.
PITTSBURGH SECTION
The Pittsburgh Section held a meet-
ing in Cleveland on January 29 at the
Addison School, 79th and Hough
Streets. Preceding the meeting an
informal dinner was held at the Univer-
sity Club, following which there was
TRANSACTIONS I. E. S. — PART II
an inspection of several rooms in the
Addison School, each of which was
equipped with a different system of
lighting fixtures. Two papers were
presented, one, "Safeguarding the Eye-
sight of School Children," accompanied
by a number of slides, was presented
by Mr. Magdsick in the absence of the
author, Mr. M. Luckiesh; and the other,
"A Discussion of Present Practise in
School Lighting" by Mr. E. B. Rowe.
Interesting examples of school room
lighting were shown by slides. Sixty
members and guests, including members
of the Board of Public Education and
teachers, were present. This meeting
indicates a broadening of the activities
of the Society and represents an attempt
to popularize good lighting through
public education. The Section's efforts
are directed toward the saving of eye-
sight, and no better place for this work
is apparent than in the schools. Par-
ticular credit is due the authors of the
papers for preparing good material, for
their time and expense in preparing
slides and illustrations, and for arrang-
ing the several different displays in the
school rooms. The co-operation of the
local Board of Education and the school
authorities was given freely and appre-
ciated.
The regular monthly meeting of the
Pittsburgh Section, held February 19
at the Engineers' Society Auditorium,
was preceded by a dinner at the Fort
Pitt Hotel. Before the meeting the
members and guests inspected several
exhibition booths showing various light-
ing features. In a preliminary talk,
Dr. Edward Stieren described by means
of colored charts the structure of the
human eye and its usual optical defects.
Prof. Francis C. Caldwell of the Ohio
State University presented a paper
entitled "Illumination and Eye Fatigue."
His subject included a general resume
of the methods used in measuring visual
acuity, and a discussion of the results
of the various investigators.
March 19 — Joint meeting with the
American Institute of Electrical Engi-
neers. Paper: "Projector Lanterns and
Searchlights" or "Incandescent Lamp
Manufacture."
New Members.
The following twenty-three applicants
were elected members of the Society at
a Council meeting held February 11:
Ache son, Albert R.
Professor of Mechanical Engineer-
ing, Syracuse University; Consult-
ing Engineer, Bureau of Gas and
Electricity, City of Syracuse; Syra-
cuse, N. Y.
Ball, Wm. J.
Secretary, Tri-City Electric Com-
pany, 1529 Third Ave., Moline, 111.
Blakeslee, Doraf Wilmot
Assistant Professor of Electrical
Engineering, University of Arkan-
sas, Fayetteville, Ark.
Carpenter, C. A.
Electrical Engineer, Graham, Burn-
ham & Co., 1417 Railway Exchange,
Chicago, 111.
Fleming, John P.
New Business Representative, The
United Gas Improvement Co., 1035
Market St., Philadelphia, Pa.
Goldsmith, Lester M.
Testing and Designing Engineer,
Perpetual Fuse Company, 1606 S.
Fourth St., Philadelphia, Pa.
Gleason, Marshall T.
Gleason, Tiebout Glass Co., 99 Com-
mercial St., Brooklyn, N. Y.
Gross, J. Harry
Park Engineer, Park Board, Druid
Hill Park, Baltimore, Md.
TRANSACTIONS I. E. S. — PART II
Howe, Lucien
Ophthalmologist, 520 Delaware Ave.,
Buffalo, N. Y.
Hirsch, H. H.
President, Hirsch Electric Mine
Lamp Company, 314 N. 12th St.,
Philadelphia, Pa.
Kelley. J. B.
Salesman, Frank H. Stewart Elec-
tric Co., 37 N. 7th St., Philadelphia,
Pa.
KOLLMORGEN, FREDERICK L. G.
Optical Expert, Keuffel & Esser Co.,
Adams St., Hoboken, N. J.
Lienesch, Walter H.
General Manager, Chicago Concrete
Post Co., 608 S. Dearborn St.,
Chicago, 111.
Lee, Stanton P.
Architect, 53 Third St., Troy, N. Y.
Norris, B. H.
Assistant to W. D'A. Ryan. General
Electric Co., Illuminating Engineer-
ing Laboratory, Schenectady, N. Y.
Porter, Geoffrey
Assistant Chief Engineer, B. C.
Electric Railway Co., Ltd., Canall
St., Vancouver, B. C.
Pindell, Wm. H.. Jr.
Incandescent Lamp Salesman, Ster-
ling Electric Lamp Division of Gen-
eral Electric Co., 313 Union Trust
Bldg., Baltimore, Md.
Ramirez, Charles E.
Representative, Bayley & Sons, Inc.,
101 Park Ave., New York, N. Y.
Seiler, Alvix
Agent for Westinghouse Lamp Co.,
Greensburg, Pa.
Sinclair, H. A.
Secretary and Treasurer, The
Tucker Elec. Construction Co., 114
W. 30th St., New York, N. Y.
Thompsox. Robt. J.
Manager. Welsbach Co.. 863 Mis-
sion St., San Francisco, Cal.
Tomlixsox, L. C.
Electrical Engineer, 32 Greenleaf
St., Maiden, Mass.
Wynne, V. C.
Consulting Engineer, 90 State St.,
Albany, N. Y.
Sustaining Membership.
The George Cutter Company of South
Bend. Ind., and the New Haven Gas
Light Company were elected sustaining
members of the Society at a Council
meeting held February 11.
Personals.
L. B. Marks and J. E. Woodwell, con-
sulting engineers, 103 Park Avenue,
New York City, announce that they Will
dissolve partnership on May 1, 1915-
Mr. Woodwell will locate his offices at
8 West 40th Street, where he will con-
tinue the general practise of consulting
engineer, and Mr. Marks will retain his
offices at 103 Park Avenue and will
specialize as heretofore in illuminating
engineering.
Dr. Henry Phelps Gage and Prof.
Simon Henry Gage are the authors of
a book entitled "Optic Projection" pub-
lished recently by the Comstock Publish-
ing Co.
Mr. Douglass Burnett was elected
chairman of the Commercial Section of
the N. E. L. A. at a meeting held in
Chicago, February 13.
Mr. Wilbur B. Foshay, formerly with
the Northwestern Electric Co., is now
president of the Washington Public
Service Co. of Portland, Ore.
TRANSACTIONS I. E. S.— PART II
Mr. H. Foster Boggis is secretary and
treasurer of the Boggis, Dietz Electric
Co. in Milwaukee, Wis.
Mr. E. B. Rowe, who in the last years
has held successively the positions of
resident engineer, assistant chief engi-
neer and chief illuminating engineer of
the Holophane Works, severed his con-
nections with that organization March I.
Mr. Rowe is now secretary and engineer
of the Enterprise Electric Construction
& Fixture Co., 6509 Euclid Avenue,
Cleveland, Ohio.
Back Numbers of the Transactions.
The Illuminating Engineering Society
is desirous of obtaining copies of the-
following issues of the Transactions :
1906 (Volume I) :
Nos. 1, 2, and 3.
1907 (Volume II) :
Nos. 1 and 2.
1914 (Volume IX) :
No. 7-
Members or others having copies of
these numbers which they wish to dis-
pose of should communicate with the
general office of the Society, 29 West
39th Street, New York, N. Y.
/
TRANSACTIONS
OF THE
Illuminating
Engineering Society
NO. 3, 1915
PART II
Miscellaneous Notes
TRANSACTIONS I. E. S. — PART II
Council Notes.
At a meeting of the Council held
March n, twenty-seven applicants were
elected members of the society. Their
names appear elsewhere in this issue of
the Transactions.
It was resolved that final action in
dropping delinquents who owe for 1913
and 1914 dues be deferred until the June
meeting.
Reports on section activities were
received from the following vice-presi-
dents : Mr. Ward Harrison for Pitts-
burgh ; Prof! George A. Hoadley for
Philadelphia; G. H. Stickney for New
York; and F. A. Vaughn for Chicago.
It was voted that the Council accept
the proposal of the Philadelphia Section
to affiliate with the Engineers' Society
of Philadelphia for the period of one
year, with the understanding that the
cost to the society will not exceed the
sum of $350.00.
Progress reports were received from
the following committees : Sustaining
Membership. Popular Lectures, School
Lighting, Remodeling the Lighting of
the General Offices, Exhibition Booth
(Gas), Exhibition Booth (Electric),
Membership, Constitutional Revision,
Lighting Legislation.
The following committee appoint-
ments were confirmed :
Mr. Douglass Burnett on the National
Membership Committee.
Mr. Clarence L. Law, chairman of
the Committee on Remodeling the Light-
ing of the General Offices.
Mr. E. S. Marlow, chairman of the
1915 Convention Committee.
The work of the 19 14 Convention
Committee being completed, it was voted
that the committee be discharged with
a hearty vote of thanks from the Coun-
cil and the Illuminating Engineering
Society for services rendered.
Those present at the meeting were :
A. S. McAllister, president; H. Calvert,
Ward Harrison, S. G. Hibben, George
A. Hoadley, C. A. Littlefield, general
secretary ; L. B. Marks, treasurer ;
Preston S. Millar, Alten S. Miller,
J. Arnold Norcross, G. H. Stickney.
Upon invitation, Mr. A. Hertz, chair-
man of the Finance Committee.
/
A meeting of the Council was held
April 8 in the general offices of the
Society, 29 West 39th Street, New York,
N. Y. Those present were : A. S.
McAllister, president; E. M. Alger,
C. O. Bond. H. Calvert, J. D. Israel,
C. A. Littlefield, general secretary ;
L. B. Marks, treasurer; Preston S.
Millar. Alten S. Miller, and J. Arnold
Norcross.
Mr. Preston S. Millar, chairman of
the Sustaining Membership Committee,
announced that the sustaining member-
ship dues of the Edison Lamp Works
of the General Electric Co.. Harrison,
N. J., had been raised upon request of
the member.
A written report on the Philadelphia
Section activities by Prof. George A.
Hoadley, vice-president, was read by
Mr. H. Calvert.
A written report was received from
the Committee on Membership. The
report showed that since October 1, 1914,
the additions to the membership totaled
117; the defections in the membership
during the same period totaled 97, leav-
ing a net gain of 20. The total indi-
vidual membership as of April 8 was
1.492.
TRANSACTIONS I. E. S. — PART II
A written report was received from
the chairman of the Committee on
Remodeling the Lighting of the General
Offices.
The committee was discharged with
thanks.
A written report containing a list of
proposed amendments to the Constitu-
tion was received from the Committee
on Constitutional Revision. The report
was also accompanied by a communica-
tion to the membership of the society
which the committee recommended be
sent out with the proposed amendments
in advance of the election.
The proposed amendments having
been received and considered favorably
by the Council, it was resolved that the
general secretary be instructed to send
out the aforementioned communication
and proposals previous to the forthcom-
ing annual election.
The Committee on Glare from Reflect-
ing Surfaces submitted two reports —
the second and third of a series to be
submitted by the committee — on the sub-
ject of "The Optical Properties of
Diffusing Media." One gave a classifi-
cation of diffusion, nomenclature and
the physical theory of diffusion; the
other dealt with instruments and meth-
ods for measuring diffusion and the
theory of diffusion photometry.
It was resolved that the reports of
this committee be put through the usual
channel of publication, as they become
available, and published in the Trans-
actions upon acceptance by the Com-
mittee on Papers.
Written reports were also received
from the Committees on Editing and
Publication, Reciprocal Relations with
other Societies, and Section Develop-
ment. Upon consideration of a recom-
mendation contained in the report of the
Committee on Editing and Publication —
that all Transactions cuts which are
more than three years old be sold as
junk — it was ordered that all line cuts
which have been used in the Transac-
tions prior to the first of January of
this year be destroyed, but all half-tones
be retained.
The Committee on Lighting Legisla-
tion submitted a report stating that it
had considered (i) a report containing
material for formulating a code on fac-
tory lighting, which had been received
from the Committee on Factory Light-
ing; (2) a report submitted by the Com-
mittee on School Lighting containing
material upon which it is proposed to
base a code on school lighting; and
returned both reports to the respective
committees with suggestions for revi-
sion.
The appointment of Mr. M. Luckiesh
to the Committee on Lighting Legisla-
tion was confirmed.
It was announced that the 1915 Con-
vention of the Society would be held at
the New Willard Hotel, Washington,
D. C, September 20-23 inclusive.
Communications were received from
Mr. F. A. Vaughn, delegate of the
I. E. S. to the Eleventh Annual Con-
vention of the Illinois Gas Association ;
W. A. Ferguson of the Commonwealth
Edison Company, in regard to holding
Council meetings outside the city of
New York ; and E. C. Jones, president
of the American Gas Institute, regard-
ing the convention of his organization
in San Francisco.
It was voted that Mr. C. O. Bond be
asked to make recommendations to the
president regarding the appointment of
TRANSACTIONS I. E. S. — PART II
two members of the I. E. S. to arrange
for the presentation of two papers — to
be credited to the I. E. S. — to be deliv-
ered at the San Francisco Convention
of the American Gas Institute ; and that
the president be empowered to appoint
such members.
It was suggested that a future meeting
of the Council be held in Philadelphia
or a city other than New York.
Section Activities.
Chicago Section.
Meetings.
March 25, 1915. Auditorium, Western
Society of Engineers, Monadnock Block.
Paper : "Color in Lighting," by M.
Luckiesh. Attendance 63.
The tentative program of papers for
the Chicago Section for the season 1914-
1915 is as follows :
April — Lighting of Small Interiors :
Homes ; Small Offices ; Show Windows.
May — Lighting of Large Interiors :
Churches ; Halls ; Large Offices.
June — Lighting of Open Air Spaces :
Streets; Building Exteriors; Signs.
New England Section.
Meetings.
March 26, 1915, Afternoon and Even-
ing. Engineers' Club, 2 Commonwealth
Ave., Boston, Mass. Papers presented
in the afternoon : ( 1 ) "Daylight Glass,"
by Dr. H. P. Gage; (2) "Artificial Day-
light," by R. B. Hussey; (3) "Semi-
Indirect Lighting by Gas," by R. F.
Pierce. Papers presented in the even-
ing: (1) "Determining Factors in Arti-
ficial Illumination Problems Primarily
as Related to Architecture and Decora-
tion," by D. Crownfield; (2) "Safe-
guarding the Eyesight of School Chil-
dren," by M. Luckiesh.
New York Section.
Meetings.
March II, 1915. Engineering Societies
Building. Paper : "A Practical Study
of Car Lighting Problems," by Messrs.
W. G. Gove and L. C. Porter. Mr. P. S.
Bailey gave a demonstration of four
different sizes of headlight lamps for
interurban and suburban cars. Mr.
G. H. Stickney demonstrated various
systems of interior car lighting by means
of a booth erected for this purpose.
Mr. W. P. Horn exhibited / new car
lighting reflector which has been sug-
gested for railway cars. Attendance 80.
April 19, 1915. Auditorium of the
Consolidated Gas Company's Building,
130 East 15th St. Joint meeting with
the National Electric Light Association
and the National Commercial Gas Asso-
ciation. Address by President Holton
H. Scott, of the N. E. L. A. Papers:
(1) "The Value of the Illuminating
Engineering Society to Commercial
Men." by Mr. Norman Macbeth ; (2)
"Illuminating Engineering as Applied to
the Business of the Gas Company," by
Mr. R. F. Pierce.
May — To be announced later.
Philadelphia Section.
Meetings.
March 19. 1915. Joint meeting with
Franklin Institute. Papers: (1) "Photo-
sculpturing," by Prof. J. Hammond
Smith, illustrated; (2) "On the Choice
of a Group of Observers for Hetero-
chromatic Measurements" ; (3) "Addi-
tional Experiments on Colored Absorb-
ing Solutions for Use in Heterochro-
matic Photometry" ; and (4) "A Method
of Correcting Abnormal Color Vision
and Its Application to Flicker Photom-
TRANSACTIONS I. E. S. — PART II
etry," by Dr. Herbert E. Ives and Mr.
E. F. Kingsbury. Attendance 50.
April 16, 1915. Drexel Institute, 32nd
and Chestnut Sts. Papers: (1) "The
Problems of Lighting Design," by Prof.
Arthur J. Rowland; (2) "Safeguarding
the Eyesight of School Children," by
M. Luckiesh.
The tentative program of papers for
the Philadelphia Section for the season
1915 is as follows :
May 21 — "Store Lighting," by W. R.
Moulton. This meeting will be held in
Baltimore, Md. The place will be
announced later.
Pittsburgh Section.
Meetings.
March 9, 1915. Joint meeting with the
local section of the American Institute
of Electrical Engineers. Papers: (1)
"The Manufacture of New Types of
Mazda Lamps," by Mr. R. E. Myers ;
(2) "The Use of Lenses in Signal
Work," by H. S. Hower. Interesting
exhibits illustrated both papers.
New Members.
The following twenty-seven applicants
were elected members of the society at
a meeting of the Council held March 11,
1915:
Arenberg, Albert L.
Sales Engineer, Central Electric
Co., 320 So. Fifth St., Chicago, 111.
Bell, W. B.
Public Service Electric Co., 188
Ellison St., Paterson, N. J.
Bull, John H.
Supervising Engineer, Ballinger &
Perrot, Marbridge Building, New
York, N. Y.
Cox, W. A.
Public Service Electric Co., Newark,
N.J.
Duvall, Benjamin A.
Sales Dept., The Consolidated Gas
Electric Light & Power Co., 100 W.
Lexington St., Baltimore, Md.
French, C. H.
Public Service Electric Co., 759
Broad St., Newark, N. J.
Gorge, S. V.
Electrical Contractor, 841 1 Eigh-
teenth Ave., Brooklyn, N. Y.
Harrison, Benjamin
Electrical Contractor, 65 11 Eigh-
teenth Ave., Brooklyn, N. Y.
Jones, W. L.
Manager, Fixture Dept., Electric
Construction & Machinery Co.,
Electric Bldg., Rock Island, 111.
Mayhew, Zenas D.
District Clerk, Edison Electric Il-
luminating Co. of Brooklyn, 360
Pearl St., Brooklyn, N. Y.
Owen, Charles D.
New Business Assistant to the
Division Agent, Public Service Elec-
tric Co., 118 Main St., Hackensack,
N.J.
Potter, N.
Public Service Gas Co., 188 Ellison
St., Paterson, N. J.
Perkins, M.
Public Service Gas Co., 418 Federal
St., Camden, N. J.
Ramsey, Harold E.
Assistant Electrical Engineer, Le-
high Coal & Navigation Co., Elec-
trical Dept., Lansford, Pa.
Schwartz, Frederick
Store Manager, Shapiro & Aronson,
20 Warren St., New York, N. Y.
Schwartz, H. M.
Propr. Robt. Findlay M'f'g. Co., 349
Adams St., Brooklyn, N. Y.
Shearer, E. P.
Public Service Gas Co., 271 N.
Broad St., Elizabeth, N. J.
TRANSACTIONS I. E. S. — PART II
Smith, A. A.
Public Service Electric Co., Newark,
N.J.
Smith, G. E.
Public Service Electric Co., Newark,
N.J.
Stieren, Edward
Ophthalmologist, WestinghouseBldg.,
Pittsburgh, Pa.
Taxzer, E. Dean
Assistant Professor Electrical En-
gineering, Lafayette College, Eas-
ton, Pa.
Thompson, R. B.
Sales Dept. (Lighting) Central
Hudson Gas & Electric Co., 129
Broadway, Newburgh, N. Y.
Tingley, Louisa Paine
Physician (Ophthalmologist), 9
Massachusetts Ave., Boston, Mass.
Van Gieson, C. J.
Public Service Electric Co., Newark,
N.J.
Walker, J. H.
Assistant Engineer, C. L. Reeder,
921 Equitable Bldg., Baltimore, Md.
Xylander, P.
Public Service Gas Co., 118 Main
St., Hackensack, N. J.
Young, R. R.
Public Service Electric Co., 759
Broad St., Newark, N. J.
The following twenty applicants were
elected members of the society at a
Council meeting held April 8 :
Allen, Chile C.
Superintendent, Geo. S. Johnston
Co., 5 S. Wabash Ave., Chicago, 111.
Ambler, Thomas M.
Manager, Commercial Department,
Brooklyn Union Gas Co., 176 Rem-
sen St., Brooklyn, N. Y.
Brauns, H. E.
District Sales Agent, Milwaukee
Electric Railway & Light Co., 429
Mitchell St., Milwaukee, Wis.
Palmer, Briggs S.
Optometrist, John W. Sanborn Co.,
149 Tremont St., Boston, Mass.
Bryant, Alice G. (M. D.)
502 Beacon St., Boston, Mass.
Callender, D. E.
General Manager, Wisconsin Gas &
Electric Co., 305 6th St., Racine,
Wis.
English, Frank F., 2nd.
Ilhiminating Engineer, 51 E. 42nd
Si., New York, N. Y.
Flynn, M. F.
District Sales Agent, Milwaukee
Electric Railway & Light Co., Public
Service Bldg., Milwaukee, Wis.
Foote, Frank H.
Manager, Specialty Department,
Pettingell-Andrews Co., 511 Atlantic
Ave., Boston, Mass.
Grant, Albert Weston, Jr.
Photometrical Dept., United Gas
Improvement Co., Philadelphia, Pa.
Harris, Arthur C.
District Sales Agent, Milwaukee
Electric Railway & Light Co.,
Racine, Wis.
Jamison, Chas. M.
Manager, Merchandise Sales Dept.,
Milwaukee Electric Railway & Light
Co., Public Service Bldg., Milwau-
kee, Wis.
Johnson, N. E.
Vice-President, The Linden Co.,
1216 Michigan Ave., Chicago, 111.
Kruse, O. J.
District Sales Agent, Milwaukee
Electric Railway & Light Co., Public
Service Bldg., Milwaukee, Wis.
Monger, H. G.
Chief Clerk. Sales Dept., Milwaukee
Electric Railway & Light Co., Public
Service Bldg., Milwaukee, Wis.
TRANSACTIONS I. E. S. — PART II
Montgomery, T. M.
Manager, Lamp Dept., Elliott-Lewis
Electrical Co., Inc., 138-40 N. 10th
St., Philadelphia, Pa.
Pevear, Munroe Rhodes
Architect and Colored Light Special-
ist, Pevear Color Specialty Co. and
Foss & Pevear, Architects, 71
Brimmer St., Boston, Mass.
PvEUTELER, A. C.
Manager, Watertown Gas & Electric
Co., 205 Main St., Watertown, Wis.
Van Derzee, G. W.
Assistant to Vice-President, Mil-
waukee Electric Railway & Light
Co., Public Service Bldg., Milwau-
kee, Wis.
Wall, William L.
Secretary and Treasurer, Wall &
Ocles, Inc., 1716 Chestnut St., Phila-
delphia, Pa.
Sustaining Membership.
The American Gas & Electric Co. of
New York, the Brooklyn Union Gas Co.
and the Edison Illuminating Co. of
Detroit were elected sustaining members
of the society at a Council meeting held
April 8.
The following companies were elected
sustaining members of the society
March 1 1 :
Edison Lamp Works of General Elec-
tric Company, Harrison, N. J.
Schenectady Illuminating Company,
Schenectady, N. Y.
New Books.
Modern Illumixants and Illumi-
nating Engineering — by Leon Gaster
and J. S. Dow ; 458 pp., price $5.00, the
Macmillan Co., New York. Chapters
on : history and development of meth-
ods of illumination; gas lighting; elec-
tric lighting; oil, petrol-air gas and
acetylene lighting; illumination and the
eye; color and the eye; measurement
df light and illumination; globes, shades
and reflectors, and calculations of illumi-
nation ; problems in interior illumina-
tion; outdoor lighting. Bibliography
appended.
Personals.
Mr. Harvey B. Wheeler, formerly
with the National X-Ray Reflector Co.,
Chicago, 111., is now chief engineer of
the Pettingell-Andrews Co., Boston,
Mass.
Prof. Alexander Silverman, director
of the department of chemistry of
University of Pittsburgh has recently
given before several chemical societies
a lecture constituting a survey of the
chemistry and technology of glass mak-
ing. Numerous specimens of glass were
exhibited at each lecture.
Obituary.
George Cutter, vice-president of the
George Cutter Co., South Bend, Ind.,
died of heart failure on April 6, 1915,
in Los Angeles, Cal. He was born near
Boston in 1853. In 1889 he started in
business for himself in Chicago in the
manufacture of electrical appliances. In
1898 he organized the George Cutter Co.,
manufacturers of specialties for outdoor
electric lighting.
TRANSACTIONS
OF THE
Illuminating
Engineering Society
NO. 4, 1915
PART II
Miscellaneous Notes
TRANSACTIONS I. E. S. — PART II
Council Notes.
A meeting of the Council was held
May 13 in the general offices of the
society, 29 West 39th Street, New York,
N. Y. Those present were : A. S.
McAllister, president; C. O. Bond, H.
Calvert, George A. Hoadley, C. A.
Littlefield, general secretary; L. B.
Marks, treasurer; Alten S. Miller,
Preston S. Millar, W. Cullen Morris,
J. Arnold Norcross, and Geo. H. Stick-
ney; upon invitation, George S. Bar-
rows, C. E. Clewell, A. Hertz, and
F. K. Richtmyer.
Reports on section activities were re-
ceived from the following vice-presi-
dents : George A. Hoadley, Philadel-
phia ; Ward Harrison, Pittsburgh ; G. H.
Stickney, New York ; and F. A. Vaughn,
Chicago.
Upon recommendation of the Finance
Committee, vouchers No. 2088 to No.
2095 and No. 2097 to No. 2129 inclusive,
aggregating $921.81, were authorized
paid.
After the reading of a written report
by the chairman of the Committee on
Factory Lighting, it was resolved that
it is the sense of the Council that (1)
the Committee on Popular Lectures
should with due speed complete its lec-
tures in order to have them ready for
service; (2) that when they are com-
pleted, they shall be presented for
action by the necessary committees, and
for approval by the Council; (3) that
immediately upon approval of the Coun-
cil they shall be deemed ready for ser-
vice upon demand ; and that (4) they
shall be printed in the Transactions
after approval by the Council and the
usual committees.
Mr. J. Arnold Norcross, representa-
tive of the I. E. S. on the International
Gas Congress, asked that the society
cooperate in advertising the congress,
which is to be held in San Francisco
next September. It was voted that a
notice concerning the congress be
published in the next issue of the
Transactions.
Mr. C. O. Bond recommended the
appointment of Messrs. G. S. Barrows
and G. E. Hulse to present at the San
Francisco convention of the American
Gas Institute two papers which shall be
credited to the I. E. S.
An oral report was made by Prof.
F. K. Richtmyer, chairman of the Com-
mittee on Education. One member of
the committee is to present a paper
before the coming convention of the
Society for the Promotion of Engineer-
ing Education.
A written report was received from
Mr. Wra. Hand Browne, Jr., delegate
of the I. E. S. to the presidential inau-
gural ceremonies of the University of
North Carolina. It was voted that the
report be acknowledged and a vote of
thanks of the Council be extended to
Mr. Browne.
Informal reports were made by Mr.
G. H. Stickney, chairman of the Com-
mittee on Papers, and Mr. Preston S.
Millar, chairman of the Committee on
Sustaining Membership.
Communications were received from
Messrs. M. M. Marks, president of the
Borough of Manhattan ; S. G. Hibben,
secretary of the Pittsburgh Section, and
C. L. Law.
The following committee appoint-
ments were confirmed :
Committee on Factory Lighting: D.
M. Petty.
Committee of Election Tellers : L. J.
Lewinson, chairman ; H. V. Allen, Edgar
H. Bostock, W. A. D. Evans, and A. L.
Powell.
TRANSACTIONS I. E. S. — PART II
Section Activities.
Chicago Section
Meetings
April 22, 1915. Auditorium, Western
Society of Engineers, Monadnock Build-
ing. Paper : "Knowns and Unknowns
in the Lighting of Small Interiors," by
Mr. James R. Cravath. The paper
appears elsewhere in this issue of the
Transactions. Attendance 51.
May 21, 1915. Auditorium, Western
Society of Engineers, Monadnock Build-
ing. Paper : "Principles of Scientific
Street Lighting," by Mr. A. J. Sweet.
The tentative program of papers for
the June meeting of the Chicago Sec-
tion is as follows :
June — "Lighting of Open Air Spaces :
Streets, Building Exteriors, Signs."
New York Section
Meetings
May 13, 1915. Engineering Societies
Building. Papers: (1) "Illuminating
Engineering as a Branch of Technical
Instruction," by C. E. Clewell; (2)
"Sheet Glass — Its Manufacture and Use
for Illuminating Purposes," by E. H.
Bostock. Attendance 85.
June — To be announced later.
Philadelphia Section
Meetings
April 24, 1915. Joint meeting with
the American Electro-chemical Society
at the University of Pennsylvania.
May 21, 1915. Baltimore. Papers :
(1) "Store Lighting," by Mr. W. R.
Moulton; (2) "A Proposal Relative to
Definitions, Standards and Photometric
Methods," by Dr. H. E. Ives.
Pittsburgh Section
Meetings
May 7, 1915. The Hofbrau, Cleve-
land, Ohio. Papers: (1) "Gas Street
Lighting Development," by Mr. F. R.
Hutchinson; (2) "Street Lighting with
the Modern Arc Lamp," by Mr. W. P.
Hurley; (3) "Recent Developments in
Incandescent Street Lighting," by Mr.
Ward Harrison. Attendance 55.
New Members.
The following three applicants were
elected members of the society at a
meeting of the Council held May 13,
1915 :
Hudson, Ralph Gorton
Instructor of Electrical Engineering,
Massachusetts Institute of Technol-
ogy, Boston, Mass.
Jelliefe, C. N.
Vice-president and Treasurer, Amer-
ican Light & Traction Co., 40 Wall
St., New York, N. Y.
Turner, Hunter Heiner
Ophthalmologist, 517 Jenkins Arcade
Bldg., Pittsburgh, Pa.
Personals.
Mr. J. C. Schmidtbauer has been
elected president of the Milwaukee Elec-
trical League.
Mr. C. W. Bender has been appointed
general manager of the Nela Specialties
Division, recently organized to handle
specialties manufactured by the National
Lamp Works of the General Electric
Company. He will also continue his
present work as manager of the com-
mercial department.
Obituary.
Mr. George Maurice, manager of the
heating and light department of the
General Electric Company, Ltd., of
London, England, and one of the direc-
TRANSACTIONS I. E. S. — PART II
tors of that company, was one of the
passengers reported lost in the sinking
of the steamship Lusitania on May 7,
1915. Mr. Maurice had been in this
country for several weeks on one of
his numerous business trips. He was
widely known in the electrical industry,
both in this country and abroad.
Joint Session A. I. E. E. and I. E. S.
The American Institute of Electrical
Engineers and the I. E. S. will hold a
joint session on Wednesday evening,
June 30, 1915, at Deer Park, Md., in
conjunction with the 32nd annual con-
vention of the institute. Two papers
are scheduled for this session : "Sys-
tems of Street Illumination," by Dr.
C. P. Steinmetz, and "The Effective
Illumination of Streets," by Mr. Preston
S. Millar. Copies of the latter paper
may be had free about June 15 upon
application to the general office of the
I. E. S., 29 West 39th Street, New
York, N. Y.
Results of 1915 I.E. S. Election.
The Committee of Tellers met May
27, 1915, in the general office of the
society, and counted the votes of the
1915 annual election. The results
reported by the committee showed that
the following officers of the society and
its several sections were elected for
various terms beginning October 1, 1915 :
President, Dr. C. P. Steinmetz ; gen-
eral secretary, Alten S. Miller ; treas-
urer, L. B. Marks ; vice-presidents,
Clarence L. Law and J. L. Minick ;
directors, W. A. Durgin, M. Luckiesh,
and J. Arnold Norcross.
Chicago Section — Chairman, E. W.
Lloyd ; secretary, O. L. Johnson ; man-
agers, A. O. Dicker, H. M. Frantz, C. A.
Luther, A. H. Meyer, and F. A. Rogers.
New England Section — Chairman,
Louis Bell; secretary, S. C. Rogers;
managers, J. W. Cowles, W. B. Lancas-
ter, George P. Smith, Jr., H. F. Wallace,
and R. C. Ware.
New York Section — Chairman, D.
McFarlan Moore; secretary, Norman D.
Macdonald; managers, Thomas M.
Ambler, L. H. Graves, W. F. Little,
E. R. Treverton, and Herbert S.
Whiting.
Philadelphia Section — Chairman, G. S.
Crampton ; secretary, L. B. Eichengreen ;
managers, George S. Barrows, Douglass
Burnett, C. E. Clewell, R. B. Ely, and
C. E. Ferree.
Pittsburgh Section — Chairman, Lewis
J. Kiefer; secretary, R. H. Skinner;
managers, Henry Harris, H. S. Hower,
Harold Kirschberg, H. H. Magdsick,
and G. W. Roosa.
The proposals to amend the constitu-
tion of the society were also adopted by
a vote of more than five to one. The
principal amendments include provisions
which create a grade of membership to
be known as members. The require-
ments for admission to this grade, as at
present set forth, are somewhat higher
than those of the other grade of indi-
vidual members known as associate
members. The annual dues of members
will be $10.00 and of associate members
$5.00.
DR. CHARLES P. STEINMETZ
Dr. Charles P. Steinmetz, president-
elect, was born April 9, 1865, at Breslau,
Germany. He was educated at the
gymnasium (high school) and then at
the University of Breslau, where he
studied mathematics and astronomy,
then physics and chemistry, and finally
for a short time medicine and national
economy. Involved in the social demo-
TRANSACTIONS I. E. S. — PART II
cratic agitation against the government,
he escaped to Switzerland in 1888, and
there studied mechanical engineering at
the Polytechnische Zurich.
In 1889 he immigrated to America,
and found a position with the Oster-
held & Eichemeyer Manufacturing Com-
pany, first as draftsman, then as elec-
trical engineer and designer, and finally
on research work in charge of the Eiche-
meyer laboratory.
With the absorption of the Eiche-
meyer interests by the General Electric
Company, Dr. Steinmetz joined the
latter, and was attached to Mr. H. F.
Parshall's calculating department in
Lynn, Mass. With the transfer of the
company's headquarters to Schenectady
in the spring of 1894, Dr. Steinmetz
organized and took charge of the calcu-
lation and design of the company's
apparatus, and of the research and
development work.
For a number of years Dr. Steinmetz
was professor of electrical engineering
at Union University, and at the present
time is professor of electro-physics at
that university, at the same time retain-
ing his connection with the General
Electric Company as chief consulting
engineer. About the year 1910 he
entered into closer relation with this
company by organizing a consulting
engineering department under his
charge.
Among the more important publica-
tions and articles of which he is the
author are a series of papers on each
of the following subjects: polydimen-
tional involutory correspondence ; mag-
netic circuit and the law of hysteresis ;
dielectric and electrostatic phenomena ;
"Design and Performance of Electrical
Apparatus," as transformers, induction
machines, synchronous machines, com-
mutating machines, etc. ; "High Fre-
quency Oscillations and Surges in Elec-
tric Circuits"; "Radiation, Light and
Illumination" ; "Mechanical Thermo-
dynamics and Steam Turbines." Most
of his papers on electrical subjects are
published in the Transactions of the
American Institute of Electrical Engi-
neers.
The following books have been pub-
lished by Dr. Steinmetz : A popular
work on "Astronomy and Meteorology,"
in the German language, 1st edition
1889; "Theory and Calculation of Alter-
nating Current Phenomena," 1st edition
1897, 4th edition 1908; "Theoretical Ele-
ments of Electrical Engineering," 1st
edition 1001, 3rd edition 1909; "General
Lectures on Electrical Engineering," 1st
edition 1908, 4th edition 1910; "Theory
and Calculation of Transient Electric
Phenomena and Oscillations," 1909;
"Radiation, Light and Illumination,"
1909; "Electrical Engineering Mathe-
matics," 1st edition 1910, 2nd edition
1914; "Electric Discharges, Waves and
Impulses," 191 1.
In 1902 Dr. Steinmetz received the
honorary A. M. degree from Harvard
University, and in 1903 the honorary
Ph. D. degree from Union University.
Dr. Steinmetz is president of the
National Association of Corporation
Schools ; vice-president of International
Association of Municipal Electricians ;
honorary president of International
Electrical Congress ; past president of
the American Institute of Electrical En-
gineers; honorary member of the
National Electric Light Association;
fellow of the American Association for
the Advancement of Science ; member
of the (British) Institution of Electrical
Engineers; members of the American
Mathematical Society, the Quaternion
Society, the Society of Mechanical Engi-
neers, Electrochemical Society, Illumi-
TRANSACTIONS I. E. S.— PART II
nating Engineering Society, Physical
Society, and a number of other organi-
zations.
ALTEN S. MILLER
Mr. Alten S. Miller, general secretary-
elect, was born in Richmond, Va., in
1868 and graduated from Stevens Insti-
tute of Technology in 1888 with the
degree of mechanical engineer.
After leaving college he went with
the United Gas Improvement Company
of Philadelphia, and the same year was
sent by that company to Omaha to take
charge of its gas works in that city. In
1892 he was sent to Chicago as western
sales agent of the United Gas Improve-
ment Company and spent two years in
that position.
In 1894 Mr. Miller went to New York,
as engineer of the East River Gas Com-
pany of Long Island City. This com-
pany was then running a tunnel under
the East River and building a plant to
make gas in Long Island City, which
was to be sold in New York. This
company was later consolidated with
one of the New York companies, form-
ing the New Amsterdam Gas Company,
and Mr. Miller was made the engineer
of the latter. While holding that posi-
tion he was made constructing engineer
of the Consolidated Gas Company of
New York in 1900.
In 1902 he became manager of the
Consolidated Gas Company of Balti-
more, Md., and in 1905 was made vice-
president and general manager of the
Consolidated Gas, Electric Light and
Power Company of that city, which fur-
nished all the gas and substantially all
the electricity to the city and vicinity.
While in Baltimore he built a new elec-
tric generating plant to replace the non-
condensing generating plants, and also
a new gas plant to replace three other
manufacturing stations that had become
obsolete.
In 1909 he went to St. Louis as presi-
dent of the Union Electric Light and
Power Company of that city. Here
much was accomplished in reducing
operating expenses and in gaining for
the company the confidence and good
will of the public. Much time was also
spent in valuing the property and in the
other details of a rate case before the
Public Service Commission.
In 191 1 he joined Dr. Alexander
C. Humphreys in the company of
Humphreys & Miller, Inc., of New
York, N. Y. Since then he has confined
his work to consulting engineering. He
has made a special study of valuations
and rate cases in connection with public
service properties.
Besides being a member of the Illumi-
nating Engineering Society, Mr. Miller
is a fellow of the American Institute of
Electrical Engineers and a member of
the National Electric Light Association,
American Gas Institute, American
Society of Mechanical Engineers, Natu-
ral Gas Association, and the Society of
Gas Lighting.
Special Transfer to Grade of Member.
The Council at its meeting held June
10, 1915, approved a special form of
application to be used by Associate
Members in applying for transfer to the
grade of Member. A copy of the form
appears on a following page. Associate
members desiring to apply for transfer
may fill in this form and send it to the
general offices of the Society, 29 West
39th Street, New York, N. Y
Under the amendments to the Con-
stitution which were adopted at the
recent annual election, all members of
the Society passed automatically into a
TRANSACTIONS I. E. S. — PART II
new grade of associate member, except
all general officers of the Society and
members of the general Board of Ex-
aminers.
The dues of members shall be $10.00,
and the dues of associate members
$5.00. All associate members trans-
ferred to the grade of member between
June 10 and October 1, 1915 shall not be
required to pay any additional dues or
fees for the fiscal year ending Septem-
ber 30, 1915.
TRANSACTIONS
OF THE
Illuminating
Engineering Society
NO. 5, 1915
PART II
Miscellaneous Notes
TRANSACTIONS I. E. S. — PART II
Council Notes.
A meeting of the Council was held
June 10, 1915, in the general offices of
the society, 29 West 39th Street, New
York, N. Y. Those present were : A. S.
McAllister, president; E. M. Alger,
C. O. Bond, H. Calvert, L. B. Marks,
treasurer; Alten S. Miller, and G. H.
Stickney.
It was resolved that the names of all
those members owing dues for periods
prior to October 1, 1914, be dropped
from the roll forthwith.
It was resolved that all members
(foreign members excepted as noted
below) owing for current dues be noti-
fied that their names will be dropped
from our roll, in accordance with the
provisions of the Constitution and By-
laws, July 1 if their dues are not paid
in the meantime.
It was further resolved that the names
of delinquent members whose current
dues are unpaid on July 1 be dropped
as of that date. Foreign members shall
be allowed an additional 60 days' time ;
their names to be dropped September 1
unless their dues are received by that
date.
A report on New York Section activi-
ties was received from Mr. G. H.
Stickney.
A report was received from the Com-
mittee of Tellers giving the results of
the annual election which was held in
May. (The results were published,
in accordance with a Co'uncil order, in
the No. 4 issue of the Transactions.)
The Committee on Constitutional Re-
vision submitted (1) a temporary trans-
fer application blank to be used by
associate members in applying for trans-
fer to the grade of member up to Jan-
uary 1, 1916; (2) a new application form
to be used by all applicants in applying
for either the grade of associate member
or member.
The Council directed that the former
application be published in the No. 4
issue of the Transactions and that a
separate blank be sent to each member
of the society at the time of sending one
of the several 1915 convention announce-
ments.
After making a few changes in the
wording of the membership application
form submitted by the committee, it
was ordered that this form be printed
as the one prescribed by the Council,
in accordance with the constitutional
requirements.
It was resolved that all associate
members transferred to the grade of
member before October 1, 1915, shall
not be required to pay any additional
dues for the fiscal year ending Septem-
ber 30, 1915.
A progress report was received from
the Membership Committee.
In accordance with a recommenda-
tion of the committee, the Council
authorized, subject to the approval of
the Finance Committee, an appropriation
of $50.00 for another edition of the
pamphlet on the work and objects of
the society.
In accordance with a recommenda-
tion of the Finance Committee payment
of vouchers No. 2096, and No. 2130 to
No. 2166 aggregating $1,109.58 was
authorized. The Finance Committee
submitted a report showing that the
total receipts from all sources during
the first eight months amounted to
$10,367.28, while the total cash disburse-
ments amounted to $9,620.97.
In a report on the program of papers
for the forthcoming convention of the
society in Washington, the Committee
on Papers stated that it had an unusually
large number of excellent papers under
TRANSACTIONS I. E. S. — PART II
consideration. The number of papers
of a commercial character scheduled for
this year's program will in all probability
necessitate separate sessions for them
on two of the four days of the con-
vention.
The Committee on Lighting Legisla-
tion reported that it expected to submit
during the summer a final proof of a
code on factory lighting. Copies of the
code are to be available for distribution
at the convention.
A progress report was received from
the Committee on Popular Lectures and
accepted with thanks.
Section Activities.
Chicago Section
June 22, 19 15. Auditorium, Western
Society of Engineers, Monadnock Build-
ing. Prof. Edw. L. Nichols of Cornell
University gave a most interesting his-
torical talk on the subject of "Artificial
Lighting in 1900 and 1915," which was
a resume of the progress made in
illumination up to 1915. An interesting
and lively discussion followed the pres-
entation of the paper. Mr. W. A.
Durgin then announced the incoming
officers for the next year and adjourned
the meeting. An enjoyable dinner was
held previous to the meeting at the
Grand Pacific Hotel.
New York Section
June 14, 1915. Brevoort Hotel, 5th
Avenue and 8th Street, New York City.
Short talks on "What the Other Fellow
Knows about Lighting Requirements"
were given by Messrs. Charles W.
Leavitt, landscape architect ; Robert I.
Aitken, sculptor ; Harry Rowe Shelly,
musician ; E. J. Simmons, mural painter,
and Horace Moran, architect. Forty-
eight members and guests were present.
Pittsburgh Section
The final meeting of the year, held
June 11, 1915, included an inspection
trip to several factories of the United
States Glass Company and a dinner.
The members and guests met at the
offices of the glass company at 8.00 p. m.
and an exceptionally interesting trip was
made through departments where the
pressing and blowing of glass was being
carried on. At 10 o'clock a special car
transferred the party to the Fort Pitt
Hotel, Dutch room, and there followed
a dinner with several unique features.
Souvenir drinking tumblers, etched with
the society monogram and an appro-
priate legend, were given to those pres-
ent. Addresses were made by members
of the retiring and incoming boards of
managers.
Personals.
Mr. L. B. Eichengreen has resigned
as secretary of the Philadelphia Section.
Mr. R. B. Ely has been appointed to
succeed Mr. Eichengreen.
Mr. E. W. Lloyd of the Chicago Edi-
son Company has been elected president
of the National Electric Light Associa-
tion for the coming year.
Mr. Frederick Schwartz, for the past
sixteen years with Shapiro & Aronson,
and until recently their store manager,
has resigned to become treasurer and
member of the recently incorporated
concern of Robert Findlay Manufac-
turing Co., designers and manufacturers
of lighting fixtures. Mr. Schwartz will
be in immediate charge of the New
York City salesrooms.
Prof. D. W. Blakeslee has resigned
his position as assistant professor of
electrical engineering in the University
of Arkansas and is now in the engineer-
TRANSACTIONS I. E. S. — PART II
ing department of the Carnegie Steel
Company, Farrell, Pa.
Mr. S. E. Shaff, formerly connected
with the University at Iowa City, is now
with the Electric Machinery Company,
Minneapolis, Minn.
Obituary.
Mr. James P. Maila, chief electrician
for Armour & Company. Chicago, died
on May 29, as the result of an operation
for appendicitis. He had been with
Armour & Company for 29 years and
since 1894 had been chief electrician.
He had charge of the electrical work
in all of the company's plants. He was
a member of the Jovian Order, of the
Illuminating Engineering Society, and
of the Electric Club of Chicago.
New Members.
The following seven applicants were
elected members of the society at a
meeting of the Council held June 10,
1915:
Houghton, C. P.
Second Vice-president, Los Angeles
Gas & Electric Corporation, 645 S.
Hill. St., Los Angeles, Cal.
Humphry, George William
Illuminating Engineer, Armstrong,
Whitworth, Ltd., 4 Cottenham St.,
Newcastle-on-Tyne, England.
Jellett, Stewart A.
Consulting Engineer, 1718 Real Es-
tate Trust Bldg., Philadelphia, Pa.
Kirk, James J.
Illuminating Engineer, Common-
wealth Edison Co., 72 W. Adams
St., Chicago, 111.
Swayne, H. B.
General Contract Agent, Penn Cen-
tral Light & Power Co., 1414 Elev-
enth Ave., Altoona, Pa.
Van Winkle, Frank D.
Treasurer, The Post Glover Elec-
tric Co., 314 W. Fourth St., Cincin-
nati, Ohio.
Wilson, Frank S.
Electrical Engineer, 8 Irvington St.,
Boston, Mass.
Sustaining Members.
The Portland (Me.) Gas Light Com-
pany and the Providence (R. I.) Gas
Company were elected sustaining mem-
bers at a meeting of the Council held
June 10, 1915.
Program of 1915 Convention.
Following is a draft of the prelimi-
nary program of the ninth annual con-
vention of the Illuminating Engineering
Society which is to be held at the New
Willard Hotel, Washington, D. C, Sep-
tember 20-23 inclusive. The papers,
which promise to be of an unusually
high standard, are to be distributed over
ten sessions. One of the sessions will
be devoted especially to the subject of
street lighting ; commercial, general, and
laboratory papers will each be given
three sessions. Inspection trips, a recep-
tion, and a banquet are among the enter-
tainment features.
PROGRAM.
Sept. 20 — (Morning).
Formal opening of convention.
Address of Welcome; President's ad-
dress, etc.
Reports of Committees on Lighting Leg-
islation, Nomenclature and Stand-
ards, and Progress.
Sept. 20 — (Afternoon).
General Session.
Tests and Experiments in Connection
with the New Commonwealth Edi-
TRANSACTIONS I. E. S. — PART II
son Company Building, by Messrs.
W. A. Durgin and J. B. Jackson.
Ship Lighting, by H. A. Hornor.
Illumination Efficiency as Obtained in
an Experimental Room, by Ward
Harrison.
Sept. 20 — (Evening).
Reception.
Sept. 21 — (Morning).
General Session.
Photometry with Portable Instruments,
by W. F. Little.
New Test Plate for Illumination Pho-
tometers, by C. H. Sharp.
Incandescent Lamp Testing and Pho-
tometry, by G. W. Middlekauff.
Street Lighting, by F. A. Vaughn.
Sept. 21 — (Afternoon).
Entertainment, trips.
Sept. 21 — (Evening).
Street Lighting Session.
Gas Street Lighting. (Author not yet
announced.)
Arc Lamps for Street Illumination, by
H. E. Clifford.
New Types of Incandescent Lamps and
Their Relation to the Street Light-
ing Problems, by W. H. Rolinson.
Ornamental Street Lighting, by T. I.
Jones.
Sept. 22 — (Morning).
Commercial Session.
How to Attack a Lighting Problem, by
W. R. Moulton.
How can a Combination Gas and Elec-
tric Company Render the Best Ser-
vices to Customers ? by Messrs. S. B.
Burrows and N. H. Potter.
Small Incandescent Lamps and Special
Illumination Problems, by R. P.
Burrows.
Lighting of Office Buildings, by A. O.
Dicker.
Laboratory Session.
Crova's Method of Colored Light Pho-
tometry Applied to Modern Incan-
descent Illuminants, by Messrs. H.
E. Ives and E. F. Kingsbury.
Differences in Threshold and Acuity
Variations, by P. W. Cobb.
Visual Efficiency, by Messrs. Richtmyer
and Howes.
Yellow Screens, by M. Luckiesh.
Sept. 22 — (Afternoon).
Commercial Session.
The Flame Pilot Ignition of Incandes-
cent Gas Lamps, by C. W. Jordan.
Practical Illumination as Exemplified by
Some Recent Installations of Incan-
descent Gas Lamps, by R. F. Pierce.
Mercury Arc Lamps for Industrial
Lighting, by W. A D. Evans.
Relation between Proper Illumination
and Accident Prevention, by R. E.
Simpson.
Laboratory Session.
Retinal Sensibilities in Relation to Illu-
minating Engineering, by P. G.
Xutting.
The Effect of Distribution of Light on
Muscular Control, by H. M. John-
son.
Effect of Various Wave-lengths of
Radiation on Eye Cataract, by W. E.
Berge.
Sept. 23 — (Morning).
Commercial Session.
Artificial Illumination of Interiors, by
David Crownfield.
Lighting of State, War and Navy Build-
ings, by W. E. Chapman.
Lighting of Gymnasiums and Armories
with Incandescent Lamps, by Messrs.
A. L. Powell and A. B. Oday.
TRANSACTIONS I. E. S.— PART II
Laboratory Session.
The Effect of Surrounding Gas on an
Incandescent Filament, by C. F.
Lorenz.
The Parabolic Mirror, by F. A. Ben-
ford, Jr.
A paper (subject to be announced later)
by C. E. Ferree.
Sept. 23 — (Afternoon).
General Session.
Artificial Illumination in Practical Pho-
tography, by C. E. K. Mees.
Photographic and Visual Illumination
Efficiencies, by L. A. Jones.
Production and Application of Ultra-
Violet Light, by M. Von Reckling-
hausen.
A Flux Method of Obtaining Average
Illumination, by Messrs. T. A. Ben-
ford and H. E. Mahan.
Information regarding the convention
may be had upon application to the gen-
eral office of the society, 29 West 39th
Street, New York.
International Gas Congress.
The International Gas Congress will
be held in San Francisco during the
week of September 27 to October 3.
Details regarding special trains for dele-
gates, hotel accommodations, papers,
etc., may be had upon application to
Mr. George G. Ramsdell, 29 West 39th
Street, New York, N. Y. The fee of
the congress is $5.00, which entitles the
member to a copy of the published
proceedings.
Among the features of particular
interest to gas men at the Panama-
Pacific Exposition are the special instal-
lations of gas lighting, and the gas
exhibit. There are several miles of
high pressure gas lighting. The "Joy
Zone" of the exposition is illuminated
by gas lamps concealed in ornamental
lanterns. In the Court of Abundance
there are gas fountains with serpents
hissing streams of lighted gas. The
effect is both unique and charming.
The gas exhibit in the Palace of Manu-
factures covers a floor space of 10,000
square feet and includes a variety of
interesting displays having to do with
the manufacture, distribution and use
of gas.
TRANSACTIONS
OF THE
Illuminating
Engineering Society
NO. 6, 1915
PART II
Miscellaneous Notes
TRANSACTIONS I. E. S. — PART II
Washingto* C«
itioa Papers.
Below is a condensed outline of the
papers and reports to be presented at
the ninth annual convention of the
Illuminating Engineering Society, to be
held at the New Willard Hotel, Wash-
ington, D. C, September 20-23, 1915.
The summarized statements indicate that
the papers are replete with new and
valuable information on practically every
phase of lighting. Many of the papers
cover extensive special investigations
conducted by authorities of high stand-
ing. For the commercial man or the
solicitor who is interested chiefly in sell-
ing more and better lighting service
there are a number of especially inter-
esting contributions. Advance copies of
practically all the papers and reports
will be available for distribution by
September 18 at the general office of
the society, 29 West 39th Street, New
York, N. Y.
Papers and Reports.
1 — Report of Committee on Nomencla-
ture and Standards.
An annual report containing new
terminology, definitions, symbols,
etc.
2 — Report of the Committee on Light-
ing Legislation.
A comprehensive statement of the
status on lighting legislation; in-
cludes a code on lighting which
was drafted by the committee.
3 — Report of the Committee on Re-
search.
Includes results of an extended
investigation of the various meth-
ods of heterochromatic photom-
etry.
4 — Report of the Committee on Prog-
ress.
Reviews the features of fighting
progress during the last year. For
the most part the report, which is
rather a long one, is a summary
of published matter ; but it also
contains much valuable informa-
tion not heretofore on general
record.
5 — Lighting of Ships, by H. A. Hornor.
The requirements of ship and
marine lighting are set forth ;
methods of wiring and details of
fixtures are discussed.
6 — Lighting of a Passenger Steamer,
by H. F. Spaulding.
Sketches past and present prac-
tise in marine lighting. Lighting
requirements of a passenger boat
are discussed and compared with
similar installations ashore. De-
scribes the lighting system on the
S. S. Noronic, a lake passenger
boat, and includes illumination
test data.
7 — Life Testing of Incandescent Lamps
at the Bureau of Standards,
by G. W. Middlekauff, J. F.
Skogland, and B. Mulligan.
Outlines the methods of tests
and inspections followed by the
United States Bureau of Stand-
ards, and includes a description of
laboratory equipment.
8 — Use of Portable Photometers, by
W. F. Little.
Outlines desirable procedure in
the conduct of photometric tests
with portable apparatus. Dis-
cusses the planning of a survey,
and precautions which should be
taken; a method of testing can-
dlepower, illumination intensity
and brightness ; maintenance of
photometric apparatus ; photo-
metric errors and means of avoid-
ing them.
TRANSACTIONS I. E. S. — PART II
9— Compensating Illuminating Test-
Plates, by C. H. Sharp.
A discussion of the various errors
inherent in illumination test-plates
in use and a description of a new
form of construction which has
been devised to eliminate those
errors.
io— Illumination Efficiencies as Deter-
mined in an Experimental
Room, by Ward Harrison and
Earl A. Anderson.
A report on a series of illumina-
tion tests performed in a portable
room designed for the purpose.
The room dimensions and the
arrangement of the outlets were
varied to approximate the diverse
conditions encountered in prac-
tise. Wall, ceiling and floor com
binations of white, black and inter-
mediate colors were tested with
units of three general types of
light distribution.
ii— Semi-direct Office Lighting of the
Chicago Edison Building, by
W. A. Durgin and J. B.
Jackson.
Gives a description of a typical
office and comparative tests on five
lighting systems, showing the rela-
tive eye fatigue, glare, shadows,
etc. Data are given on the illumi-
nating effectiveness, appearance,
dust factor, etc., for the complete
installation.
12— Street Lighting with Gas Lamps, by
Geo. S. Barrows.
A discussion of modern street
lighting with gas.
13— Arc Lamps for Street Illumination,
by H. E. Clifford.
Outlines recent developments and
characteristics of arc lamps de-
signed for street illumination.
14 — New Types of Incandescent Lamps
and Their Relation to Street
Lighting Problems, by W. H.
Rolinson.
A brief historical review and con-
sideration of the fundamental
requisites of street lighting; vari-
ous systems are classified accord-
ing to unit and location. The
choice of illuminants, means of
regulation and general equipment
are also discussed. Special atten-
tion is given to the recent develop-
ments in electric incandescent
lamps for street lighting.
15 — Application of Principles of Scien-
tific Street Lighting, by F. A.
Vaughn.
A comprehensive statement of the
requirements of street lighting
based upon a special investigation
conducted in Milwaukee, Wis.
16 — How Can a Combination Gas and
Electric Company Render the
Best Service to the Customer?
by A. B. Spaulding and H. N.
Potter.
Deals with the question of proper
service to the customer; the edu-
cation of salesmen and the cus-
tomer; the relation between the
salesman and the customer ; and
the question whether the sale of
gas and electric illumination
should be handled on a competi-
tive basis or by combination men.
17 — The Selection of a Standard Unit
for Lighting, by W. H. Moul-
ton.
Discusses the problem of selecting
a new style of standard fixture
for commercial work. Features
of various lighting units are out-
lined.
TRANSACTIONS I. E. S. PART II
18 — Small Incandescent Lamps and
Special Illumination Problems,
by R. P. Burrows.
Deals with improvements in the
manufacture of small incandes-
cent lamps for novelties and the
industrial and medical fields. A
number of the present applications
of these lamps are mentioned.
19 — Illumination and One Year's Acci-
dents, by R. E. Simpson.
Gives results of a study of one
year's industrial accident records,
the purpose of which was to deter-
mine the effect of the lighting
conditions on the causation of
accidents. Typical accidents are
mentioned to show how lighting
conditions have been responsible
for injuries to workmen.
20 — The Application of Crova's Method
of Colored Light Photometry
to Modern Incandescent Illu-
minants, by H. E. Ives and
R. F. Kingsbury.
Discussion of the advantages and
. requirements of Crova's method
for overcoming color differences
in heterochromatic photometry.
21 — The Relative Photographic and
Visual Efficiencies of Light
Sources, by L. A. Jones, M. B.
Hodgsen and Kenneth Russ.
Sets forth the relation between
the visual and photographic effi-
ciencies of various lighting
sources. Methods for the deter-
mination of these relations are
outlined. A large amount of data
is included to show the relations
between several sources and three
types of photographic plates.
22— A Method for Studying the Behav-
ior of the Eye Under Differ-
ent Conditions of Illumina-
tion, by F. K. Richtmyer and
H. L. Howes.
Describes a method of studying
visual efficiency which gives indi-
cations of being well adapted to
quantitative measurements of the
manner in which different condi-
tions of illumination affect the
working eye. Several curves are
included to show the resemblances
and differences in the rates of
reading various matter by several
observers. Other curves show the
effects produced by placing frosted
and unfrosted lamps in the field
of vision.
23 — The Flame Pilot Ignition of Incan-
descent Gas Lamps, by C. W.
Jordan.
Features, advantages, and the
application of various methods and
systems of pilot ignition are dis-
cussed.
24 — Practical Illumination as Exempli-
fied by Some Recent Installa-
tions of Incandescent Gas
Lamps, by R. F. Pierce.
A report on the various recent
installations of gas lamps.
25 — Mercury-vapor Lamps for Indus-
trial Lighting, by W. A. D.
Evans.
Outlines the lighting requirements
of various industries, special ref-
erence being made to the applica-
tion of the mercury-vapor lamp.
26 — The Retinal Sensibilities Related to
Illuminating Engineering, by
P. G. Nutting.
Points out the retinal sensibilities
of importance in illuminating en-
gineering, such as sensibility to
brightness and brightness differ-
ences and to color and color
differences. The inter-relations
of these sensibilities are outlined
and methods given for their quan-
titative determination. The best
data on each sensibility, including
TRANSACTIONS I. E. S. — PART II
much that is new, are summarized
in each case.
27 — Vision and Brightness of Surround-
ings, by P. W. Cobb.
Outlines the results of an investi-
gation of visual acuity and differ-
ence-threshold. Describes new
apparatus and methods used.
28 — A Flux Method of Obtaining Aver-
age Illumination.
Describes a method of obtaining
the average illumination from a
lighting installation on the basis
of the total flux generated by
the light sources. The lower
hemisphere surrounding the light-
ing unit is divided in three 300
zones, and the lighting unit classi-
fied according to the percentage
of flux delivered in these zones.
Having determined the proper
classification for any lighting unit
by means of one or more of the
graphic charts shown, one is
enabled to calculate the flux inci-
dent on the floor area for each
unit and by adding these together
determine the flux over the entire
floor space.
29 — Artificial Illumination of Architec-
tural Interiors, by David
Crownfield.
Deals with the lighting require-
ments of large interiors of differ-
ent architectural styles and classes.
30 — Artificial Lighting of Typical Offices
in the State, War, and Navy
Department Building, by W.
E. Chapman.
Gives a brief description of the
lighting conditions in a typical
office of this building, which was
erected in 1886. The present
lighting requirements, and a de-
scription of the latest remodelled
installation employing tungsten
lamps are given.
31 — Lighting in Downtown Office Build-
ings, by A. O. Dicker and J. J.
Kirk.
Contains a description of typical
downtown office buildings in the
city of Chicago, representative of
periods thirty, twenty, fourteen
and six years ago. The lighting
in these buildings is contrasted
with an installation in a recently
completed building in the same
district.
32 — Present Practise in the Lighting of
Armories and Gymnasiums
with Tungsten Filament
Lamps, by A. L. Powell and
A. B. Oday.
Gives descriptions and tabular
tabular data on the lighting re-
quirements of numerous armories
and gymnasiums.
33 — Ultra-violet Light and the Eye, by
W. R. Burge.
An investigation to determine
which wave-lengths in the ultra-
violet region of the spectrum are
harmful to living tissue, and the
mode of action of these wave-
lengths in producing injury.
34 — Production and Application of
Ultra-violet Rays, by M. von
Recklinghausen.
A brief description of the differ-
ent sources of ultra-violet rays.
Includes a short description of
the salient features of the system
of sterilization of water by ultra-
violet rays, and several pictures
of recent plants.
35 — The Parabolic Mirror, by F. A.
Benford.
Directs attention to the increasing
importance of parabolic reflectors
for the projection of light for
military and naval service, trans-
portation, flood lighting and spec-
tacular illumination. For the most
TRANSACTIONS I. E. S. — PART II
part a mathematical treatment of
the reflector used with point,
spherical and disk sources. Prob-
ably the most complete treatment
of the theory of the reflector that
has thus far been presented.
36 — Some Experiments on the Eye with
Inverted Reflectors of Differ-
ent Densities, by C. E. Ferree
and G. Rand.
The fourth of a series of papers
in which the effect of the various
conditions of lighting on the eye
is investigated. Gradation of sur-
face brightness is made the chief
variable. Semi-direct reflectors
of six degrees of density are
employed and a correlation is
made between the illuminating
effects obtained and the tendency
to cause loss of visual efficiency
and to produce ocular discomfort.
2,7 — The Effect of Variation of Atmos-
pheric Pressure on the Can-
dlepower of Flames, by E. B.
Rosa. E. C. Crittenden and
A. H. Taylor.
A summary of an investigation
conducted at the United States
Bureau of Standards.
38 — Yellow Light, by M. Luckiesh.
Knowns and unknowns and the
various opinions regarding yellow
light are briefly discussed with
respect to visual acuity, glare,
fatigue, penetrating power, and
esthetic value. Outlines the pro-
cedure involved in altering the
light from tungsten lamps to
match a light from the kerosene
flame or the old carbon incan-
descent lamp.
39 — Artificial Illuminants for Use in
Practical Photography, by
C. E. K. Mees.
Illuminants differ in efficiency,
quality, size of source, consistency
and flicker. Tables are given
showing a classification of illumi-
nants according to these charac-
teristics when they are to be used
with each of three classes of sen-
sitive photographic materials :
those sensitized to the whole
spectrum, those with their sensi-
tiveness in the blue violet, and
those sensitive only to the ultra-
violet. Another table shows a
classification of various available
artificial light sources according
to the photographic operations
for which they are suitable.
Personals.
Prof. W. S. Franklin has resigned as
professor of physics at the Lehigh Uni-
versity, Bethlehem, Pa., with which he
had been associated since 1897. He is
now planning an extensive lecture tour
of American universities and engineer-
ing schools.
Alfred O. Dicker, who for the greater
part of the last six years has been con-
nected with the illuminating engineering
division of the contract department of
the Commonwealth Edison Company,
Chicago, has organized with two asso-
ciates the Electrical Sales Engineers,
Inc., with offices at 19 South Fifth Ave-
nue, Chicago.
Robert S. Orr, who is general mana-
ger of the Duquesne Light Company,
Pittsburgh, Pa., was elected fourth vice-
president of the National Electric Light
Association at its convention at San
Francisco in June.
Mr. Walter Neumuller. who for the
past five years has been assistant secre-
tary of the Association of Edison Illu-
minating Companies, has been appointed
special representative of the New York
Edison Company. He is also a director,
TRANSACTIONS I. E. S. — PART II
treasurer and assistant secretary of the
Electrical Show Company, director and
treasurer of the New York Electric
Vehicle Association, and director and
member of the executive committee of
the Electrical Refrigerating Company.
Mr. Joseph D. Israel, district manager
for the Philadelphia Electric Company,
was elected recently to serve as chair-
man of next year's convention of the
sales managers of Edison illuminating
companies.
Dr. A. S. McAllister, president of the
Illuminating Engineering Society, re-
signed the editorship of the Electrical
World, August I, 1915.
New Book*.
Standard Handbook for Electrical
Engineers, compiled by Frank F. Fowle
and a staff of specialists; 1984 pp., $5.00;
McGraw-Hill Book Company, Inc., 239
West 39th Street, New York, N. Y.
Contains chapters on the following top-
ics : illumination ; units, conversion fac-
tors and tables ; electric and magnetic
circuits ; measurements and measuring
apparatus ; properties of materials ;
magnets, induction coils, condensers
and resistors ; transformers and recti-
fiers ; alternating-current generators and
motors ; direct-current generators and
motors ; converters and double-current
generators ; power plants ; power trans-
mission; distribution systems; interior
wiring; industrial motor applications;
electric railways ; electric commercial
vehicles ; electric ship propulsion ; elec-
trochemistry; batteries; telephony, teleg-
raphy and radiotelegraphy ; miscella-
neous applications of electricity; me-
chanical section; standardization rules
of the American Institute of Electrical
Engineers ; general engineering econo-
mics and central station economics.
The chapter on Illumination deals
with production of light, incandescent
lamps, carbon filament, metallized carbon
filament, tantalum, tungsten, gas-filled
type ; arc lamp characteristics, carbon-
electrode, flame arc, metallic electrode,
tube lamps, lighting accessories, reflec-
tors, indirect and semi-indirect lighting;
illumination calculations, flux, candle-
power, intensity, brightness, efficiency ;
applied illumination, fundamentals of
vision, characteristics of illumination,
physiological and psychological effects,
methods, design, costs ; photometry,
fundamentals, standards, apparatus,
spectrophotometers, colorimeters, and
testing.
Section Notes.
The programs of meetings and papers
of the several sections of the society
for the coming season will be announced
in the next issue of the Transactions.
TRANSACTIONS
OF THE
Illuminating
Engineering Society
NO. 7, 1915
PART II
Miscellaneous Notes
TRANSACTIONS I. E. S. — PART II
Section Notes.
New York Section
Meetings
October 14, 1915. Engineering So-
cieties Building. Papers: (1) "Illumi-
nation in the Navy," by Lieut. C. S.
McDowell of the Brooklyn Navy Yard;
(2) "Illumination in the Army," by
Capt. Edward D. Ardery, Corps of Engi-
neers, U. S. Army. Attendance 85.
The following tentative program for
the rest of the year has been announced :
November — A joint meeting with
the American Electro-chemical Society.
Papers on luminous gases by Messrs.
D. McFarlan Moore and Walter V.
Cady.
December — A paper on stage lighting.
January — A paper on lighting trans-
mission and optical instruments by Dr.
F. L. G. Kollmorgen; and a paper on
projector lamps.
February — Joint meeting with the
American Society of Mechanical Engi-
neers. Mr. C. E. Clewell will present a
paper on the factory lighting code of
the Illuminating Engineering Society.
March — A lecture on illuminating
engineering by Dr. Charles P. Steinmetz.
April — Papers on gas subjects.
May — Papers on street lighting.
June — Fine arts meeting.
Philadelphia Section
The following program of the Phila-
delphia Section has been announced :
October 15 — "Opportunities in the
Lighting Field," by Norman Macbeth,
Editor, Lighting Journal.
November 8 — Joint meeting with
Philadelphia Section of American Insti-
tute of Electrical Engineers. "New
Code of Lighting for Factories, Mills
and Other Work Places," by Prof. C. E.
Clewell, Department of Electrical Engi-
neering, University of Pennsylvania.
November 19 — "Coal Mine Illumina-
tion and Its Relation to Accident Pre-
vention and Miners' Nystagmus," by
R. E. Simpson, Engineer, The Travelers'
Insurance Company.
December 17 — Joint meeting with
Engineers' Club. "Illuminating Engi-
neering," by Charles P. Steinmetz, A. M.,
Ph. D., President, Illuminating Engineer-
ing Society; Chief Consulting Engineer,
General Electric Company.
January 21 — "Illumination Problems at
the Panama-Pacific Exposition," by
W. D'A. Ryan, Illuminating Engineer,
General Electric Company.
February 18 — ."Tests of Street Illumi-
nation," by Preston S. Millar, Past-
president, Illuminating Engineering
Society ; General Manager, Electrical
Testing Laboratories.
March 13 — Joint meeting with Phila-
delphia Section, American Institute of
Electrical Engineers. "Engineering
Training as a Business Asset," by
Charles F. Scott, Sc. D.. Past-president,
American Institute of Electrical Engi-
neers ; Professor of Electrical Engineer-
ing, Sheffield Scientific School of Yale
University.
March 17 — "Lighting Legislation," by
L. B. Marks, Past-president, Illuminat-
ing Engineering Society; Consulting
Engineer.
April 21 — "Type C Lamps in Street
Lighting," by T. J. Pace, Commercial
Engineer, Westinghouse Electric &
Manufacturing Company.
May 19 — "Educational Aspects of
Illumination," by Prof. F. K. Richt-
myer, Chairman, Committee on Educa-
tion, Illuminating Engineering Society.
June 16 — "Artificial Lighting for a
Hundred Years," by William J. Serrill,
Engineer of Distribution, United Gas
Improvement Company.
TRANSACTIONS I. E. S. — PART II
Annual Convention.
The ninth annual convention of the
Illuminating Engineering Society was
held at the New Willard Hotel hi Wash-
ington, D. C, September 20-23 inclusive.
There were twelve sessions, three of
which were devoted to technical or labo-
ratory subjects, three to commercial
papers, one to street lighting, and the
remaining four to general topics. All
sessions were well attended and brought
out a large amount of lively discussion.
Among the entertainment features were
a reception by Washington members and
guests at the New Willard Hotel on
Monday evening, September 20 ; a recep-
tion at the White House by President
Woodrow Wilson at noon Tuesday; a
drill by the United States Cavalry at
Fort Myer, Va. ; automobile trips for
the ladies; and the annual banquet. A
"get together" luncheon and discussion
of society affairs was held on Thursday.
The total registration was 350, includ-
ing members and their guests. Without
question the convention was a success
and a fitting climax for the year's activi-
ties of the society.
New Members.
The following five applicants were
elected associate members at a Council
Executive Committee meeting held
August 5 :
Howe, Ralph Sawyer
Illuminating Engineer, Mitchell
Vance Company, 24th Street and
Broadway, New York, N. Y.
KOCHERSPERGER, JEROME
Assistant Sales Engineer and
Draughtsman, Central Electric Com-
pany, 320 South Fifth Avenue,
Chicago, 111.
Myer, Albert
Optometrist, 244 Broadway, Albert
Lea, Minn.
Walker, Edmund Ernest
Sales Engineer, Light and Power
Department, British Columbia Elec-
tric Railway Company, Ltd., Canal
Street, Vancouver, B. C.
Willey, Llewellyn M.
District Manager, Diehly Manufac-
turing Company, 1017 West Jackson
Boulevard, Chicago, 111.
At a meeting of our Council Executive
Committee held August 18, the follow-
ing applicants were elected associate
members :
Bolton, Frank C.
Professor of Electrical Engineering,
Agricultural and Mechanical Col-
lege of Texas, College Station, Tex.
Cressman, Russell B.
Sales Department, Gleason Tiebout
Glass Company, 71 West 23rd Street,
New York, N. Y.
Taylor, A. Hadlay
Assistant Physicist, Bureau of
Standards, Washington, D. C.
The following fifteen applicants were
elected associate members at a meeting
of the Council Executive Committee
held September 23 :
Anderson, Earl A.
National Lamp Works, General
Electric Company, Nela Park, Cleve-
land, Ohio.
Burrows, Robert P.
Electrical Engineer, National Lamp
Works of General Electric Com-
pany, Nela Park, Cleveland, Ohio.
Chapman, F. W.
Director, Technological Department,
Newberry College, Newberry, S. C.
TRANSACTIONS I. E. S. PART II
Coe, Gilbert A.
Lighting Service Department, Phila-
delphia Electric Company, iooo
Chestnut Street, Philadelphia, Pa.
Dorting, E. E.
Lighting Engineer, Interborough
Rapid Transit Company, 600 West
59th Street, New York, N. Y.
Fuller, William J.
Illuminating Expert, Consumers' Gas
Company, 19 Toronto Street,
Toronto, Canada.
Hellmann, C. B.
Salesman, Luminous Unit Company,
2615 Washington Avenue, St. Louis,
Mo.
Howard-Soler, Antonio
L. K. Comstock & Company, 30
Church Street, New York, N. Y.
Little, Arlington P.
Assistant Physicist, Bureau of
Standards, Pierce Mill Road, Wash-
ington, D. C.
Lord, Albert C.
Purchasing Agent, Northern Union
Gas Company, 1815 Webster Ave-
nue, New York, N. Y.
Palmer, H. C.
Engineer, Buffalo Gas Company, 186
Main Street, Buffalo, N. Y.
SCHLADT, G. J.
Laboratory Assistant in Photometry,
Bureau of Standards, Washington,
D. C.
Smith, Esmond M.
Beardslee Chandler & Manufactur-
ing Company, 216 South Jefferson
Street, Chicago, 111.
Sullivan, A. H.
Manager and Electrical Engineer,
Columbia Electric & Engineering
Company, 144 North 14th Street,
Lincoln, Neb.
Wilhoite, L. J.
Contract Agent, Chattanooga Rail-
way & Light Company, 710 Market
Street, Chattanooga, Tenn.
New Sustaining Members.
The following companies were elected
sustaining members at a Council Execu-
tive Committee meeting held August 5,
1915:
Utah Gas & Coke Company
Salt Lake City, Utah.
St. Louis Brass Manufacturing Com-
pany
St. Louis, Mo.
Transfers.
The following applicants have been
transferred from the grade of associate
member to the grade of member :
August 18, 1915.
Abbott, Arthur L.
Manager, Electric Construction
Company, 174 East 6th Street, St.
Paul, Minn.
Auty, K. A.
Chief Illuminating Engineer, British
Columbia Electric Railway Com-
pany, Ltd., 1 193 Bender Street,
West, Vancouver, B. C.
Blakeslee, Dorap Wilmot
Engineering Department, Carnegie
Steel Company, Farrell, Pa.
Bond, Charles O.
Manager, Physical Laboratory,
United Gas Improvement Company,
3101 Passyunk Avenue, Philadelphia,
Pa.
Clewell, C. E.
Assistant Professor of Electrical
Engineering, University of Pennsyl-
vania, Philadelphia, Pa.
Crownpield, David
Chief Designer and Illuminating
Engineer, Pettingell-Andrews Com-
pany, 160 Pearl Street, Boston,
Mass.
TRANSACTIONS I. E. S. — PART II
Dates, Henry B.
Professor of Electrical Engineering.
Case School of Applied Science,
Euclid Avenue, Cleveland, Ohio.
Durgin, Wm. A.
Testing Engineer, Commonwealth
Edison Company, 28 North Market
Street, Chicago, 111.
Evans, William A. D.
Commercial Engineer. Cooper-
Hewitt Electric Co.. 730 Grand
Street, Hoboken. X. J.
Foster, Spottswood C.
Superintendent and Electrical Engi-
neer. Rappahannock Electric Light
& Power Company, Charles and
Amelia Streets, Fredericksburg, Va.
Floy, Henry
Consulting Engineer. 165 Broadway.
New York, N. Y.
Grondahl, Lars O.
Assistant Professor of Physics,
Carnegie Institute of Technology.
Pittsburgh, Pa.
Gradle, Harry S.
Ophthalmologist, 32 North State
Street, Chicago, 111.
Jackson, J. B.
Engineer of Lighting Service, Com-
monwealth Edison Company, 72
West Adams Street, Chicago, 111.
Johnson, Otis L.
Illuminating Engineer, Benjamin
Electric Manufacturing Company,
120 South Sangamon Street, Chi-
cago, 111.
Kirschberg, Harold
Consulting Illuminating Engineer,
650 Century Building, Pittsburgh.
Pa.
Kellogg, Raymond Clinton
Assistant to Superintendent of
Street Department (District No. 2),
Brooklyn Union Gas Company, 176
Remsen Street, Brooklyn, N. Y.
Lacombe, Charles F.
Consulting Engineer, 30 Broad
Street, New York, N. Y.
Lansingh, Van Rensselaer
President, The By-Lo Stores Com-
pany, 54 West Lake Street, Chicago,
111.
Lloyd, E. W.
General Contract Agent, Common-
wealth Edison Company, 72 West
Adams Street. Chicago, 111.
Luckiesh, M.
Physicist, Nela Research Labora-
tory, National Lamp Works of Gen-
eral Electric Company. Nela Park.
Cleveland, Ohio.
Masson, Chas. M.
Illuminating Engineer, Southern
California Edison Company, 120
East 4th Street, Los Angeles, Cal.
Moon, T. Elmer.
Consulting Engineer in Illumination,
1626 Real Estate Trust Building,
Philadelphia, Pa.
Moulton, Walter R.
Illuminating Engineer, Consolidated
Gas, Electric Light & Power Com-
pany, 325 North Charles Street. Bal-
timore. Md.
Nichols, George B.
Chief Engineer, Department of Ar-
chitecture, New York State Capitol,
Albany, N. Y.
Nutting, P. G.
Optical Engineer, Head of Physics,
Research Laboratory, Eastman
Kodak Company, Rochester, N. Y.
Ohmans. John L.
Electrician in Charge of Car Light-
ing, Chicago & Western Indiana
Railroad Company, 448 West 51st
Street, Chicago, 111.
Reeder, Charles L.
Consulting Engineer, Park Avenue
Building, Park Avenue and Sara-
toga Street, Baltimore, Md.
TRANSACTIONS I. E. S. — PART II
Rolph, T. W.
Illuminating Engineer. Ivanhoe
Metal Works of General Electric
Company, East Cleveland, Ohio.
Rowe, E. B.
Illuminating Engineer and Secre-
tary, Enterprise Electric Construc-
tion & Fixture Company, 6509
Euclid Avenue, Cleveland, Ohio.
Schmidt, Albert R.
A. R. Schmidt Electric Company.
262 East Water Street. Milwaukee.
Wis.
Scheible, Albert
Patent Attorney and Research Engi-
neer, 79 West Monroe Street, Chi-
cago, 111.
Sharp, Clayton H.
Technical Director, Electrical Test-
ing Laboratories, Inc., 80th Street
and East End Avenue, New York,
N. Y.
Spencer, W. H.
Engineer and Assistant Manager,
I. P. Frink, 239 Tenth Avenue, New
York, N. Y.
Thomas, Stephen A.
Chief, Electrical Division, Building
Bureau, Department of Education,
500 Park Avenue, New York, N. Y.
Wynne, V. C.
Consulting Engineer, 90 State Street.
Albany. N. Y.
September 23, 1915.
Adam, John N.
New Business Department, Public
Service Electric Company. 271
North Broad Street, Elizabeth.
N.J.
Allen. Harry V.
Department of Water Supply, City
of New York, 2324 Municipal Build-
ing. New York, N. ^ .
Auerbacher, Louis J.
Representative. Beck Searchlights.
120 Liberty Street. New York. N. Y.
Barrows, George S.
Engineering Department, United Gas
Improvement Company, Broad and
Arch Streets, Philadelphia, Pa.
Bartlett, P. H.
The Philadelphia Electric Company,
1000 Chestnut Street, Philadelphia,
Pa.
Benford, Frank A.. Jr.
Illuminating Engineering Labora-
tory, General Electric Company,
Dock Street. Schenectady, N. Y.
Bernhard, Frank H.
Associate Editor, Electrical Review
and Western Electrician, 608 South
Dearborn Street, Chicago. 111.
Betts, Philander
Chief Engineer, Board of Public
Utility Commissioners, 790 Broad
Street, Newark. N. J.
Bolton, Frank C.
Professor of Electrical Engineering.
Agricultural and Mechanical College
of Texas. College Station, Tex.
Bowen, Dudley A.
Westinghouse Electric & Manufac-
turing Company, 165 Broadway.
New York, N. Y.
Bronis, James
Appraiser of Unlisted Securities and
Expert Accountant for Marvyn
Scudder and The Investors' Agency.
Inc., 55 Wall Street, New York.
N. Y.
Brooks, Harold Arthur
Electrical Engineer, Potomac Elec-
tric Power Company. 231 14th Street,
N. W., Washington, D. C.
Broom, Benj. A.
Consulting Mechanical Engineer, 500
United Bank Building, Sioux City,
la.
Bryant, J. M.
Professor of Electrical Engineering.
University of Texas. Austin, Tex.
TRANSACTIONS I. E. S. — PART II
Burrows, Stephen B.
General Lighting Representative.
Public Service Electric Company.
759 Broad Street, Newark, X. J.
Cline, W. B.
President and General Manager, Los
Angeles Gas & Electric Corporation,
645 South Hill Street, Los Angeles.
Cal.
Cramptox, George S.
Ophthalmologist, 1700 Walnut Street.
Philadelphia, Pa.
Cravath, James R.
Consulting Electrical and Illumin-
ating Engineer, 140 South Dearborn
Street, Chicago. 111.
Crosby. Halsey E.
Chief Electrician. Columbia Univer-
sity, 116th Street and Amsterdam
Avenue, New York. N. Y.
Dickersox, A. F.
Illuminating Engineer, General Elec-
tric Company, Panama-Pacific Inter-
national Exposition. Service Build-
ing. San Francisco, Cal.
Dunning, Herbert S.
Westinghouse Lamp Company.
Bloomfield. X. T.
Edie, Wm. W.
Illuminating Engineer, West Perm
Electric Company, West Main
Street, Connellsville, Pa.
Edwards, Evan J.
Associate Engineer. Xational Lamp
Works of General Electric Com-
pany. Xela Park. Cleveland, Ohio.
Fuller, W. W.
Chief Engineer and Manager.
Charleston-Isle of Palms Traction
Company, Charleston Hotel Build-
ing, Charleston. S. C.
Gast, Fred W.
Mechanical - Electrical Engineer.
United States Treasury Department,
Washington, D. C.
Gross, J. Harry
Park Engineer, Board of Park Com-
missioners, Druid Hill Park, Balti-
more, Md.
Hare, Johx R.
United Gas Improvement Company,
134 West 13th Street. Philadelphia,
Pa.
Harries. George Herbert
H. M. Byllesby & Company, Union
Pacific Building, Omaha. Neb.
Hatzel, John C.
Hatzel & Buehler, 373 4th Avenue,
Xew York, X. Y.
Heilmax. Doxald B.
Mechanical and Electrical Engineer,
and Inspector, Philadelphia & Read-
ing Railway Company, Reading, Pa.
Hexxixgf.r, John G., Jr.
Salesman and Illuminating Engineer,
Fostoria Incandescent Lamp Divi-
sion, General Electric Company.
Fostoria, Ohio.
Herixg, Carl
929 Chestnut Street. Philadelphia.
Pa.
Herrick, Charles Hubbard
Xational Meter Company of New
York, 159 Franklin Street, Boston,
Mass.
Hkrzog, Johx S.
Newark Reflector Division, National
Lamp Works of General Electric
Company. Newark. Ohio.
Hibbex, S. G.
Illuminating Engineer. Macbeth-
Evans Glass Companv. Pittsburgh.
Pa.
Hicks, Leslie R.
Engineering Department, C. H.
Tenney & Company, 201 Devonshire
Street, Boston, Mass.
HrrzKER, Albert J.
Assistant Manager, Federal Minia-
ture Lamp Division, General Elec-
tric Company, 501 South Jefferson
Street, Chicago. 111.
8
TRANSACTIONS I. E. S. — PART II
Houghton, C. P.
Second Vice-President. Los Angeles
Gas & Electric Corporation, 645
South Hill Street, Los Angeles, Cal.
Humphry, George William
Sir W. G. Armstrong-Whitworth,
Ltd., 10 Sarah Street, Shielsfield,
Newcastle-on-Tyne, England.
Hyde, E. N.
Illuminating Department, Northern
Electric Company, Ltd., Post Office
Drawer 2040, Montreal, Can.
Hyde, E. P.
Director, Nela Research Laboratory,
National Lamp Works of General
Electric Company, Nela Park, Cleve-
land, Ohio.
Jackson, Dugald C.
Professor of Electrical Engineering,
Massachusetts Institute of Tech-
nology, 248 Boylston Street. Boston,
Mass.
Johnson, Lester Gurney
Commercial Engineer, General Elec-
tric Company, Schenectady, N. Y.
Jones, Loyd A.
Eastman Kodak Company, Roches-
ter, N. Y.
Jordan, Horace W.
39 Boylston Street, Boston, Mass.
Kruger, John L.
137 Grand Avenue, Brooklyn, N. Y.
Law, Clarence L.
Manager, Bureau of Illuminating
Engineering, New York Edison
Company, 130 East 15th Street, New-
York, N. Y.
Le Page, Clifford B.
Assistant Professor of Physics,
Stevens Institute of Technology,
Hoboken, N. J.
Luther, Chas. A.
Illuminating Engineer, Peoples Gas
Light & Coke Company, 122 North
Michigan Boulevard, Chicago, 111.
Magdsick. H. H.
Engineering Department, National
Lamp Works of General Electric
Company, Nela Park, Cleveland,
Ohio.
MlDDLEKAUFF, GEORGE W.
Associate Physicist, Bureau of
Standards, Washington, D. C.
Millar, Preston S.
Manager, Electrical Testing Labora-
tories, Inc., 80th Street and East
End Avenue, New York, N. Y.
Morgan, John Eyre
Superintendent Gas Plant, Paw-
tucket Gas Company, 231 Main
Street, Pawtucket, R. I.
Morgan, L. G. D.
Supervising Engineer, National
X-Ray Reflector Company, 217
Stephenson Building, Milwaukee,
Wis.
Mott. William Roy
Chemical Engineer, Research Labo-
ratory, National Carbon Company,
Corner 117th and Madison Streets,
Lakewood, Ohio.
Myer, Albert
Secretary, American Optical Asso-
ciation, 244-246 Broadway, Albert
Lea, Minn.
Neumuller, Walter
Special Representative, New York
Edison Company, 130 East 15th
Street, New York, N. Y.
Nodell, W. L.
Sub-branch Manager, Westinghouse
Lamp Company, 121 East Baltimore
Street, Baltimore, Md.
Norton, Guy Payne
Sterling Bronze Company, 16 West
40th Street, New York, N. Y.
Owens, Thurston
42 Pine Street, New York, N. Y.
TRANSACTIONS I. E. S.— PART II
Patterson, Robert B.
Superintendent, Street Lighting De-
partment, Potomac Electric Power
Company, 231 14th Street, N'. W.,
Washington, D. C.
Pope, A. A.
Assistant General Commercial Man-
ager, New York Edison Company,
130 East 15th Street, New York,
N. Y.
Radcuff, John R., Jr.
Sales Manager (Electric), Yonkers
Electric Light & Power Company,
9 Manor House Square, Yonkers,
N. Y.
RlDINGER, CHAS. W.
President, Iron City Engineering
Company, 711 Grant Street, Pitts-
burgh, Pa.
Rieha, Edward L.
Gas Engineer and Contractor, 213
Courtland Street, Baltimore, Md.
Rochester, Thomas W.
Bureau Contract Supervision, Board
of Estimate and Apportionment,
Municipal Building, New York,
N.Y.
Sawin, George A.
Illuminating Engineer, Public Ser-
vice Electric Company, 759 Broad
Street, Newark, N. J.
Schumacher, John Henry
Treasurer and Manager, Schu-
macher, Gray Company, Ltd., 386
Donald Street, Winnipeg, Manitoba,
Can.
Scofield, Thomas
Consolidated Gas Company, 130 East
15th Street, New York, N. Y.
Shaad, George C.
Professor of Electrical Engineering,
University of Kansas, Engineering
Building, University of Kansas,
Lawrence, Kan.
Shaw, Carroll H.
Electrical Engineer, Sheboygan Rail-
way & Electric Company, 1514 North
7th Street, Sheboygan, Wis.
Sheibley, Frank D.
Assistant Engineer, Consolidated
Telegraph & Electrical Subway
Company, 54 Lafayette Street, New
York, N. Y.
Silverman, Alexander
University of Pittsburgh, Pitts-
burgh, Pa.
Steadman, F. M.
Photographer, Concord, N. H.
Stark, A. W.
Engineer's Assistant, Consolidated
Gas Company of New York, 130
East 15th Street, New York, N. Y.
Steinharter, Jos J.
Vice-president, Lamp Company, The
Metalyte Company, 366 West 15th
Street, New York, N. Y.
Stevick, C. H.
Superintendent of Works, New
Amsterdam Gas Company, Ravens-
wood, Long Island City, N. Y.
Stewart, Samuel B.
General Contracting Agent, Phila-
delphia Company. 435 Sixth Avenue,
Pittsburgh, Pa.
Swallow, Joseph G.
Superintendent, Installation and In-
spection Department, United Elec-
tric Light & Power Company, 130
East 15th Street, New York, N. Y.
Tomlinson, L. C.
Electrical and Sales Engineer,
National Electric Utility Corpora-
tion, 355 West 36th Street, New
York, N. Y.
Tyler, Randolph E.
Manager, Philadelphia Office, Shelby
Lamp Division National Lamp
Works of General Electric Com-
pany, 1941 Market Street, Philadel-
phia, Pa.
10
TRANSACTIONS I. E. S. — PART II
Ware, Richard C.
Assistant to Second Vice-president.
Boston Consolidated Gas Company,
24 West Street, Boston, Mass.
Whiting, H. S.
J. Livingston & Company. 70 East
45th Street, New York, N. Y.
Weaver, W. D.
Charlottesville, Va.
Williams, Arthur
General Commercial Manager, New
York Edison Company, 130 East
15th Street, New York, N. Y.
Wilson, Frank S.
Electrical Enginer, 8 Irvington
Street, Boston, Mass.
Young, James Watts
Consulting Electrical Engineer, 58
Townsend Street, Roxbury, Mass.
October 14, 1915.
Boyce, Ernest W.
Electrical Engineer, President New
York Electric Lamp Company, Inc..
30 Park Row. New York, N. Y.
Boxell, Harold V.
Consulting Engineer and Professor
of Electrical Engineering. Univer-
sity of Oklahoma, 508 Chautauqua
Avenue, Norman. Okla.
Bull, John H.
Supervising Engineer. Ballinger &
Perrot, Marbridge Building, 34th
Street and Broadway, New York,
N. Y.
Cady, Francis E.
Assistant to Director, Nela Research
Laboratory, Nela Park, Ohio.
Carpenter, Frank
Illumination and Special Work,
Welsbach Gas Lamp Company, 392
Canal Street, New York, N. Y.
Clinch, Edward S., Jr.
Electrical Engineer, Cates & Shep-
ard, 1516 Sansom Street, Philadel-
phia, Pa.
Cowles, Joseph W.
Superintendent of Installations, Edi-
son Electric Illuminating Company
of Boston, 39 Boylston Street, Bos-
ton, Mass.
Doane, L. C.
Commercial Engineer. Holophane
Works of General Electric Com-
pany, Cleveland, Ohio.
Dodson, Herbert K.
Assistant Superintendent, New Busi-
ness and Merchandise Department,
Consolidated Gas, Electric Light &
Power Company of Baltimore, 200
West Lexington Street. Baltimore,
Md.
Doty, Paul
President and General Manager, St.
Paul Gas Light Company, 159 East
6th Street, St. Paul, Minn.
Dows, Chester L.
Electrical Engineer, National Lamp
Works of General Electric Com-
pany, Nela Park. Cleveland, Ohio.
Dutton, L. R.
Manager. Philadelphia Suburban
Gas & Electric Company, Wyncote.
Pa.
Gaxz. Albert Frederick
Consulting Engineer and Professor
of Electrical Engineering, Stevens
Institute of Technology, Hoboken.
X. J.
Hanscom, W. W.
Consulting Engineer, 848 Clayton
Street, San Francisco, Cal.
Hess, William L.
Oculist, 400 California Building,
Denver, Colo.
Holdrege. H. A.
General Manager, Omaha Electric
Light & Power Company, Omaha,
Neb.
Hulse, Geo. E.
Chief Engineer, Safety Car Heating
& Lighting Company, 2 Rector
Street, New York. N. Y.
TRANSACTIONS I. H. S. —PART II
11
Jackson, Dugald C.
Professor of Electrical Engineering,
Massachusetts Institute of Technol-
ogy, 248 Boylston Street, Boston.
Mass.
Keech, George C.
District Sales Manager, Cooper-
Hewitt Electric Company, 215 Fisher
Building, Chicago, 111.
Kellogg, Alfred S.
Consulting Engineer, 53 State Street,
Boston, Mass.
Kennedy, Geo. M.
Electrical Engineer, Lehigh Coal &
Navigation Company, no East
Ridge Street, Lansford, Pa.
Kingsbury, E. F.
Research Assistant, United Gas Im-
provement Company, Physical Lab-
oratory, 3101 Passyunk Avenue,
Philadelphia, Pa.
Magalhaes, George W.
Assistant to the President, New
York & Queens Electric Light &
Power Company, 444 Jackson Ave-
nue, Long Island City, N. Y.
Marsh, Loren W.
New England Manager, American
Luxfer Prism Company, 49 Federal
Street, Boston, Mass.
Mixer, Chas. A.
Engineer, Rum ford Falls Light &
Water Company, 49 Congress Street,
Rumford, Me.
Morton, F. N.
Engineer, United Gas Improvement
Company, Broad & Arch Streets,
Philadelphia, Pa.
Nicolai, G. O.
Superintendent, Light & Power De-
partment, Terre Haute I. & E.
Traction Company, 820 Wabash
Avenue, Terre Haute, Ind.
O'Leary, J.J.
President, Buffalo Electric Contract-
ing Company, 20 Broadway, Buffalo,
N. Y.
i'l'ASLEE, W. Dhu Aine
Consulting Engineer, also Lecturer
in Electrical Engineering, Oregon
Agricultural College, Corvallis, Ore.
Porter, Lawrence C.
Illuminating Engineer, Edison Lamp
Works of General Electric Com-
pany, 417 Sussex Street, Harrison,
N. J.
Clover, Geo. R.
District Manager, Cooper-Hewitt
Electric Company, 427 Ford Build-
ing, Detroit, Mich.
Rose, S. L. E.
Illuminating Engineering Labora-
tory, General Electric Company,
Schenectady, N. Y.
Ryan, Walter D'Arcy
Director of Illuminating Engineer-
ing Laboratories, General Electric
Company, Schenectady. N. Y.
Simpson, Richard E.
Engineer, Travelers' Insurance Com-
pany, 700 Main Street, Hartford,
Conn.
Tingley, Dr. Louisa Paine
Ophthalmologist, 9 Massachusetts
Avenue, Boston, Mass.
Treverton, E. R.
Lighting Engineering Service Com-
pany and Lighting Journal, 241
West 37th Street, New York, N. Y.
Wohlauer, A. A.
Consulting Engineer, Allied Engi-
neering Company, 546 Fifth Avenue,
New York, N. Y.
Murphy, John
Electrical Engineer, Government of
Canada, Department Railways and
Canals, Ottawa, Can.
TRANSACTIONS
OF THE
Illuminating
Engineering Society
NO. 8, 1915
PART II
Miscellaneous Notes
16
TRANSACTIONS I. E. S. — PART II
Council Notes.
A regular meeting of the Council was
held in the general offices of the society,
29 West 39th Street, New York, Octo-
ber 14, 1915. Those present were:
Charles P. Steinmetz, president ; H.
Calvert, \Ym. A. Durgin, Clarence L.
Law, M. Luckiesh, A. S. McAllister,
L. B. Marks, treasurer ; J. Arnold Nor-
cross, and G. H. Stickney.
The minutes of the June 10 meeting
were adopted as printed.
The Council Executive Committee
presented the following report giving a
summary of its activities on behalf of
the Council during the summer months :
Since the last meeting of the Council in June,
the Council Executive Committee has:
(1) Held three meetings, August 5, August
18 and September 23, 1915.
(2) Authorized the payment of vouchers
Nos. 2136-2138, 2167-2256 inclusive aggregating
$2,461.82.
(3) Elected 23 associate members and 2 sus-
taining members.
(4) Accepted the resignations of 34 associate
members.
(5) Transferred 123 associate members to
the grade of member.
The report was adopted.
Six applicants were elected associate
members.
Twenty-one associate members were
transferred to the grade of member.
Upon recommendation of the Finance
Committee, payment of vouchers No.
2257 to No. 2278 inclusive aggregating
$1,250.28 was authorized.
Reports were given by Mr. G. H.
Stickney, former vice-president of the
New York Section; Mr. H. Calvert for
Geo. A. Hoadley, vice-president of the
Philadelphia Section, and Mr. L. B.
Marks, chairman of the Committee on
Lighting Legislation.
The following committee appoint-
ments were confirmed :
Finance: H. Calvert, chairman; J. A.
Norcross, P. S. Young.
Papers: G H. Stickney, chairman ;
A. S. McAllister, YV. F. Little, G. W.
Roosa, L. B. Marks, and the chairmen
of section Papers Committees.
Editing and Publication: C. H.
Sharp, chairman ; Norman Macbeth,
M. G. Lloyd.
Membership: Douglass Burnett, chair-
man; A. L Abbott, J. J. Burns, W. R.
Collier, S. L. E. Rose, A. M. Wilson,
R E. Simpson, T. M. Ambler, J. C.
McLaughlin, and the chairmen of the
section Membership Committees.
Sustaining Membership: W. M. Skiff,
chairman; S. G. Hibben, E. W. Lloyd,
E. B. McLean, S. L. E. Rose, E. B.
Rowe.
Popular Lectures: E. J. Edwards,
chairman; A. J. Rowland, vice-chair-
man.
a — Sub-committee on Residence
Lighting: E. J. Edwards, chairman,
b — Sub-committee on Industrial
Lighting: W. A. D. Evans, chair-
man; R. ff. Pierce.
c — Sub-committee on Elementary
Lecture: W. S. Franklin, chairman.
d — Sub-committee on Store Light-
ing: A. L. Powell, chairman.
e — Sub-committee on Office Light-
ing: C. E. Clewell, chairman.
Lighting Legislation: L. B. Marks,
chairman; O. H. Basquin, C. E. Clewell,
Oscar H. Fogg, Clarence L. Law, M.
Luckiesh, F. J. Miller, G. H. Stickney,
L. H. Tanzer, W. H. Tolman, C. 6.
Bond, and F. A. Vaughn.
Glare: P. G. Nutting, chairman;
Nelson M. Black, J. R. Cravath, F. H.
Gilpin, M. Luckiesh, F. K. Richtmyer,
F. A. Vaughn.
Progress: F. E. Cady, chairman;
Walter B. Lancaster, T. J. Litle, Jr.,
L. B. Marks, F. N. Morton, T. W.
Rolph.
TRANSACTIONS I. E. S. — PART II
Section Development: General Sec-
retary, chairman ; section secretaries.
Council Executive Committee: Chas.
P. Steinmetz, chairman; L. B. Marks,
H. Calvert.
Reciprocal Relations: W. J. Serrill,
chairman; F. Park Lewis, F. E. Wallis,
chairmen of sections, G. H. Stickney,
C. H. Sharp.
Advertising: M. C. Turpin, chair-
man; J. C. McQuiston, Joseph D. Israel.
Nomenclature and Standards: A. E.
Kennelly, chairman; C. H. Sharp, secre-
tary; Louis Bell, C. O. Bond, S. E.
Doane, W. A. Dorey, E. P. Hyde, C. O.
Mailloux, A. S. Miller, P. G. Nutting,
E. B. Rosa, W. E. Saunders.
Research: E. B. Rosa, chairman;
P. W. Cobb, G. W. Middlekauff, P. G.
Nutting, F. K. Richtmyer, C. H. Sharp,
E. C. Crittenden, C. E. Ferree, E. P.
Hyde, E. F. Kingsbury, Preston S.
Millar, W. E. Wickenden, H. E. Ives.
It was decided to hold a semi-annual
convention early in February to cele-
brate the ioth anniversary of the organ-
ization of the society.
After a discussion of the proposal to
arrange for a course of lectures, similar
to those presented at the Johns Hopkins
University in the fall of 1910, to be
given in the fall of 1916 under the
auspices of the society, it was moved
and carried that President Steinmetz be
authorized to make such preparations
as he deems desirable for the lecture
course.
Thereupon the following committee
appointments were confirmed, subject to
changes :
a — Committee on Ways and Means:
Preston S. Millar, chairman.
b— Committee on Lectures: L. B.
Marks, chairman.
The resignation of Mr. Alten S.
Miller, general secretary, was accepted.
It was moved and carried that the
assistant secretary write Mr. A. S.
Miller that the Council hopes he will
retain his seat as a director.
A regular meeting of the Council
was held in the offices of the society,
November 11, 1915- Those present
were: Charles P. Steinmetz, presi-
dent; E. M. Alger, H. Calvert, G. A.
Hoadley, Clarence L. Law, A. S.
McAllister, J. L. Minick, L. B. Marks,
C. O. Bond. Upon invitation: C. E.
Clewell, G. H. Stickney.
The minutes of the October meeting
were read, but adoption was postponed
until they shall have appeared in print.
Nine applicants were elected associate
members of the society.
Four applicants were elected sustain-
ing members.
Thirty-eight associate members were
transferred to the grade of member.
Upon recommendation of the Finance
Committee, vouchers No. 2279 to No.
2316 inclusive aggregating $1,833.62
were authorized paid subject to the
approval of the general secretary.
A report recommending certain rules
of procedure with regard to the publi-
cation of papers and discussions was
received from the Committee on Editing
and Publication. Thereupon the ques-
tion of the use of trade, firm, individual
and corporate names in the publications
of the society was raised for discussion.
It was voted that the Committee on
Editing and Publication be asked to
draft some definite policy on this matter
to be submitted at an early date, with the
aforementioned rules, for the approval
of the Council. It was understood that
the members of the Council would be
asked individually to communicate their
views on the question to the committee.
TRANSACTIONS I. E. S. PART II
The following committee appoint-
ments were confirmed :
Reciprocal Relations: Dr. E. M.
Alger, chairman.
School Lighting: M. Luckiesh, chair-
man.
Lighting Legislation: C. E. Stephens.
Semi- Annual Convention: Arthur
Williams, chairman.
Board of Examiners: A. S. McAllis-
ter, chairman; W. Cullen Morris,
Bassett Jones.
It was voted that chairmen of com-
mittees who serve on other committees
be listed, on the latter committees, as
co-operating members.
The resignation of Mr. A. S. Miller
as a director was accepted with a vote
of thanks from the Council for services
rendered.
Mr. C. A. Littlefield was appointed
general secretary to succeed Mr. Alten
S. Miller, resigned.
Mr. Preston S. Millar was appointed
a director to succeed Mr. Alten S.
Miller, resigned.
Mr. J. L. Minick was appointed a
delegate of the society to attend the
exercises of the Carnegie Institute of
Technology in celebration of the eigh-
tieth birthday of Mr. Carnegie and the
tenth anniversary of the founding of
the Institute, to be held in Pittsburgh,
Pa., November 23, 24, 1915.
Reports on section activities were re-
ceived from Vice-presidents G. A.
Hoadley and C. L. Law.
The question of time and place for
giving the lectures on illuminating engi-
neering was discussed informally. Mr.
Clewell said that he thought the Uni-
versity of Pennsylvania would invite the
society to give the lectures at the U.
of P.
It was suggested that a design for a
new membership certificate be drawn up
and submitted for the approval of the
Council.
It was decided to make the official
badges of the society in the following
colors : blue background for members ;
maroon for associate members, and
white for honorary members.
The question was raised whether it
would be desirable to draft a specifica-
tion or statement of some kind for pho-
tographs and lantern slides showing
comparative illuminated views which are
used to illustrate papers given before
the society. It was pointed out that
these pictures are often misleading
because of the absence of information
regarding the conditions under which
they are made. It was voted to refer
this question to the Committee on
Research.
New Associate Members.
At the October 14th meeting of the
Council, the following six applicants
were elected to associate membership :
Graff, Weseey M. (Ph.B., M. E.)
Consulting Engineer, Graves Engi-
neering Co., Inc., 35 Pine St., New
York, N. Y.
Newun, E. M.
Agent, New York Edison Co.,
Irving Place and 15th St., New
York, N. Y.
Newton, Arthur Hazeett
Electrical Engineer, Bureau of Pub-
lic Works, Manila, P. I.
O'Shea, James P.
General Sales Agent, Cooper-Hewitt
Electric Co., 730 Grand St.,
Hoboken, N. J.
Robnett, Edwin H.
Representative, Westinghouse Elec-
tric & Manufacturing Co., 121 East
Baltimore St., Baltimore, Md.
TRANSACTIONS I. E. S. — PART II
SCHERESCHEWSKY, J. W.
Surgeon, U. S. Public Health Ser-
vice, U. S. Marine Hospital, Pitts-
burgh, Pa.
At the meeting of the Council held
November n, the following nine appli-
cants were elected associate members :
Brandreth, Guy S.
Lighting Service Department, Phila-
delphia Electric Co., iooo Chestnut
St., Philadelphia, Pa.
Carder, Frederick
Vice-president and General Man-
ager, Steuben Glass Works, Corn-
ing, N. Y.
Hughes, David M.
Photometric Testing, Electrical
Testing Laboratories, 8oth St. and
East End Ave., New York, N. Y.
Markley, Ralph E.
Lighting Service Department, Phila-
delphia Electric Co., iooo Chestnut
St., Philadelphia, Pa.
Murray, Joseph Bradley
Acting Treasurer, Edison Electric
Illuminating Co. of Brooklyn, 360
Pearl St., Brooklyn, N. Y.
Pearsall, George Martin
Assistant in Physics, Cornell Uni-
versity, 415 North Cayuga St.,
Ithaca, N. Y.
PlNCKLEY, W. F. T.
Newcastle Electric Supply Co.,
Hood St., Newcastle-on-Tyne, Eng-
land.
Rein, Frederick E.
Business Engineer and Public
Accountant, Frederick Rein & Staff,
1201 Chestnut St., Philadelphia, Pa.
Koehler, William F.
Philadelphia Electric Co., 226 South
nth St., Philadelphia, Pa.
Section Meetings.
Chicago Section
November 4, 1915, in the Common-
wealth Edison Company Building.
Paper, "Semi-indirect Office Lighting in
the Edison Building of Chicago" by
Messrs. W. A. Durgin and J. B. Jack-
son. Attendance 250.
The following program of papers and
meetings has been announced :
December 9 — School Lighting.
January 13 — Exterior Lighting (Gas
and Electric) of Buildings.
February 10 — Practical Factor}^ Light-
ing.
February 28 — Joint meeting of Chi-
cago sections of A. I. E. E. and I. E. S.
Paper on street lighting.
March 23 — Latest Developments in
Incandescent Lamps.
April 20 — Latest Developments in Gas
Lamps.
May 18 — Relation of Illumination to
Interior Architectural Effects.
June 15— Modern Reflectors and
Shades for Gas and Electric Lighting.
The names of the authors of these
papers will be announced later.
New England Section
The first meeting of the section this
year is to be held in February, 1916. A
definite announcement will be made
later.
New York Section
November 15, 1915. Joint meeting
with American Electrochemical Society
in Engineering Societies Building.
Papers: (1) "Unstable States in the
Arc and Glow" by Walter G. Cady of
Wesleyan University, Middletown, Conn.
(2) "Gaseous Conductor Light" by D.
McFarlan Moore, Harrison, N. J. (3)
"Electric Arc in Complex Vapors at
TRANSACTIONS I. E. S.— PART II
Reduced Pressures" by W. A. Darrah,
Mansfield, O.
The following meetings have been
announced :
December 8, 1915 — Papers: (1) Prog-
ress in Home Lighting by Gas" by
Thomas Scofield; (2) "Commercial
Aspects of Gas Lighting" by Charles
Hodgson.
January 13, 1916 — Papers: (1) "Light
Transmission in Optical Instruments"
by Dr. F. L. G. Kollmorgen; (2 "Pro-
jector Lamps" by Mr. Orange of the
General Electric Company.
March 9, 1916 — Joint meeting with
American Society of Mechanical Engi-
neers : Paper by Prof. C. E. Clewell
of the University of Pennsylvania on
"Application of the New Factory Code."
April 13, 1916 — A lecture by Dr.
Charles P. Steinmetz, president of the
Illuminating Engineering Society, on
"Illuminating Engineering."
May 11, 1916 — Papers: "Street Light-
ing" by S. G. Rhodes ; "Office Lighting"
by Bassett Jones ; "Stage Lighting" by
David Belasco.
Philadelphia Section
November 19, 1915, Engineers' Club,
1317 Spruce Street. Paper : "Coal
Mine Illumination ; its Relation to Acci-
dent Prevention and Miners' Nystac-
mus" by R. E. Simpson. Attendance 33.
The program for the rest of the year
is as follows :
December 17 — Joint meeting with
Engineers' Club. "Illuminating Engi-
neering," by Charles P. Steinmetz,
A. M., Ph. D., President, Illuminating
Engineering Society; Chief Consulting
Engineer, General Electric Company.
January 21 — "Illumination Problems
at the Panama-Pacific Exposition," by
W. D'A. Ryan, Illuminating Engineer,
General Electric Company.
February 18 — "Tests of Street Illumi-
nation," by Preston S. Millar, Past-
president, Illuminating Engineering
Society; General Manager, Electrical
Testing Laboratories.
March 13 — Joint meeting with Phila-
delphia Section, American Institute of
Electrical Engineers. "Engineering
Training as a Business Assett," by
Charles F. Scott, Sc. D., Past-president,
American Institute of Electrical Engi-
neers; Professor of Electrical Engineer-
ing, Sheffield Scientific School of Yale
University.
March 17 — "Lighting Legislation," by
L. B. Marks, Past-president, Illuminat-
ing Engineering Society; Consulting
Engineer.
April 21 — "Type C Lamps in Street
Lighting," by T. J. Pace, Commercial
Engineer, Westinghouse Electric &
Manufacturing Company.
May 19 — "Educational Aspects of
Illumination," by Prof. F. K. Richt-
myer, Chairman, Committee on Educa-
tion, Illuminating Engineering Society.
June 16— "Artificial Lighting for a
Hundred Years," by William J. Serrill,
Engineer of Distribution, United Gas
Improvement Company.
Pittsburgh Section
November 19, 1915. Educational
meeting in Science Building, Carnegie
Institute of Technology. Papers: (1)
"Can Light be Measured?" by G. W.
Roosa; (2) "Instruments that are Used
in Measuring the Quantity of Light" by
H. H. Magdsick; (3) "Instruments that
are Used in Measuring Quality of
Light" by Dr. L. O. Grondahl.
TRANSACTIONS I. E. S. — PART II
Transfers.
The following twenty-one applicants
were transferred from the grade' of
associate member to that of member at
a meeting of the Council held October
14, 1915:
Arenberg, Albert L.
Illuminating Engineer, Central Elec-
tric Co., 320 South 5th Ave., Chi-
cago, 111.
Brady, Edward J.
Physical Laboratory, United Gas
Improvement Co., 3101 Passyunk
Ave., Philadelphia, Pa.
Clark, Emerson L.
Physicist, National Carbon Co.,
Cleveland, O.
Eichengreen, L. B.
Gas Engineer, Manufacturer and
Distributor of Gas, 1401 Arch St.,
Philadelphia, Pa.
Gartley, William H.
Vice-president, Equitable Illuminat-
ing Gas Light Co., 1401 Arch St.,
Philadelphia, Pa.
Gilpin, Francis H.
Gas Engineer, United Gas Improve-
ment Co., 3101 Passyunk Ave.,
Philadelphia, Pa.
Ives, Herbert E.
Physicist, United Gas Improvement
Co., 3101 Passyunk Ave., Philadel-
phia, Pa.
Jordan, C. W.
Assistant, Physical Laboratory,
United Gas Improvement Co., 3101
Passyunk Ave., Philadelphia, Pa.
Kelly, J. B.
Salesman, Illuminating Department,
Frank H. Stewart Electric Co., 37
North 7th St., Philadelphia, Pa.
Kiefer, Lewis J.
Building Superintendent, McCreery
& Co., Sixth Ave. and Wood St.,
Pittsburgh, Pa.
Little, William F.
Engineer in Charge of Photometry,
Electrical Testing Laboratories, 80th
St. and East End Ave., New York,
N. Y.
Macdonald, Norman D.
Assistant to Manager, Electrical
Testing Laboratories, 80th St. and
East End Ave., New York, N. Y.
Palmer, H. C.
Engineer, Buffalo Gas Co., 186 Main
St., Buffalo, N. Y.
Pierce, Robert ff.
Manager, Illuminating Engineering
Laboratory, Welsbach Co., Glouces-
ter, N. J.
Rogers, Fred. A.
Professor of Physics and Electrical
Engineering, Lewis Institute, Chi-
cago, 111.
Serrill, William J.
Engineer of Distribution, United
Gas Improvement Co., 1401 Arch
St., Philadelphia, Pa.
Sxyder, Samuel
Illuminating Specialist, New Busi-
ness Department, The United Gas
Improvement Co., 134 North 13th
St., Philadelphia, Pa.
Spencer, Paul
Electrical Engineer, United Gas
Improvement Co., 1401 Arch St.,
Philadelphia, Pa.
Morton, A. A.
Westinghouse Electric & Manufac-
turing Co., Union Bank Bldg., Pitts-
burgh, Pa.
Dicker, Alfred Osmond
Illuminating Engineer, Electrical
Sales Engineers, Inc., 19 South
Fifth Ave., Chicago, 111.
Rice, Harry C.
General Manager, G. I. Lamp Divi-
sion, National Lamp Works of
General Electric Co., 214 Electric
Bldg., Cleveland, O.
8
TRANSACTIONS I. E. S. — PART II
The following thirty-eight associate
members were transferred to the grade
of member November n, 1915 :
Boyce, Ernest W.
Electrical Engineer, President New
York Electric Lamp Co., Inc., 38
Park Row, New York, N. Y.
Boxell, Harold V.
Consulting Engineer and Professor
of Electrical Engineering, Univer-
sity of Oklahoma, 508 Chautauqua
Ave., Norman, Okla.
Bull, John H.
Supervising Engineer, Ballinger &
Perrott, Marbridge Bldg., 34th St.
and Broadway, New York, N. Y.
Cady, Francis E.
Assistant to director, Nela Research
Laboratory, Nela Park, O.
Carpenter, Frank
Illumination and special work,
Welsbach Gas Lamp Co., 392 Canal
St., New York, N. Y.
Ceinch, Edward S., Jr.
Electrical Engineer, Gates & Shep-
ard, 1516 Sansom St., Philadelphia,
Pa.
Cowees, Joseph W.
Superintendent of Installations,
Edison Electric Illuminating Co. of
Boston, 29 Boylston St., Boston,
Mass.
Doane, L. C.
Commercial Engineer, Holophane
Works of General Electric Co.,
Holophane Works, Cleveland, O.
Dodson, Herbert K.
Assistant Superintendent, New
Business and Merchandise Depart-
ment, Consolidated Gas, Electric
Light & Power Co. of Baltimore,
200 W. Lexington St., Baltimore,
Md.
Doty, Paul
President and General Manager,
St. Paul Gas Light Co., 159 East
6th St., St. Paul, Minn.
Dows, Chester L.
Electrical Engineer, National Lamp
Works of General Electric Co.,
Nela Park, Cleveland, O.
Dutton, I. R.
Manager, Philadelphia Suburban
Gas & Electric Co., Wyncote, Pa.
Ganz, Albert Frederick
Consulting Engineer and Professor
of Electrical Engineering, Stevens
Institute of Technology, Hoboken,
N. J.
Hanscom, W. W.
Consulting Engineer, 848 Clayton
St., San Francisco, Cal.
Holdrege, H. A.
General Manager, Omaha Electric
Light & Power Co., Omaha, Neb.
Hulse, Geo. E.
Chief Engineer, Safety Car Heating
& Lighting Co., 2 Rector St., New
York, N. Y.
Jackson, Dugald C.
Professor of Electrical Engineer-
ing, Massachusetts Institute of
Technology, 248 Boylston St., Bos-
ton, Mass.
Keech, George C.
District Sales Manager, Cooper-
Hewitt Electric Co., 215 Fisher
Bldg., Chicago, 111.
Kellogg, Alfred S.
Consulting Engineer, 53 State St.,
Boston, Mass.
Kennedy, Geo. M.
Electrical Engineer, Lehigh Coal &
Navigation Co., no E. Ridge St.,
Lansford, Pa.
Kingsbury, E. F.
Research Assistant, United Gas
Improvement Co., Physical Labora-
tory, 3101 Passyunk Ave., Philadel-
phia, Pa.
TRANSACTIONS I. E. S. — PART II
Magalhaes, George W.
Assistant to the President, New
York & Queens Electric Light &
Power Co., 444 Jackson Ave., Long
Island City, N. Y.
Marsh, Loren W.
New England Manager, American
Luxter Prism Co., 49 Federal St.,
Boston, Mass.
Mixer, Chas. A.
Engineer, Rumford Falls Light &
Water Co., 49 Congress St., Rum-
ford, Me.
Morton, F. N.
Engineer, United Gas Improvement
Co., Broad and Arch Sts., Philadel-
phia, Pa.
Nicolai, G. O.
Superintendent, Light and Power
Dept., Terre Haute I. & E. Traction
Co., 80 Wabash Ave., Terre Haute,
Ind.
O'Leary, J. J.
President, Buffalo Electric Con-
tracting Co., 20 Broadway, Buffalo,
N. Y.
Peaslee, W. Dhu Aine
Consulting Engineer, also Lecturer
in Electrical Engineering, Oregon
Agricultural College, Corvallis, Ore.
Porter, Lawrence C.
Illuminating Engineer, Edison Lamp
Works of General Electric Co., 417
Sussex St., Harrison, N. J.
Clover, Geo. R.
District Manager, Cooper-Hewitt
Electric Co., 427 Ford Bldg., Detroit,
Mich.
Rose, S. L E.
Illuminating Engineering Labora-
tory, General Electric Co., Schenec-
tady, N. Y.
Ryan, Walter DArcy
Director of Illuminating Engineer-
ing Laboratories, General Electric
Co., Schenectady, N. Y.
Simpson, Richard E.
Engineer, Travelers Insurance Co.,
700 Main St., Hartford, Conn.
Tingley, Dr. Louisa Paine
Ophthalmologist, 9 Massachusetts
Ave., Boston, Mass.
Treverton, E. R.
Lighting Journal, 241 West 37th St.,
New York, N. Y.
Wohlauer, A. A.
Consulting Engineer, Allied Engi-
neering Co., 546 Fifth Ave., New
York, N. Y.
Murphy, John
Electrical Engineer, Government of
Canada, Department of Railways
and Canals, Ottawa, Canada.
New Sustaining Members.
The following companies were elected
sustaining members of the society at a
meeting of the Council held November
11, 1915:
Malden and Melrose Gas Light Co.
Clifford E. Paige, representative,
137 Pleasant St., Maiden, Mass.
Suburban Gas & Electric Co.
C. F. Chisholm, representative, 150
Beach St., Revere, Mass.
Haverhill Electric Co.
F. L. Ball, representative, 121 Mer-
rimack St., Haverhill, Mass.
Personals.
Mr. Ray Palmer, formerly commis-
sioner of electricity for the City of
Chicago, assumed the office of vice-
president and general manager of the
New York and Queens Electric Light
and Power Company, Long Island City,
N. Y., November i, 1915.
Mr. S. G. Hibben, who has been con-
nected with the Macbeth-Evans Glass
Company for a number of years, is now
10
TRANSACTIONS I. E. S. — PART II
with the National Lighting Products
Company, Jenkins Arcade, Pittsburgh,
Pa.
Air. L. L. Hopkins, formerly with the
Macbeth- Evans Glass Company, is now
the Pittsburgh representative of the
R. U. V. Company, Inc., 50 Broad
Street, New York. His office is in the
Magee Building, Pittsburgh, Pa.
Obituary.
Mr. E. S. Marlow, manager of the
commercial department of the Potomac
Electric Power Company, Washington,
D. C, died October 25 after an illness
of several months. Mr. Marlow was
widely known in the central station field
and had been active in the affairs of
the Illuminating Engineering Society
since its inception. Pie was chairman
of the committee which had charge of
the 1915 convention of the society in
Washington, D. C.
Semi-Annuai Convention.
A special semi-annual convention will
be held in New York, February 10 and
11, 1916, to celebrate the tenth anniver-
sary of the organization of the society.
A detailed announcement will be issued
later.
TRANSACTIONS
OF THE
Illuminating
Engineering Society
NO. 9, 1915
PART II
Miscellaneous Notes
TRANSACTIONS I. E. S. — PART II
Council Notes.
Date: December 9, 1915.
Place : General Offices, 29 West 39th
Street, New York, N. Y.
Present : Charles P. Steinmetz, presi-
dent ; E. M. Alger, C. O. Bond, H. Cal-
vert, G. A. Hoadley, Clarence L. Law,
C. A. Littlefield, L. B. Marks, Preston
S. Millar, J. L. Minick, A. S. McAllister,
J. Arnold Norcross, and S. C. Rogers,
representing C. A. B. Halvorson.
The meeting was called to order at
2.55 p.m. by President Steinmetz.
The minutes of the October and
November meetings were adopted as
printed.
Six applicants were elected associate
members.
One applicant was elected a member
subject to the approval of the Board of
Examiners.
Two companies were elected sustain-
ing members.
Eleven associate members were trans-
ferred to the grade of member .
Sixty-three resignations were ac-
cepted.
It was voted to have the general office
continue the occupancy of the present
quarters in the Engineering Societies
Building, New York.
Upon recommendation of the Finance
Committee, payment of vouchers No.
2317 to No. 2349 inclusive aggregating
$1,085.37 was authorized.
An estimate of the expenses and in-
come for the present fiscal year was
submitted by the Finance Committee,
but no action was taken on it.
Reports on section activities were
submitted by Vice-presidents J. L.
Minick (Pittsburgh), G. A. Hoadley
(Philadelphia), Clarence L. Law (New
York). Mr. S. C. Rogers reported on
the New England Section activities for
Vice-president C. A. B. Halvorson.
The following committee appoint-
ments were confirmed :
Committee on Lectures: E. P. Hyde,
chairman; Louis Bell, W. H. Gartley,
L. B. Marks, C. H. Sharp, and W. D.
Weaver.
Membership Committee: W. A. Dur-
gin, chairman.
School Lighting Committee: F. Park
Lewis, F. K. Richtmyer, L. O. Grondahl,
N. M. Black, H. H. Magdsick, R. B.
Ely.
Executive Committee: Preston S.
Millar.
Semi-annual Convention Committee:
Walter R Addicks, William H. Bradley,
N. F. Brady, A. W. Burchard, Nicholas
Murray Butler, J. J. Carty, Charles A.
Coffin, Geo. B. Cortelyou, Wilbur C.
Fisk, Lewis B. Gawtry, Frank Hedley,
W. Greeley Hoyt, A. C. Humphreys,
M. R Hutchison, J. W. Lieb, T. C.
Martin, Wm. H. Meadowcroft, H. B.
McLean, Joseph B. Murray, Thomas E.
Murray, Walter Newmuller, L. A.
Osborne, Geo. F. Parker, J. E. Phillips,
Theodore P. Shonts, Frank W. Smith,
B. W. Stilwell, C. G. M. Thomas, G. E.
Tripp, W. F. Wells, Frederick Whit-
ridge, Timothy S. Williams, William
Williams, Clarence L. Law, secretary.
A letter was received from the pro-
vost of the University of Pennsylvania
inviting the society to give its proposed
course of lectures on illuminating engi-
neering at the U. of P. This invitation
was referred to the Committee on Ways
and Means.
TRANSACTIONS I. E. S. — PART II
Section Meetings.
Chicago Section
December 9, 1915, in the Common-
wealth Edison Company Building.
Paper, "School Lighting" by M.
Luckiesh. Preceding the meeting sup-
per was served at the Grand Pacific
Hotel.
The following program of papers and
meetings have been announced:
January 13— Exterior Lighting (Gas
and Electric) of Buildings.
February 10 — Practical Factory Light-
ing.
February 28 — Joint meeting of Chi-
cago sections of A. I. E. E. and I. E. S.
Paper on street lighting.
March 23— Latest Developments in
Incandescent Lamps.
April 20 — Latest Developments in Gas
Lamps.
May 18 — Relation of Illumination to
Interior Architectural Effects.
June 15 — Modern Reflectors and
Shades for Gas and Electric Lighting.
The names of the authors of these
papers will be announced later.
New England Section
The first meeting of the section this
year is to be held in February, 1916.
A definite announcement will be made
later.
New York Section
December 8, 1915, in Consolidated Gas
Company's auditorium, 130 East 15th
Street, New York, N. Y. Papers, "Out-
door Illumination of Store Fronts" by
Charles Hodgson, and "Residence Light-
ing by Gas" by M. A. Combs. Preced-
ing the meeting an informal and an a la
carte dinner was held at Likhow's Res-
taurant.
The following meetings and papers
have been announced :
January 13 — A paper will be presented
by Mr. Kollmorgen of the Eastern
Optical Company, entitled "Light Trans-
mission in Optical Instruments" and
also a paper by Mr. Orange of the
General Electric Company, entitled
"Projector Lamps."
By motion of the Board, the February
meeting has been canceled in favor of
the mid-winter convention.
March 14 — Joint meeting with Ameri-
can Society of Mechanical Engineers.
A paper will be presented by Prof. C.
E. Clewell of the University of Pennsyl-
vania entitled "Application of the New
Factory Code Lighting." Talks will
also be given by Mr. L. B. Marks and
a member of the A. S. M. E.
April 13 — A lecture by Dr. Charles P.
Steinmetz on "Illuminating Engineer-
ing."
May 11 — A paper will be presented
by Mr. Bassett Jones, entitled "Office
Lighting."
June — A paper will be presented by
Mr. Wm. Dempsey of the New York
Edison Company, entitled "Street Light-
ing with Mazda C Lamps."
It is proposed to have the June meet-
ing an outdoor meeting to include a
dinner and an inspection trip through
the streets of New York.
Philadelphia Section
December 17, 1915, in Engineers Club,
joint meeting with Engineers Club and
American Institute of Electrical Engi-
neers. Dr. Charles P. Steinmetz
addressed the members on the subject
of "Illuminating Engineering."
The program for the rest of the year
is as follows :
January 21 — "Illumination Problems
at the Panama-Pacific Exposition," by
TRANSACTIONS I. E. S. PART II
W. D'A. Ryan, Illuminating Engineer,
General Electric Company.
February 18 — "Tests of Street Illumi-
nation," by Preston S. Millar, Past-
president, Illuminating Engineering
Society; General Manager, Electrical
Testing Laboratories.
March 13 — Joint meeting with Phila-
delphia Section, American Institute of
Electrical Engineers. "Engineering
Training as a Business Asset," by
Charles F. Scott, Sc. D., Past-president,
American Institute of Electrical Engi-
neers ; Professor of Electrical Engineer-
ing, Sheffield Scientific School of Yale
University.
March 17 — "Lighting Legislation," by
L. B. Marks, Past-president, Illuminat-
ing Engineering Society; Consulting
Engineer.
April 21 — "Type C Lamps in Street
Lighting," by T. J. Pace, Commercial
Engineer, Westinghouse Electric &
Manufacturing Company.
May 19 — "Educational Aspects of
Illumination," by Prof. F. K. Richt-
myer, Chairman, Committee on Educa-
tion, Illuminating Engineering Society.
June 16 — "Artificial Lighting for a
Hundred Years," by William J. Serrill,
Engineer of Distribution, United Gas
Improvement Company.
Pittsburgh Section
December 17, 1915, at Engineers'
Society of Western Pennsylvania.
Paper, "Design and Manufacture of
Diffusing Glass Reflectors" by S. G.
Hibben. An a la carte dinner was held
at the Fort Pitt Hotel.
New Associate Members.
The following six applicants were
elected associate members at a Coun-
cil meeting held December 9, 1915 :
Babson, A. C.
Watertown Manager, Wisconsin
Gas & Electric Co., 205 Main St.,
Watertown, Wis.
Housekeeper, William G
Electrical Engineer, Western Elec-
tric Co., 463 West St., New York,
N. Y.
Marlow, S. L.
Salesman, Philadelphia Electric Co.,
1000 Chestnut St., Philadelphia, Pa.
OSHIMA, HIRO-YOSHI
Osaka Electric Lamp Co., 70 Daini,
Sagisu-cho, Osaka, Japan.
Ruth, Robert H.
Benjamin Electric Manufacturing
Co., Pittsburgh, Pa.
Spillan, James J.
Laboratory assistant, Philadelphia
Electric Co., 226 S. nth St., Phila-
delphia, Pa.
New Sustaining Members.
The following companies were elected
sustaining members of the society at a
Council meeting held December 9, 1915 :
American Optical Co.
Southbridge, Mass. Official Repre-
sentative, Howard T. Reeve.
Malden Electric Co.
Maiden, Mass. Official Representa-
tive, Cyrus Barnes.
Transfers.
Eleven associate members were trans-
ferred to the grade of member at a
meeting of the Council held December
9, 1915:
BlERMAN, CHAS. F.
Telephone Engineer, Wisconsin
Telephone Co., 183 Fifth Ave., Mil-
waukee, Wis.
TRANSACTIONS I. K. S. — PART II
Bryant, Alice; G.
Physician, 502 Beacon St., Boston,
Mass.
Caldwell, F. C.
Professor of Electrical Engineering,
Ohio State University, Columbus, O.
Goldmark, C. J.
Consulting Engineer, 103 Park Ave.,
New York, N. Y.
Macbeth, Norman
241 W. 37th St., New York, N. Y.
Maxwell, James T.
General Agent, Philadelphia Elec-
tric Co., 1000 Chestnut St., Phila-
delphia, Pa.
McGuire, Frederick J.
Chief Inspector investigating illumi-
nating and power economies, Dept.
of Water Supply, Gas and Elec-
tricity, Municipal Bldg., New York,
N. Y.
Murray, Joseph Bradley
Acting Treasurer, Edison Electric
Illuminating Co. of Brooklyn, 360
Pearl St., Brooklyn, N. Y.
Rogers, S. C.
General Electric Co., West Lynn,
Mass.
Stafford, Raymond W.
New York Edison Co., 124 E. 15th
St., New York, N. Y.
Steinmetz, Charles P.
Consulting Engineer, General Elec-
tric Co., Schenectady, N. Y.
New Books.
Color and Its Application, by M.
Luckiesh, Physicist, Nela Research Lab-
oratory, National Lamp Works of Gen-
eral Electric Company, Cleveland, Ohio ;
360 pp., price $3.00; published by D. Van
Nostrand Company, 25 Park Place, New
York, N. Y. Contents: light; the pro-
duction of color ; color mixture ; color
terminology ; the analysis of color; color
and vision; the effect of environment
on color; theories of color vision; color
photometry ; color photography ; color in
lighting; color effects for the stage and
displays; color phenomena in painting;
color matching; the art of mobile color;
color media.
TF Illuminating engineering
700
133
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